Advances in Coiled Tubing Technology E&P Supplement 2006

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A custom publication to

1616 S.Voss, S.Voss,Ste. Ste.1000 1000 Houston,Texas 77057 Tel: (713) 993-9320 Fax: (713) 840-0923 840-0923

Editor in Chief BILL PIKE Director of Custom Publishing MONIQUE A. BARBEE Contributing Editor JOHN KENNEDY

Art Director ALEXA SANDERS Graphic Designer JAMES GRANT

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Production Manager JO LYNNE POOL

In addition to new tools, a better understanding and greater acceptance of the potential of coiled tubing have accelerated its recent growth.

For additional copies of this publication, contact Amy Carruth at (713) 260-6442. [email protected]

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Group Publisher, Newsletter Division DAVID GIVENS

Cutting Costs Cutting Costs,, Pro Providin viding g Access to New Reserves

There are two key elements of value in any drilling technique – cost-effective drilling performance and the ability to accurately place the wellbore to maximize production.

Corporate Director of Marketing JEFF MILLER

Group Publisher RUSSELL LAAS

Hart Energy Publishing,

Longer, Stronger Strings Longer, and Deploymen Deploymentt Tools

LP

Sr. Vice President and Chief Financial Officer KEVIN F. HIGGINS Executive Vice President FREDERICK L. POTTER President and Chief Executive Officer RICHARD A. EICHLER About the cover: The Tubing Intervention Manipulator is a new invention that enables coiled tubing (CT) rotation in both directions. It overcomes CT’s CT’s biggest limitation and promises a dramatic increase in capabilities capabil ities and applications applications.. This working working model, with three-quarte three-quarters-in. rs-in. CT on the spool, is currently rigged up on a well in Louisiana. Testing and development are under way way,, with participation by the inventor inventor,, John Van Way Way of Rental & Fishing Tools Inc., Lafayette Lafayette,, La., and the Mechanical Engineering Department at Texas A&M University.

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Versati ersatility lity and Box Box of Tools make make CT Ideal for Thru-tu Thru-tubing bing Work Work

Well maintenance and repair using a work string and tools that can be deployed through production tubing has long been the most common application of coiled tubing technology. With new fit-forpurpose tools as well as sophisticated software and telemetry, coiled tubing can perform an increasing variety of re-entry operations more effectively.

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Solutions take Shape for Subsea Intervention

If there is one market segment that poses the biggest challenge to coiled tubing technology, it is subsea intervention. Currently, it is a commercial challenge, too, although that eventually will change. Cover photo courtesy of Rental & Fishing Tools Inc.

EXPANDING COILED TUBING PROMISE

Longer, Stronger Strings and Deployment Tools In addition to new tools, a better understanding and greater acceptance of the potential of coiled tubing have accelerated its recent growth.

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s technology expanded capability during the past half dozen years, the number and types of coiled tubing (CT) operations have grown rapidly. Nearly 1,200 CT units were active around the world last year, up about 12% from 2004 and up from 850 units in 2001, according to the Intervention & Coiled Tubing Association (ICoTA). Canada and the United States each has about 250 units, together accounting for half the worldwide total, according to the association. In March, 292 CT units were active in the United States, an increase of 33 from a year earlier. By way of comparison, in late February, active rotary rigs in North America totaled about 2,250, according A coiled tubing operation is under way. (Photo courtesy of Schlumberger) to Baker Hughes. Coiled tubing service revenue jumped 27% last year to well cleanout technique that did not require the well to be shut $1.684 billion, according to Oilfield Market Report 2005 , prepared in. Now, it performs a lengthening list of workover and stimulaby Spears & Associates Inc. The report forecast an 18% increase tion operations. Drilling with CT promises to be one of its in revenues this year. fastest-growing applications. Much of the CT potential stems from a unique characteristic No longer a niche technology, CT is steadily closing the gap of the technology – it can have an important role in a variety of between its capability and that of traditional jointed pipe.Among operations throughout the life of a well or field. the operational benefits of CT are a relatively fast speed into and “You can use coiled tubing to drill, to deploy production out of the hole, as well as the ability to perform live well operatubulars, to service the well, even to [plug and abandon] the well tions. It can eliminate the need for a more costly workover rig. at the end of its life,” said Dennis Dunlap, president, CT business The ability of CT to be pushed through highly deviated holes unit for Precision Tube Technology. “Today, wherever in the and long horizontal sections is being extended by higherworld there are oil or gas operations, coiled tubing is there to strength coils and new deployment techniques.Temperature limsupport it.” its on tools are also being raised, and government and industry are involved in a sizable list of research and development efforts to further expand CT capability. CLOSING A GAP A continuous tubular manufactured in various lengths and Cost pressures, improved tools and equipment as well as spooled onto a reel, CT was first used mainly as an inexpensive industry’s efforts to shrink the surface footprint of operations are

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www.eandpnet.com • November 2006


fueling the g rowth of CT activity. As well intervention requirements continue to increase, CT can offer advantages for a range of well types, from shallow low-productivity wells in mature fields to subsea completions in deep water. Well service/workover applications still account for more than 75% of CT operations, according to ICoTA, but technical advancements have increased drilling and completion capability. Strong growth is expected in the use of CT for drilling, fracturing, subsea intervention, deeper wells and pipeline/flowline installation. Traditional applications will also continue to grow, including well unloading, cleanout, acidizing/stimulation, permanent velocity strings, fishing, tool conveyance, well logging, and setting and retrieving plugs. ICoTA cites these benefits of CT: • safe and efficient live well intervention; • rapid mobilization and rig-up; • ability to circulate while running in or pulling out of the hole; • reduced trip time, resulting in less production This downhole tractor system includes a turbine and wheels. (Image courtesy of Welltec Inc.) downtime; • reduced personnel requirements; and workover applications. Larger sizes are available for other • potential for significantly reduced cost. applications. Today’s injector heads can apply a greater force to A CT unit includes the reel for storage and transport of the CT; push or pull the string, and well control equipment can hanan injector head that provides the force to run and retrieve the CT; dle the 10,000-psi to 15,000-psi environments now becoming a control cabin; and a power unit to generate hydraulic and pneu- more frequent. matic power.Well control equipment is a critical element, since most During the past 5 years, manufacturers have also introduced CT operations are performed under wellhead pressure. higher-strength materials to meet the demands of deep well and Coiled tubing technology is a key part of a range of compati- high-pressure applications. Two decades ago, CT was used only ble and related wellbore intervention technologies that are growing on relatively simple wells where pressures above 5,000psi were steadily, including electric wireline tractors and slickline systems, rare. Now, 10,000psi is encountered routinely, and some jobs are said Gordon Mackenzie, product line manager for thru-tubing being performed in a 15,000-psi environment. intervention with Baker Oil Tools and ICoTA co-chairman. “Longer, bigger and stronger is the trend,” Dunlap said. Coiled tubing intervention is likely to use more than just CT. Early this year, there was a different materials challenge In CT drilling, for example, electric wireline installed inside the brought on by CT’s recent growth. Demand for CT was contubing is a compatible technology. Formerly the International siderably ahead of supply, creating a backlog that was nearing Coiled Tubing Association, ICoTA’s new name “reflects a natu- 6 months. ral diversification to involve these related intervention technolo“Getting pipe is difficult, so planning is critical,” said Perry gies,” Mackenzie said. Courville, manager for CT and hydraulic workover with Halliburton Energy Services. “Projects that require a special string are especially hard to get.” LONGER AND HEAVIER “Coiled tubing is being used in deeper wells and more difficult conWith demand for CT services strong, supply constrained, ditions, as the applications continue to expand,” Dunlap said. and growth of unconventional and new CT applications, CT That has driven an increase in the size and weight of a typical service providers are forced to get more life out of a CT string, string. Today’s average CT string is an estimated 5,000ft (1,525m) said Warren Zemlak, Schlumberger business development manlonger than the average a decade ago, and average weight has ager for CT services.That is driving Schlumberger’s interest in increased by 30,000 lb. new coil metallurgy, including compositions for sour service, Tube size has been getting larger, too. Precision Tube and a focus on advanced fatigue modeling and monitoring Technology, a wholly owned subsidiary of Maverick Tube technology. Monitoring damage – as well as fatigue – is also Corp., manufactures 2-in., 2 3/8-in. and 2 7/8-in. CT for well increasingly important.

Advances In Coiled Tubing Technology • www.eandpnet.com

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Advances in real-time pipe management and inspection will help extend CT life under increasingly severe conditions, Zemlak said.

“That combination extends the depth and pressure capability in an H2S environment,” he said. “It mitigates the losses that would otherwise occur.” A chrome material can provide a longer life for the coil because it does not rust like carbon steel. However, it is more senNEW MATERIALS MEET NEW DEMANDS “Today’s coiled tubi ng is far super ior to anythi ng we have run sitive to acid, Courville said,and in a service application,care must as recently as 5 years ago,” said Dan Bohannon, vice president be taken when pumping chemicals through a chrome alloy string. for CT and nitrogen services with Cudd Energy Services. Both 16-chrome and 19-chrome materials introduced for wells “Manufacturers have done a much better job with manufactur- with wet CO2 production are suited for permanent velocity strings ing and quality control.” in gas wells, for example, a significant application in North America. Coiled tubing is made in diameters ranging from three-quarters In Canada, 16-chrome is being used for CT fracturing in. to 5 in., typically from steels with yield strengths from 55,000psi because a smoother inner diameter allows higher flow rates at the to 120,000psi. Since the tubing is repeatedly plastically deformed in same pressure. It also appears that 16-chrome has greater resistnormal use, fatigue is an important design consideration.The tube is ance to abrasion when fracturing slurries are pumped. straightened as it comes off the reel, bent again as it moves into the However, 16-chrome has not been adopted as a standard CT guide arch, then straightened again as it is injected into the wellbore. intervention string for several reasons, including maintenance and The deformations are repeated as the string comes out of the hole. repair difficulties as well as incompatibility with certain fluids. Most CT strings are carbon steel. Recently, higher strength A number of different CT metallurgies have been proposed and steels have been used for coils to be used in deeper wells.Yield examined, including titanium and beryllium copper. It has always strengths of 110,000psi and 120,000psi are increasingly important been an economic balance, said Alex Crabtree, product line technolin applications that require greater depth and pressure capability, ogy manager for CT with BJ Services Co. Courville said. Because some of these products are new, they are Exotic metallurgy can extend the life of CT, but while titanium, “non-standard” and still pose some operational issues. for example, might multiply fatigue life by six to eight, it will cost six to eight times more than steel. Inspection and repair also become more difficult with exotic alloys. “YOU CAN USE COILED TUBING TO DRILL,TO DEPLOY Cost becomes a bigger factor as the base cost of material PRODUCTION TUBULARS, TO SERVICE THE WELL, rises and strings are larger and longer. EVEN TO [PLUG AND ABANDON] THE WELL AT THE “If it costs six times more to make the string out of an END OF ITS LIFE.” exotic alloy, that becomes a massive capital outlay,” Crabtree Dennis Dunlap, President, Coiled Tubing Business Unit, Precision Tube Technology said.“On balance, for both technical and commercial reasons, steel is pretty tough to beat.” The reliability of CT pipe has improved during the past 20 years. Now, corrosion and sour attack are more important FIGHTING CORROSION Steels for severe corrosive environments have also been developed. in CT management. Internal corrosion by brines, especially seaIntroduced in 2003, QT-16Cr was developed for direct exposure water, is the cause of a large share of corrosion incidents. to wet carbon dioxide (CO2) environments.Within a year, more “BJ has not seen a ‘pure’ fatigue failure – a failure caused only than 30 strings were in service for depths greater than 18,000ft by cycling the pipe – in almost 9 years,” he said. (5,490m), according to ICoTA, Early applications were as perThe No. 1 issue in CT operations is corrosion, Crabtree said. manent velocity string installations. In addition to corrosion resistance, the alloy has greater abra- COMPOSITES? MAYBE…SOMETIME sion resistance and better fatigue life than carbon steel. Tubing made of fibers embedded in a resin matrix – a composite – 2 Hydrogen sulfide (H S) service capability is an area of has been the focus of research and experiment. Changing the mix of increasing focus on the part of operators and service companies. fibers, orientation of windings and the resin properties can change The basic metallurgy of steel CT is relatively well known and its the performance characteristics of the composite material. fatigue life, as higher H2S conditions are encountered, fairly well First used for velocity strings in the late 1990s, operators and understood. Because CT is repeatedly plastically deformed, there service companies have been interested in composite CT for a is a need to further quantify the effect of H 2S on coiled tubing. decade, but CT made from composite materials has not yet For applications involving H2S, there is still some uncer- proved commercially viable and most of the work has been distainty about the acceptable upper limit on yield strength. An continued. Composite tube is still being made, but primarily for 80,000-psi yield is considered the nominal limit, but specialty pipeline applications, not downhole use. Halliburton has successfully run a 90,000-psi yield-strength The lighter weight of a composite string would be an advantage, steel with an inhibitor, Courville said. especially in deep wells, but higher temperatures pose a challenge.

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A key goal – cutting non-productive time attributed to equipment design by 75% – will be met, he said. Crew size requirements are also being addressed by incorporating ways to work smarter, as finding enough experienced people continues to be a challenge. With offshore operations in mind, all elements of the design are aimed at reducing lift weight and space requirement. The number of moving components, pumps and systems is minimized and electric systems have replaced hydraulic components in the control system and the control cab. Well control has also been reconfigured and a new reel design incorporated. “An advanced condition monitoring capability will allow the CT specialist to focus on the intervention operation, not solely on running the equipment,” Zemlak said.

The DeepWave tool on coiled tubing forces trapped liquids out, or treatment fluids in. (Graphic courtesy of Halliburton) Dunlap added that most CT strings are retired because of damage in the field, not because they have reached the end of their fatigue life. It is more difficult to repair damage to a composite tube than to a steel tube. Composite tubing also has a higher initial cost.The result is that the primary selling point of composite tube – a longer fatigue life – is not as significant an advantage, Dunlap said. Cudd has run composite CT, but Bohannon expects the market to take some time to develop, if it does.

DEPLOYMENT, OTHER OPERATING CHALLENGES As well completions become more complex and horizontal intervals get ever longer, deploying anything into these holes, including CT, requires increasing capability, downhole and at the surface. In its pursuit of “surface efficiency,” Schlumberger recently took a fresh look at CT systems using its in-house database of 60,000 jobs.The goal was to pinpoint recurring equipment problems and safety issues as well as analyze non-productive time. “We used that information to help design, develop and set specifications for the next generation of coiled tubing equipment,” Zemlak said. “We’re now launching the first seven offshore base units for field testing.”


HELPING PUSH AND PULL “Tractor technology helps extend the limits of what coiled tubing can do,” said Brian Schwanitz, vice president and general manager of Welltec Inc.Welltec is a Danish company founded by the inventor of the Well Tractor, Jorgen Hallundback, who began operations in the North Sea in 1996. “It’s an enabler that will make it possible to do things in extended reach wells that are not possible without the technology,” he said. Typical applications of the tractor in CT operations have been in treatments, cleanouts, extended reach drilling and helping to convey long strings of perforating guns. Tractors are increasingly being used for long horizontal intervals where pipe previously was relied on to convey services. As the lateral extent and the number of extended reach wells continue to grow, tractors will see more use, Schwanitz said. A 3 1/8-in. CT tractor powered by a turbine has been available since 2000. Drive fluid is pumped through the CT, turning the turbine, which generates power to run the self-contained hydraulic system that drives the tractor’s arms and wheels. Though use of Welltec’s tractors for CT operations is growing, it still represents only a small share of the company’s total tractor jobs; the rest are for electric wireline applications.With 16 bases in 23 countries,Welltec averaged about two CT tractor jobs per month early this year. Its wireline tractors have been in service for 10 years. “We need to get the word out that coiled tubing tractors are a good option for the growing number of extended reach applications,” Schwanitz said. For drilling, the Welltec tractor goes in the hole completely flush.When the pump rate reaches a preset level, say 2 bbl/min, the tractor is activated and deploys its arms and wheels. If the pump rate drops back below that level, the tool will deactivate and close up flush again.The closed hydraulic system powers an individual hydraulic motor on each wheel. The hydraulic system is a constant-capacity system. Varying the number of operating wheels can change its operation. For maximum force, for example, all the tractor wheels – up to 20 in one tractor – can be operating; for maximum speed, only eight wheels might be operated.

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BJ SERVICES

Paid Sponsorship

BJ Advances Coiled Tubing Methods and Technologies BJ Services coiled tubing (CT) experts develop new CT equipment and techniques to solve specific problems for oil and gas operators. Along the way, they often create new technologies that go beyond mere enhancements to conventional tools.

B

J’s CT tradition stresses continuous improvement. The company creates new tools and systems to improve traditional CT applications, enhance safety in all CT uses and make CT an enabling technology for addressing well problems that once went unsolved or enable applications in wells that would otherwise be impracticable.

• nitrogen jetting or fluid lifting; and • perforating. The backbone of CT applications is well cleaning: removing sand, scale deposits and other debris from producing oil and gas wells. Early technology often accomplished the job, but BJ professionals have improved treatment efficiency by designing and building advanced tools such as downhole phase separators and specialized jetting nozzles. NEW LIFE FOR CT CLASSICS BJ provides state-of-the-art tools for all Within BJ, well cleanouts have evolved the classic CT application areas: into very specialized systems and techniques • well cleanouts; that greatly improve efficiency for specific • spotting/squeezing fluids; well cleaning tasks. Compared with CT • stimulation; tools that merely spray fluids, for example,

BJ rotary jetting technologies use less fluid and cover the wellbore more efficiently: • The Roto-Jet ® tool and nozzles provide the most effective high-energy pressure jetting for tough wellbore problems like bar ium sulfate scale. • The patented Roto-PulseSM method offers controlled-energy fluid placement for cleaning plugged gravel packs without appreciably altering pre-packed media. • The BJ Vortex nozzle simply and economically places treatment fluids via CT. In the Niger delta, BJ has used this nozzle to clean and acidize wells in a single trip.

BJ crews routinely provide coiled tubing drilling services throughout western Canada.

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BJ SERVICES

• BJ’s patented TornadoSM cleanout process efficiently sweeps virtually all obstructing solids from the wellbore, even from extended-reach horizontal wells. In a recent Arabian Gulf application, the BJ Tornado process removed 15 bbl of fill from about 400ft (120m) of perforations in one pass. The Tornado tool’s forward- and reverse-jetting nozzles reduced cleaning costs and job time by nearly 70% compared with a conventional CT cleanout.

TAKING CT PERFORMANCE TO NEW LEVELS New field problems challenge BJ to perform under economic and operational conditions other technologies have been unable to solve. The BJ DuraLink TM CT connector provides an effective mechanical means for quickly coupling two CT strings offshore. This BJ self-erecting mast unit in south Texas epitomizes rig-up efficiency. Where platform crane lift capacities limit the size of CT reels, the DuraLink conIn a complex variation on CT fractur- enabled natural flow – a first among that nector offers an economical and reliable ing, an operator in Norway asked BJ to field’s wells. Additional wells have seen solution for entering deep or extended- provide CT acid fracturing for a new similarly successful treatments. reach offshore wells. offshore well. Ineffective fluid diversion For multi-zone reservoirs, BJ’s during bullheading treatments bypassed EVOLUTIONARY CHANGE, OptiFracSM service saves operators time important perforated zones. BJ-developed REVOLUTIONARY RESULTS and money on fracture stimulation, with CT tools selectively and accurately stimu- BJ’s proprietary CIRCATM modeling and without proppant or nitrogen gas assist. lated 15 zones in one trip using between software evolves with each new tool or 50% and 80% less acid. The well produced technique. Roughly 20 years of increenough oil for operational payback after mental improvements make the CIRCA just 11 days. Production stabilized about program one of the most robust tools in 11,200 b/d of oil, more than twice what BJ’s kit. BJ personnel routinely use the operator expected from bullheading. CIRCA analysis to precisely plan and Back on land, BJ developed CT tools execute CT operations. and technologies for the Pohokura gas field In the hands of BJ experts, CT techin New Zealand. Operational challenges nology routinely improves production culminated in accurate CT perforating and extends the useful life of wells under runs under pressure in three onshore wells virtually any conditions. As operators reaching (nearly horizontally) as far as push the envelope, BJ makes sure its CT 24,400ft (7400m) offshore. capabilities keep the pace. Most recently, a Latin American operator gained significant production increases with BJ’s new StimTunnelSM technology, which uses CT acid jetting to create multiple productive laterals in carbonate formations. The technique uses far less acid to provide greater reserBJ Services Company 11211 W est FM 2920 • Tomball, TX 77375 voir access than acid fracturing or matrix Tel: (832) 559-1303 • Fax: (832) 559-1319 BJ rotary jetting technologies use less fluid and acidizing. Its initial field application www.bjservices.com cover the wellbore more efficiently. tripled the well’s original production and


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The Emergency Stop System helps avoid failure. (Image courtesy of CTES) Maximum force from one tractor is about 3,500 lb, but two tractors in tandem with a total of 40 wheels has provided 7,200 lb of force, Schwanitz said. A tandem arrangement can also help negotiate sections with extensive washout. Each wheel has an “anti-spin” valve to prevent it from robbing power from the other wheels by spinning freely, for example in a washed out section of the hole. “It’s much like a car’s posi-traction system,” Schwanitz said. The tractor can negotiate restrictions without losing traction. The individually suspended wheels will follow the internal inner diameter (ID) and maintain the drive through the restriction. If communication with the tractor is lost, it will collapse back into the same outer diameter (OD) as when entering the well. Coiled tubing can also provide flow assurance in pipelines plugged by paraffin or hydrates, sand or scale, Schwanitz said.The tractor can provide the force needed, for example, to push a mill bit through to eliminate a blockage.

OTHER OPTIONS Another tool in use to extend reach is an “agitator.” Andergauge’s AG-itator,for example,provides axial excitement by converting pressure pulses within the tool.The pulses vibrate the string to break the static friction that inhibits movement.According to Andergauge, initial testing on 2-in. coiled tubing reduced friction by 95% and prevented the onset of helical lock up.

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An externally tapered OD string is another approach to increasing deployment capability. A tapered string can extend the depth to which CT could be used. The ID remains the same throughout a tapered string, preserving flow capacity, but a smaller OD on the bottom of the string reduces weight. The ability of a conventional CT string to perform ultra-deep work depends primarily on its total hanging weight and the yield strength of the parent metal. If the hanging weight exceeds the pipe’s yield strength, the string can separate.A tapered string provides greater strength at the upper end of string, but a lighter coil. During the past 5 years, the number of wells drilled to depths below 25,000ft (7,625m) has increased dramatically, according to Halliburton. Its DeepReach service can extend the current depth of high-pressure CT operations in deepwater deep wells to 32,000ft (9,760m) total vertical depth and is compatible with 15,000psi wellhead pressure control equipment. DeepReach,using multiple sections of CT with different ODs in a single string, can extend reach in deep and ultra-deep wells by 30% compared with conventional CT strings.The service is designed to help recover hard-to-access reserves in deep water and perform treatments on ultra-deep wells that were virtually impossible previously, according to Halliburton. Development of the service was a joint project between BP and Halliburton. Quality Tubing, Texas Oil Tools and CTES also were involved in the development team.



Field trials for the system were conducted in South Texas in late OPERATING SAFELY 2004 using a 13,000-ft (3,965-m) string with a 2-in. OD upper sec- As CT activity grew rapidly last year and early this year, a chaltion and a 1 3/4-in. OD lower section. Later tests used a 2-in. OD by lenge for CT service companies – as it seemed to be for all 2 3/8-in. OD string. industry segments – was finding enough skilled CT unit operaSeveral key technologies were developed to make the design tors to operate new units being deployed in the field. work for deep wells, according to Halliburton: transition joints;VLimited experience always makes safety more important. shaped gripper blocks used in the injector head; modifications to With multiple events requiring their immediate attention in the the injector head; and variable diameter well control equipment. control cabin during a field operation, even highly seasoned Aside from deepwater and deep wells, externally tapered OD operators may be momentarily distracted, said Ed Smalley, senior strings can be an option for weight-sensitive offshore platforms. vice president of CTES LP. Weight can be especially critical on older platforms where cranes CTES developed its Emergency Stop System (ESS) to help may have been de-rated. avoid sudden operational failures that can result from these temThere is another deployment option available to cope with porary distractions. A user-definable injector stop system, it is larger reel weights and sizes. Coils can be taken to location in designed to avoid catastrophic buckling or parting of the CT two sections and joined together on location by welding or with string and can be retrofitted to any CT unit. a mechanical connector. “Experience is important in avoiding these problems, of Welding CT is not simple and a welded joint reduces the course,” Smalley said.“But the attention of even the best operanumber of allowable string cycles. Welding equipment, inspec- tor can also be diverted at the worst possible moment.” tion equipment and skilled people must all be taken to the well If that happens while going in the hole near a restriction or site if welding is to be done. while nearing the bottom of the hole and tubing continues to be To eliminate the need for welding on location, BJ Services inserted, it can buckle at the surface below the injector. When has developed a mechanical connector, Spoolable DuraLink, for coming out of the hole, if the tubing becomes stuck, it can part joining two coil lengths mechanically on location. At the well if too much pull is exerted. site, the two lengths are joined and the entire length spooled on to one working reel.After the job, it is separated “COILED TUBING TECHNOLOGY IS A KEY PART OF A into two lengths for the return trip. The option is most applicable for offshore work where BROAD RANGE OF COMPATIBLE AND RELATED WELLdividing a 40-ton reel into two 20-ton lifts that can be lifted BORE INTERVENTION TECHNOLOGIES THAT ARE onto most platforms makes it possible to operate the GROWING STEADILY…” Gordon Mackenzie, Product Line Manager,Thr u-tubing Intervention, Baker Oil Tools; working reel on the platform. Spooling from the boat Intervention & Coiled Tubing Association Co-chairman onto the platform is also an option, but that operation is weather-dependent. The ESS continuously monitors four parameters to provide REAL-TIME CONTROL proper injector control. Minimum weight can be used to stop At its heart, CT technology application is all about cutting the injector when going in the hole and the bottom end of the costs. To do that requires a constant knowledge of operating coil encounters an obstruction. Maximum weight settings can be conditions and the ability to adapt the operation to the latest used to activate the system when coming out of the hole and the information. string becomes stuck downhole. Electric line is a proven technology for communicating The operator can continuously adjust the maximum and between the surface and the bottom of the hole, but reliability minimum weight settings as more tubing weight is run into or and cost often restrict its use in routine applications. To expand out of the hole. However, if the operator fails to update the telemetry capability for intervention operations, Schlumberger settings during the operation, failure could still occur unless has applied the knowledge gained in developing fiber optic tech- another parameter is monitored. nology for its completion services. To mitigate this risk, the ESS also monitors the rate of weight “We put a lot of effort into modeling and design based on reser- change. voir and other parameters,”Zemlak said.“The goal is to use real-time “Even if the operator fails to update the weight settings during information to optimize the job as it is executed.And over the long the job, the system is ‘idling’ in the background to provide protecterm, it is important to take some basic downhole measurements in tion. If it sees a significant change in the rate of weight change, the every operation to help optimize results.” system will activate, the injector will stop, and the brake will be Schlumberger’s fiber-optic-based iCoil platform will include a set,” Smalley said.“Then the operator can review the situation and number of services, the first of which will be commercialized “in the decide how to proceed.” very near future,” Zemlak said. Along with the rate of weight change, the system monitors CT

Advances In Coiled Tubing Technology • www.hartenergy.com

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speed to help avoid unnecessary shutdowns. If the speed is very slow, for example,it might indicate the coil is being picked up off the bottom or the operator is carefully watching weight. So the system would not inadvertently shutdown the injector under the slow speed condition just because weight has increased. “Because of the rapid expansion of coiled tubing work, and for economic reasons, we are getting a lot of interest in this system,” Smalley said.“It makes sense to add this feature to a standard coiled tubing data acquisition package.” Cudd uses a CT monitoring system and a conservative 80% of the pipe’s fatigue rating as a baseline.The result has been a significant reduction in the number of failures.The fatigue monitoring system provides better data on the presence and location of worn spots. Because it indicates when the string is close to the limit, it serves as a warning that a coil might not be suited for an application that involves high pressure or other severe service. “We use the more conservative baseline because the applications we are asked to look at typically involve higher pressure or other more difficult conditions,” Bohannon said.

HIGH TEMPERATURE/HIGH PRESSURE (HP/HT) “We’re seeing more and more HP/HT work,” Bohannon said. “It’s not unusual for us to work in 12,000psi surface pressure, and pressures above 7,500psi are common.” At high pressures, it can be difficult to pump enough fluid to maintain annular velocity in larger casing sizes. “Today, we are entering wells that have a surface wellhead pressure of 8,000psi to 9,000psi, so internal pressure in the coiled tubing is in the same range,” Crabtree said.“That would have been unheard of a decade ago.”

Fracturing is a key growth area for coiled tubing. (Photo courtesy of BJ Services)

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The number of wells BJ Services is working in at pressures approaching 10,000psi or higher is increasing as well. Coiled tubing blowout preventer systems rated for 10,000psi are not uncommon, and 15,000psi stacks are available. The continuing increase in temperatures faced by most tools, especially telemetry and electronic equipment, is a challenge for CT, which must be cooled when extracted from the well before it is wound on the reel. If it is coiled onto the drum without cooling, the tubing will contract and could collapse the drum or break. BJ has worked in wells with bottomhole temperatures to 450°F (232°C). Coiled tubing drilling operations have encountered temperatures between 256°F and 301°F (125°C and 150°C). Cooling can be done by circulating through the CT or with a cooling loop in the riser. A cooling loop has had to be included, for example, when working in geothermal wells. Baker Hughes’ acquisition of the independent U.K. company Zeroth Technology Ltd. (Zertech) has added an important capability to the Baker Oil Tools CT toolbox, Mackenzie said. “Zertech’s metal-to-metal Z-Seal technology provides a significant advantage for sealing systems on well intervention products like bridge plugs and straddles in an HP/HT environment,” he said. Coiled tubing is one of the main deployment methods for the Zertech product line. Z-Seal (patent pending) is a high-integrity, low-profile, higexpansion seal that may be entirely non-elastomeric. The sealing concept relies on the controlled application of load to expand the seal to achieve a fully formed pressure barrier, may be fully retractable and does not rely on memory.The controlled mechanism can allow for expansion ratios of up to 160%. By eliminating elastomeric materials from the wellbore seal and internal seals, operating temperature limits can be raised to 700ºF (371ºC) and pressure differential, depending on expansion characteristics, to more than 10,000psi. A metal-to-metal seal also eliminates much of the risk associated with chemical incompatibility, a significant advantage as more HP/HT developments around the world use expensive brines, including cesium formates. Schlumberger’s CoilFLATE service is designed to provide reliable zonal isolation in harsh environments.The HP/HT thru-tubing inflatable anchoring packer, designed for extreme conditions, eliminates the need for a workover rig because the packer is run on CT or jointed pipe into vertical, deviated or horizontal wellbores. Remedial operations can be performed without killing the well. The service also features an advanced multi-set straddle and an effective multi-set packer. CoilFLATE is available in multiple sizes for work in up to 9 5/8-in. casing.


Paid Sponsorship

CUDD ENERGY SERVICES

Technology, High-pressure Intervention Come Together Improving the performance of each well safely and efficiently is our business.

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n today’s market, coiled tubing (CT) technology is critical to the success of profitable oilfield operations. Cudd Energy Services’ field professionals provide a range of engineered well intervention services with CT, from a simple sand wash to an intricate high-pressure well recovery operation. Cudd aggressively pioneers new advancements in the use of CT, equipment design and technology for its customers in onshore and offshore environments. Cudd Energy Services’ technical support team and engineering staff use the most advanced software to calculate the optimum CT methods and techniques to maximize and enhance string performance. The integrity of the CT work string is carefully monitored during its operative life using the Orion® data acquisition system and Cerberus® real-time modeling and fatigue monitoring software.These systems are used in conjunction with a new transflective nearfield imaging touch screen display that increases brightness on the screen making it easier for the operator to quickly see critical data. Cudd also has an in-house comprehensive CT string database and proprietary string specification program to ensure each CT application is conducted within the specific string’s operational limits.

stress modeling to predict the best fit. Triaxial stresses are based on the widely accepted Von Mises Distortion Energy Theory for ductile materials. The theory uses a combination of the principal stresses of axial, hoop and radial in comparison with the material’s yield stress to predict the onset of failure. Although the CT manufacturing industry is held to high standards, Cudd Energy Services required verification of the actual geometric properties of the actual tubing to be used for this critical situation. Even after the tubing properties and geometries were verified, Cudd’s Corpus Christi, Texas, district and technical services group performed an additional test on samples of the CT. The Cudd pioneers new advancements in coiled tubing test objective was to simulate the conditions technology and equipment design. that would exist during the job.By performing the test in a controlled environment, the 3 1 /4 in. QT-900 CT, a thru-tubing solutions operations personnel had empirical proof to motor head assembly, Bronco Services support the stress model, show the equipwellhead equipment and a Stimulation ment was mechanically sound and ensure Services high-pressure pump along with the operation could be safely performed. other necessary surface equipment to Using proper material selection, sound maintain well control. engineering practices and verification testThe situation required careful pre-job ing, a solution was found and the operation planning to provide the best solution by successfully completed. The remediation minimizing exposure and providing a high was a success, and the objective for the cusprobability for success.Typically, CT oper- tomer was met. This example of using a ations do not involve such an extreme unique application combined with pre-job pressure-while-drilling or milling near the evaluation, communication, cooperation, HIGH-PRESSURE INTERVENTION Recently, Cudd Energy Services’ experi- surface, which made the situation unique. bundled services and field-testing create enced personnel and bundled services Hydrogen sulfide gas was also present, adding value for the customer. concept developed a way to utilize CT in to the complexity. This gas along with the a critical service application under extreme high pressures placed the CT and downhole pressures. A well bridged off at a shallow equipment in the corrosion stress-cracking 143ft (44m) with potential wellhead pres- region limiting the type of CT that could be sure in excess of 10,900psi. The bridge safely placed in the well during the intervenneeded to be removed prior to completing tion. If the stresses exceeded the yield stress Cudd Energy Services the next phase of well completion. of the CT, then failure could occur. 15015 Vickery Drive • Houston, TX 77032 The remediation plan called for a 15,000After initial material selection, Cudd’s (832) 295-4629 • www.cudd.com psi high-pressure CT unit, a short string of technical services group performed tri-axial


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CUTTING COSTS

Cutting Costs, Providing Access to New Reserves There are two key elements of value in any drilling technique – cost-effective drilling performance and the ability to accurately place the wellbore to maximize production.

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ith a g rowing choice of more reliable and capable tools, today’s coiled tubing (CT) drilling technology is increasingly competitive with jointed-pipe drilling in both these areas. There is another situation driving the growth in the use of CT for drilling. “Rig availability,” said Perry Courville, manager for CT and hydraulic workover with Halliburton Energy Services. “There is more interest now because it is sometimes hard to get a conventional rig.” A high utilization rate also has pushed conventional rig rates higher, adding to the interest in CT for a variety of drilling operations. “A number of jointed-pipe rig operators have migrated to the coiled tubing market,” Courville said, but CT drilling contractors have not moved into the traditional r ig market.

This diamond speed mill is on a whipstock ramp. (Image courtesy of Baker Oil Tools)

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Historically, there has been the perception that CT drilling was cheaper than traditional drilling. However, by the time all the requited tools are added to the end of the coil – a motor, special bits, other tools – the rate could approach that of traditional rigs. The most consistent CT drilling activity still is in Canada and Alaska. In Canada, under-balanced drilling with CT is common. Pressure controlled drilling – drilling at close to overbalance – and thru-tubing dr illing are being done in Alaska. Elsewhere, CT drilling has been sporadic, though some wells have been drilled in Europe, the Far East and the Middle East. Weatherford International Ltd. is running a new system in its CT drilling project in Algeria where formations are hard and abrasive. “It’s a tough area, but we’ve learned a lot and the project is going well,” said Michael Stulberg, global product line manager for thru-tubing. Coiled tubing was the choice for the multiwell project for a major operator in Algeria, in part because it is well suited to drilling in an under-balanced pressure condition. Rig availability and cost were also considerations. Weatherford is also active in CT drilling in Alaska and Canada, where short laterals are drilled for coalbed methane development.

FULFILLING ITS POTENTIAL There has been a dramatic increase in CT drilling dur ing the past 3 years, said Jimmy Gray, Baker Hughes Inteq product line manager for slimhole re-entry systems.“There have been significant advances in the reliability and the value of CT drilling and completion programs.” Coiled tubing is not yet a mature drilling technology, but neither is it in its infancy. Though no longer a niche, high-cost option, it needs to gain momentum, and cross over into applications where it has not previously been considered, to fulfill its full potential. Increasingly, CT drilling is being used in


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remote locations where “spread” costs are high and logistics are a challenge. Significant growth also is occurring in the mature fields of North America, where there has been a growing acceptance of the technology, Gray said. Coiled Tubing is also used to “finish” wells where a conventional rig is used to drill to the top of the pay and run casing. Then CT is used to drill the pay zone in an underbalanced condition. There also is renewed interest in using CT for exploration. “Many of the promises that coiled tubing offered in the past are now being fulfilled,” Gray said. Industry is more familiar with the technology and increasingly willing to consider it for more applications. “Fundamentally, CTD is reservoir driven,” said Alex Crabtree, product line technology manager for CT with BJ Services Co. “There are two key criteria in selecting candidates for coiled tubing drilling (CTD): can the well be drilled underbalanced – is the borehole stable, in other words – and will it be a better well if drilled underbalanced?”

• smaller footprint and weight; • faster rig up and rig down; • reduced environmental impact; • fewer personnel; and • availability of high-speed telemetry. Much of the CTD done to date has been in non-directional shallow gas development and shallow injection wells, and in holes smaller than 7 in., according to the ICoTA. Holes up to 13 3/4 in. have been drilled successfully, according to the association. Directional wells can now be drilled with CT, including new wells, extensions, sidetracks from existing completions and horizontal drain holes. Drilling with CT can also be done in an underbalanced or overbalanced pressure condition. In an overbalanced condition, the operation is similar to drilling with drillpipe. However, the CTD fluid system is typically smaller than that of a conventional rig and the smaller tubing diameter can limit flow rates.

OPENING THE CTD APPLICATION WINDOW Safety is a key advantage of CTD, especially in underbalanced SIMILAR BUT DIFFERENT From a manufacturing standpoint, the main difference operations. Eliminating jointed pipe reduces well control and between tube for drilling and tube for workover is diameter pressure management risk, and personnel are not required on and wall thi ckness. Precision Tube Technology has f ocused on a rig floor to make connections. Baker Hughes, for example, the ability to manufacture heavier wall tube and larger, heav- recently completed a 3-year project with no reportable lost ier reels of pipe during the past couple of years. A typical time accidents. drilling string of CT is now in the mid-range of Precision’s Advances in technology fueling the growth of CTD will manufacturing capability, said Dennis Dunlap, president, CT open the window of applications even farther, Gray said. business unit for Precision Tube Technology. Closed loop, automated systems will extend the lateral length capability of CT drilling. This “game changer” will bring more opportunities for CTD, he said, includ“THERE IS MORE INTEREST NOW (IN COILED TUBING ing mature basins, where underbalanced drilling operaDRILLING) BECAUSE IT IS SOMETIMES HARD TO GET A tions may be needed. Bypassed production and comCONVENTIONAL RIG.” partmentalized reservoirs are growing targets of proPerry Courville, duction enhancement efforts, and CTD offers advanManager, Coiled Tubing and Hydraulic Workover, tages in accessing these zones. Halliburton Energy Services Especially in North America where large fields are not being discovered, a return to mature basins to Coiled tubing drilling can be used to drill many of the develop new zones or stem decline curves is increasingly same types of wells as conventional rotary drilling, and ele- attractive. ments of CTD systems are similar to those of rotary systems A closed-loop drilling system enables that search as do using jointed drillpipe. advances in high-performance downhole motor technology. For vertical wells, CT uses a drilling assembly with a For example, Baker Hughes’ X-treme motor line features a downhole motor similar to the bottomhole assembly (BHA) contoured stator technology that can increase at-the-bit for conventional drilling. For directional drilling, CT is horsepower dramatically, compared with conventional posisteered much the same as conventional rotary drilling. tive displacement motors. Parameters are also similar for bit design and selection, Historically, whether in a 2 3/8-in. or 3-in. BHA, power whether for CT or conventional drillpipe. that could be delivered to the bit was limited. New motor The benefits of CTD tend to reduce cost compared with designs have made a step-change increase in this capability, conventional rotary drilling, according to the Intervention & Gray said. Coiled Tubing Association (ICoTA), including: “Projects that might not have been drilled with coiled tub• safe and efficient pressure control; ing in the past are now candidates for the technology,” he said. • faster tripping time (150+ ft/min); To cope with deeper wells, Baker Hughes has focused on


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reducing overall wellbore tortuosity through the use of automated systems. “Using what we’ve learned from rotary steerable systems and vertical dr illing systems like VertiTrak, we have been able to package that in a smaller configuration for CT drilling,” Gray said. During the next 3 to 5 years, there will be additional applications including multilateral completions and the ability to place liners to improve wellbore stability, he said. In multilateral completions, eliminating pipe connections mitigates hole-cleaning and hydraulics issues that would arise in drilling through depleted or nearly depleted reservoirs. Differential sticking that can occur in an overbalanced situation can also be minimized when downhole pressure is accurately controlled. Baker Hughes’ CoilTrak system includes a drilling performance sub that provides real-time weight-on-bit, downhole torque and vibration analysis so operating parameters can be modified in real time to drill a smoother wellbore. “The system is fully interactive,” Gray said. “We can now ‘joy-stick drill’ routinely, something that was considered science fiction a few years ago.” Combined with formation evaluation sensors, it is possible to navigate more precisely in the reservoir. Full resistivity and gamma measurements in real time – not in a memory or logging mode – make it possible to steer into production. This technology has removed a significant disadvantage of CTD compared with conventional drilling. Formation evaluation and sensor packages were previously not available in the tool size needed for CTD. “It is a big step change, and it will continue to open the window of applications, especially in areas of geological Three and three-quarter-in. PDC bit is optimized for coiled tubing operations. (Image courtesy of Hughes Christensen) uncertainty,” Gray said.

THE BUSINESS END An expanding choice of fit-for-purpose bits is also available for CTD and other CT operations. Hughes Christensen is designing optimized polycrystalline diamond compact bits specifically for CT applications. In Alaska, where CTD continues to gain momentum, a 3 3/4-in. Hughes Christensen STX404 drilled the Ivishak Z1A sand/shale build and lateral sections with one bit.The initial objective was to construct the build section then verify the bit’s condition. The four-bladed PDC bit was pulled in good condition and tripped back in the hole to finish the well. Job details include: • Build section —419ft (128m) in 10 hours, average deviation of 20.13º/100ft (31m); • Lateral section —1,867ft (570m) in 27 hours, an average of 69.15 ft/hour (21m); • Total —2,286ft (697m) in 34 hours, for an average of 61.78 ft/hour (19m).

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WATCHING FATIGUE, AVOIDING LOCKUP Because it is repeatedly plastically deformed, coil fatigue is a concern in any CT operation. Drilling with CT typically increases fatigue compared with other CT operations. Under “normal” CT use, a string might last between 30 and 100 jobs, said Ed Smalley, senior vice president of CTES LP. When used for drilling, depending on the operation, the maximum number of jobs might be less than half that. To keep a closer watch on fatigue, the monitoring software package CTES developed for standard CT operations also works well for drilling, he said. “When fewer jobs can be done with the string, it becomes important, especially when drilling extended reach laterals, to monitor fatigue in real time,” Smalley said. The CTES system monitors the percentage of fatigue life used; most coils are retired after about 80% of the fatigue life has been used. The calculation is specific for each CT size, wall thickness and yield strength and includes the field-operating environment – gooseneck and CT reel size, internal pressure – to provide accurate results.


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drilling have been in Alaska,” said Gordon Mackenzie, product line manager for thru-tubing intervention with Baker Oil Tools and Intervention & Coiled Tubing Association co-chairman. Typically, a CT casing exit is done in two trips; on the first electric wireline trip, the whipstock is set and positioned, on the second trip, the window is milled. Most windows are milled with a diamond speed mill. Introduction of Baker Hughes’ Navi-Drill X-treme workover motor has helped expand casing exit capability. Its shorter-than-average length and greater-than-average torque capabilities are important features when working with CT. Another recent advance has been the ability to cut exit windows in exotic materials. Since Baker Oil Tools performed the Two coiled tubing units perform simultaneous jobs on two wells. (Photo courtesy of Halliburton) first 25%-chrome exit in the U.K. North Sea in 2002, interThe software can also predict whether a tractor will be est in making exits through high chrome materials and nickneeded to pull a string through an extended reach interval, el alloys has grown steadily. and how much force the tractor needs to provide.The tractor “That’s where thru-tubing casing exit research and design is used to help avoid CT “lockup,” which occurs when the are headed,” Mackenzie said. coil continues to be pushed from the surface but it has heliResearch and development (R&D) is also focused on cally buckled at the section of highest compression because of extremely underbalanced environments. the wall contact friction force. At the point of lockup, less When a major operator drilled a series of laterals in a gas than 1% of the force applied at the surface is transferred to the field in Sharjah, for example, gas production was not shut bottom end of tubing and forward movement stops. down during milling of the exit window and the subsequent “Lockup can be a significant challenge when using coiled drilling of the openhole zones. tubing to drill long horizontal wellbore sections,” Smalley said.

“THERE HAVE BEEN SIGNIFICANT ADVANCES IN THE GETTING A LATERAL STARTED RELIABILITY AND THE VALUE OF COILED TUBING Coiled tubing is increasingly used as a technique for DRILLING AND COMPLETION PROGRAMS.” drilling laterals out of existing wellbores.The first step in Jimmy Gray, that process is to mill a window in casing so drilling can Product Line Manager, Slimhole Re-entry Systems, Baker Hughes Inteq begin. Coiled tubing sidetracking did not begin to gain real acceptance until the mid-1990s. Since then, Baker Oil Tools has gained extensive experience in using CT for casing For such applications, Baker Oil Tools has developed systems exits. Since 1996, the company has performed more than 350 for almost-pure nitrogen operations. Cooling and controlling casing exit jobs globally and has developed casing exit tech- vibration present challenges in a nitrogen environment. On the niques and tools for monobore and thru-tubing environments. Sharjah job, a small amount of injected liquid was permitted to “The proving ground and early adopters of coiled tubing help cool the bearing section in the workover motor.

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CUTTING COSTS

about 18,200ft (5,551m). Then a low-side openhole sidetrack CBM AND SHALLOW FIELDS Coalbed methane (CBM) and shallow well drilling are prime was drilled at 17,950ft (5,475m) measured depth, and direcapplications of CTD.Wells are typically not complex and the tionally drilling continued to about 18,350ft (5,597m). A logistics of getting pipe to the location is seldom a challenge. 2,600-ft (793-m), 2 3/8-in. slotted liner was set in the open hole. In these applications, a large number of wells are usually conIn long horizontal or high-angle holes, tractors can dratained in a limited geographical area, another characteristic matically extend the reach of CT operations. A downhole that plays to the strengths of CTD. tractor can push the string to the target depth and apply the Much shallow drilling is done with CT rigs in Canada, for downhole force needed to operate tools. example, in areas with dense well populations. Coiled tubing Without a tractor, the reach of CT varies with several drilling is often not an economical option for a few wells, but parameters, including the size of the coil and hole. Smalldrilling between 300 and 400 wells with several rigs can diameter CT in a large hole will not go far in a horizontal or bring significant cost savings. high-angle well, perhaps 1,000ft (305m). Larger CT – 2 in. Coiled tubing occupies a smaller footprint, too, often a or more – inside a smaller hole can be pushed farther. consideration in the areas where CBM and more mature “The practical limit without using a tractor, even with a fields seem to be located, especially in North America. Any larger tubing in a small hole, seems to be somewhere smaller hole makes fewer cuttings, and requires less fluid and between 3,500ft and 4,000ft [1,068m and 1,220m],” said equipment. Brian Schwanitz, vice president and general manager of Canada is expected to stay active as shallow gas fields and Welltec Inc. CBM fields are developed in Alberta. Some Canadian operaThat limit applies, in general, to holes deviated more than tors are entering the U.S. Rocky Mountain region, too, 70º, where gravity is providing little or no help. where CBM is also being developed and more CTD is expected. The wells are deeper than those in Alberta, however, so coils used in Canada often do not hold “FUNDAMENTALLY, COILED TUBING DRILLING IS enough pipe for the Rocky Mountain drilling. RESERVOIR DRIVEN.” “We’re doing some technologically extreme CT Alex Crabtree, operations. But at the same time, we are focused on Product Line Technology Manager, Coiled Tubing, BJ Ser vices Co . brownfield applications,” said Warren Zemlak, Schlumberger business development manager for CT services. As more fields decline, CT is uniquely suited to completIn addition to extending the reach of CTD, the tractor proing wells and maintaining production. In the past, CTD and vides a constant weight-on-bit while drilling, helping to avoid multi-zone fracturing, for example, were niche applications; the “stick/slip” problem, which can wreak havoc with drilling today those are “mainstream.” efficiency. In a stick/slip situation, bit weight can change draCoalbed methane and alter native gas development will see matically as the string shifts from the stick condition to the slip increasing use of unique CT technologies such as multilateral condition, possibly stalling the bit and motor. Drilling with a completions, to improve reservoir drainage and reduce the tractor also controls reactive torque, Schwanitz said. surface impact of drilling operations. Welltec has been able to pump as much as 3 bbl/min of “Re-entry into existing wellbores will be a real opportu- drilling fluid through its tractor with a mud motor on the nity for CT drilling,” Zemlak said. end of the tractor and the bit at the bottom. Surface readout of weight-on-bit has shown the tractor was providing up to 2,300 lb of additional weight-on-bit during drilling. EXTENDING EXTENDED REACH Horizontal drilling continues to set new records for reach. Welltec has performed five CT drilling jobs in Prudhoe There is growing interest in “ultra extended reach” holes that Bay where the goal was to prove the concept of getting extra could extend 12 1/2 miles to 18 3/4 miles (20 km to 30 km) reach, Schwanitz said. Many of the targets are right at the from the surface drilling location. limit of what CT can do without the help of a tractor. Coiled tubing drilling is setting records in this arena, too. “So far, we have been able to reach bottom in most of the Schlumberger set three new records when it successfully wells we’ve worked in by tailoring the tubing string to the completed a directionally drilled well in Alaska using its well,” Crabtree said. Dynamically Overbalanced Coiled Tubing Drilling techBut as horizontal intervals get longer, tractor systems will nique with an electric line inside 2-in. CT. be more important.Tractors typically cannot pull the tubing A window was cut at about 15,800ft (4,819m) in the exist- alone, but they reduce the push that must be supplied, delaying 3 1/2-in. tubing and hole drilled to a measured depth of ing the onset of buckling.


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Vibrating tools help, too. And larger tubing, either diameter and/or wall thickness, also extends the reach of CT. “There is a point of diminishing return, however,” Crabtree said. “As size increases, the weight that must be pushed also increases.”

MORE MICROHOLE R&D Accessing bypassed production in mature fields is a key opportunity for microhole drilling technology. But so is exploration, Gray said. In exploration, microholes offer the benefits of a small footprint that lowers location cost – roads and infrastructure. Casing, cement, mud, waste control and other costs are reduced, and impact on the environment can be minimized. Microhole drilling can be done where it might not be possible to move in conventional dr illing equipment. “Microhole drilling can drill, access and define new reserves in a very cost-efficient and environmentally-sensitive manner,” Gray said. Baker Hughes has developed thru-tubing drilling (TTD) technology with jointed pipe and CT. With its smart well intervention technology, it can put tools in the hole that

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monitor downhole conditions in a live well. Tools can pass through production nipples without having to pull a completion string and do remedial work without mobilizing a conventional rig, and do it safely without shutting in production. Baker Hughes has used the technology extensively in Russia where infrastructure is limited to exit casing underbalanced – milling a window – then drilling underbalanced. Considerable R&D effort is being applied to developing microhole technologies and CT drilling is an important part of this potential.

THE DOE’S ONGOING EFFORT Microhole drilling could be cost effective for shallow and moderate-depth holes for exploration, field development, long-term subsurface monitoring, and to a limited degree, oil and gas production, according to the U.S. Department of Energy (DOE). Late last year, the Gas Technology Institute (GTI) and the DOE announced the successful field-testing of a microhole drilling technology. The GTI and partners Rosewood Resources Inc. and Advanced Drilling Technologies have used microhole technology to successfully drill wells in the


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Niobrara Chalk reservoirs in Kansas and Colorado. develop self-expanding well casings to any diameter, “The benefits in cost savings (of microhole drilling) to the leading to improved methods and feasibility of mononatural gas industry alone could be $8.4 billion during a 15bore drilling and well construction. year period,” said Rhonda Lindsey Jacobs, project manager • Confluent Filtration Systems LLC (Houston) —Sand that for the National Energy Technology Laboratory (NETL). infiltrates the drillstring during microhole drilling can “The volume of drilling waste could be reduced by 103 milbe a problem, especially in small-diameter wellbores. lion bbl or to one-fifth the amount of waste volumes generThis project is designed to develop a concept for a selfated while drilling conventional wells. These targets are expanding, high-flow sand screen that could be made worth the government’s investment.” from a wide range of materials. Early last year, the DOE announce R&D funding for 10 • Tempress Technologies (Kent, Wa.) —The goal is to develop new microhole technology projects aimed at pushing the techa small, mechanically assisted, high-pressure water-jet nology toward commerciality and widespread application.The drilling tool. A downhole intensifier would boost the initiative involves developing technologies associated with pressure. The tool would overcome the limited reliabil3 drilling wells smaller than 4 /4-in. in diameter and related ity, power and torque of small-diameter drill motors, a downhole micro-instrumentation. major hurdle for microhole drilling reliability. The projects will be managed by the DOE Office of Fossil Energy’s NETL.Total value of the projects is nearly $14.5 million, with the DOE contributing $7.7 million “LOCKUP CAN BE A SIGNIFICANT CHALLENGE WHEN and industry partners providing $6.8 million. An earlier USING COILED TUBING TO DRILL LONG HORIZONTAL round of solicitations under the DOE’s microhole technol- WELLBORE SECTIONS.” Ed Smalley, ogy initiative, announced in June 2004, involved six projSenior Vice President, CTES LP ects valued at nearly $5.2 million. In making the latest announcement, the DOE reported it expects widespread adoption of microhole technology to boost infill drilling and substantially cut • CTES LP (Conroe, Texas) —Researchers will focus on exploration cost and risk. The department recently estimated improving the performance and reliability of microhole the remaining shallow (less than 5,000ft – 1,525m – subsurCTD bottomhole assemblies while reducing the cost face) oil resource in the United States at 218 billion bbl. and complexity of drilling inclined/horizontal well secThe focus of the DOE’s work is on adapting conventional tions greater than 2,000ft (610m). Inducing vibration CTD techniques to ultra-small-diameter holes. A complete, along the CT drillstring would eliminate the need for a cost-effective microhole drilling system must include a full downhole tractor. spectrum of subsurface sensors, motors, logging tools and • Technology International Inc. (Kingwood, Texas) —This other borehole instruments small enough to fit into the project will develop and test an effective downhole micro-wellbores, yet rugged enough to survive the harsh drive mechanism and a novel drillbit for drilling with downhole environment. CT. The high-power turbodrill will deliver efficient The 10 new projects announced last year are: power at relatively high revolutions per minute and low • Geoprober Drilling Inc. (Houston) —This project calls for bit weight and use high-temperature cutters that can drilling three wells with a composite CTD system to drill hard and abrasive rock in 3 1/2-in. boreholes. confirm the capability to drill low-cost, shallow • Ultima Labs Inc. (Houston) —The goal is to combine existslim/microhole exploration wells in water depths to ing technologies for measurement-while-drilling and 10,000ft (3,050m). Cost savings are projected at 59% logging-while-drilling into an integrated, inexpensive compared with conventional wells. measurement system to facilitate CTD of small-diameter • Technology Institute (Des Plaines, Ill.) —A next-generation (3 1/2-in.) wells at depths shallower than 5,000ft. microhole CT rig fabricated by Coiled Tubing • Baker Hughes Oilfield Operations Inc. (Houston) — Solutions for drilling to 5,000ft will be field-tested. In a Researchers aim to provide a wireless system to help Kansas gas field last year, the rig was able to drill steer drilling in a microbore. Plans call for developing a between 280ft and 400ft/hour (85m and 122m). It downhole bi-directional communication and power could lower drilling cost/well by 28% to 38%, accordmodule and a surface CT communication link. ing to the DOE. • Gas Technology Institute (Des Plaines, Ill.) —The institute will • Confluent Filtration Systems LLC (Houston) — design, develop and evaluate a counter-rotating motor Researchers will seek to develop an elastic-phase, selfdrilling system ideally suited for reducing costs associated expanding tubular technology.The company’s goal is to with dr illing wells targeting unconventional gas.


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MAINTENANCE AND REPAIR

Versatility and Box of Tools make CT Ideal for Thrutubing Work Well maintenance and repair using a workstring and tools that can be deployed through production tubing has long been the most common application of coiled tubing technology. With new fit-for-purpose tools as well as sophisticated software and telemetry, coiled tubing can perform an increasing variety of re-entry operations more effectively.

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uch of today’s production comes from mature fields where operators have refocused on how to increase asset value by boosting production and recovery. Some of this gain will be made “with the drillbit,” but a growing share of the increase will result from intervention operations, said Alex Crabtree, product line technology manager for coiled tubing (CT) with BJ Services Co. Coiled tubing offers several advantages. The ability to circulate while treating a live well minimizes formation damage that can occur when a well is killed. Circulation also makes possible the use of flow- Roto-Pulse screen cleanout process uses Roto-Jet tool. (courtesy of BJ Services) activated tools. Coiled tubing allows faster trip times than conventional • cutting tubulars with fluid; drillpipe but still has the rigidity needed to access intervals in • pumping slurry plugs; highly deviated and horizontal wells, and apply tension or com• zone isolation; pression forces downhole. • scale removal (hydraulic); and In thru-tubing applications, CT can deploy a variety of • wax, hydrocarbon or hydrate removal. tools that may not necessarily be CT products. Much of the There also is a variety of mechanical well service operations advance in CT technology in recent years has been in reduc- for which CT is well suited, including setting a plug or packer, ing the size – at the same time maintaining the reliability and fishing, perforating, logging and mechanical scale removal. increasing the capability – of tools used for conventional jointed Tubulars can also be cut mechanically, sliding sleeves operated pipe operations. and completion equipment installed. The Intervention & Coiled Tubing Association (ICoTA) cites A steadily growing global fleet of CT units is routinely perthe following pumping applications of CT systems in existing forming most of these operations daily. wells: • removing sand or fill; CUSTOM DESIGN • fracturing and acidizing; As the application window opens wider, CT as large as 2 7/8-in. • unloading a well with nitrogen; is being used, for example, in the North Sea. It means bottom• gravel packing; hole assemblies (BHA) must be designed with increasing tensile

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load capacity, said Gordon Mackenzie, product line manager for thru-tubing intervention with Baker Oil Tools and ICoTA cochairman. The ability to handle increased loads and increasing torque has generated a new approach to tool design. More tools are being designed specifically for CT operations. Until the late 1980s, for example, thru-tubing fishing was done primarily with tools adapted from those used for slickline operations, Mackenzie said. To overcome the limits of these tools, Baker Oil Tools has custom-designed CT fishing tools, for example, with an external and internal catch for a slick or fishing neck profile. Once on the fish, the tool can be disengaged hydraulically for further cleanup, to come back out of the hole or to be re-engaged. In addition to scale removal and cement milling, CT is being used increasingly for cutting operations. One part of Baker Oil Tools’ research and development effort is focused on severing exotic materials in monobore and thru-tubing applications. Thru-tubing operations, including stimulation, also make use of tractors. Almost any fluid, even that which is pure nitrogen or nitrogen-charged, will dr ive Welltec’s tractor turbines very well, said Brian Schwanitz, vice president and general manager of Welltec Inc. “A very promising application of tractors is on offshore platforms where it is not possible because of weight or crane limits to deliver a coil of large diameter tubing that normally would be needed for a job,” he said. Smaller-diameter tubing – a lighter-weight coil – combined with a tractor can provide the same ability to reach the target as larger diameter tubing.

annulus to lift the sand to surface. The well, however, must be killed before reverse circulating. Weatherford’s CT focus is on intervention services. “We are doing more rigless operations, including both coiled tubing and wireline deployed tools,” said Michael Stulberg, global product line manager for thru-tubing with Weatherford. The company has made about 25 acquisitions to acquire its thru-tubing capability. “Not to minimize the role that each component or tool plays in applying a solution, but there are hundreds of tools available for intervention operations,” Stulberg said. “What each of these tools does independently of the others is irrelevant. It’s about the problems we can solve by screwing them together in various ways and creating the system that solves our client’s problems.” Well cleanout is still the largest component of Weatherford’s thru-tubing business. Remedial cementing, zonal isolation and stimulation activities are growing, however.Weatherford divides its thru-tubing intervention work into three solution categories: wellbore obstruction; wellbore departure; and wellbore isolation.

NEW CAPABILITIES Improved techniques, fluids and tools have boosted the efficiency of CT well cleanout operations. Because many wells now being

CLEANOUT: CT’S ENDURING STRENGTH Well cleanout – removing sand, proppant flow back, frac job screen-out and other solids that inhibit fluid flow – is one of the most common CT operations. Coiled tubing capability is keeping pace with the need to clean out deeper wells and longer horizontal intervals. Schlumberger set a depth record on Russia’s Sakhalin Island, for example, when it completed about 32,150ft (9,806m) true measured depth cleanout operations with 2 3/8-in. outer diameter CT using a downhole tractor to help reach the target depth. Roughly half of CT work is still well cleanout, according to one estimate. In many cases, the material can be circulated out up the CT/tubing annulus as a jetting nozzle on the end of the string penetrates the fill. If the material is more consolidated, it may be necessary to run a downhole motor and bit on the CT to remove the fill. Reverse circulation can also be used to remove In-tubing completion interventions use non-inflatable packer systems to perform various large amounts of material or when well geometry intervention completions services, such as velocity string, tubing patch, safety valve, gas lift does not permit a high enough flow velocity in the valve and jet pump installations. (Image courtesy of Weatherford)


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Halliburton’s SandTrap service uses resin technology to consolidate the near-wellbore area to help prevent sand production. The consolidated area maintains almost 100% of initial permeability.The system incorporates a solvent/resin mixture deposited as a thin film on the formation and clay surfaces. The solvent package provides a low-viscosity treating fluid and a way to get the resin in contact with the formation. A SandTrap treatment can be applied to new or existing sand completions and placed down production tubing with jointed pipe and a service packer, or with CT. Coiled tubing and SandTrap service can put existing zones back on production without the expense of a conventional workover rig. Relatively low-tech well cleanout operations using a nozzle and circulation are still one of the most frequent CT operations. More difficult cleanouts typically require rotation to remove scale, mill cement or remove bridge plugs. One of Weatherford’s recent developments is a new motor technology designed for more power, longer life and higher temperatures. The eCTD motor comes in sizes from 1 11/16 in. to 2 7/8 in.

PLUG REMOVAL “One of the biggest uses for coiled tubing in North America is re-entered with CT have much more complex trajectories and the removal of composite bridge plugs and frac plugs following geometries, understanding transport phenomena throughout the fracturing operations,” Mackenzie said. wellbore has become more critical – and the subject of current These operations typically require a downhole workover research, Crabtree said. motor and an appropriate BHA. Selective placement of treatment fluid to remediate gravel Multiple frac jobs are being done more frequently and more packs is a growing CT application. CT techniques can spot flu- quickly, and are being done throughout the United States, preids in specific areas to “excite” the gravel pack, for example, to dominantly in new gas field developments, Mackenzie said. allow fluids to enter and fines to be washed out without damagIn a typical multiple-zone fracturing application, the first zone ing the gravel pack or screen. BJ’s Roto-Pulse, for example, uses is perforated, a proppant or sand frac is performed then a comthe Roto-Jet tool with optimized operational parameters and posite bridge or frac plug is run.The next step is to perforate the nozzles to place fluid uniformly behind the screen across the next zone and frac it above the composite frac plug, and the entire interval and fully remove it. sequence is repeated. In many cases, the bridge plug and perfoNew indexing tools that allow orienting into multilaterals ration operation have been combined to allow for even greater have improved the “dexterity” of CT, said Dan Bohannon, vice economies of scale. president for CT and nitrogen services with Cudd Energy As many as 20 plugs have been deployed in a single well, Services. Motors used for cleanout can now withstand higher Mackenzie said, and Baker Oil Tools has milled 20 plugs in a sinpressures and temperatures. Gas motors are available to work on gle CT run. Average mill-out time for the plugs is between 15 formations that are fluid sensitive, avoiding the need to circulate minutes and 30 minutes. a full column of fluid. Since it provides plugs and milling assemblies, Baker Oil Tools Cudd has used gas motors with nitrogen and air. For economic has designed both to be compatible and able to be milled quickly. reasons and because nitrogen equipment was not readily avail- Its composite plugs have a clutching mechanism on the top and able, an air mist was used in the U.S. Four Corners area. Air is bottom to lock the clutches together when the center body and more corrosive than nitrogen, and in some situations, it can pose lower clutch guide of the plug being milled is pushed onto the well control risks. plug below. The design allows milling to continue in the most To avoid frequent sand wash operations, it is possible to lock economic manner. sand or proppant in place. An initial wash can be followed with a sand control treatment, for example, that treats the problem AN EXTREME CASE rather than the symptoms, said Perry Courville, manager for CT Scale can be a significant problem. In the BMB field in northand hydraulic workover with Halliburton Energy Services. west Poland, Polish Oil & Gas Co. has been successful in

This coiled tubing tractor unit has treating nozzles. (Photo courtesy of

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Welltec Inc.)



mechanically removing the scale deposits and restoring production using under-reaming technology conveyed on heavy-wall CT. BJ Services International BV used the system to clean three wells in the field using positive-displacement motors, mills and under reamers.The field is estimated to have recoverable reserves of 9.3 million tons of oil in the predominantly dolomite Zechstein formation, and 9.3 billion cu m of gas. The goal was to boost production by milling the iron sulfide scale from the 2 7/8-in. production tubing, then under-ream scale from the 7-in. perforated casing below the tubing shoe. The candidate wells selected for CT cleanouts were characterized by the hardness of the scale, high formation pressures and a hydrogen sulfide (H2S) environment.Wellhead pressures during operations were expected to exceed 300 bar, making the collapse pressure rating of the CT a key design criter ion. With sour gas content in excess of 15% in some areas of the field, safety was a top priority. The special 1 3/4-in. tapered string for the job was manufactured with 80,000psi yield material, rather than 90,000psi or higher, to reduce the risk of H2S embrittlement. An H2S inhibitor was also used in the base oil circulating fluid to help protect the string. The cleanout operations required an average of 4 1/2 days per well. Onsite CT monitoring and modeling software aided the clean-out operations. In one instance, CT weight during tripping did not match predicted weights; onsite modeling helped identify corkscrewed production tubing as the probable cause.

Though not developed specifically for CT, BJ’s “liquid stone” cementing technology has a synergy with CT operations, Crabtree said. For example, if squeezing off perforations or setting abandonment plugs, volumes tend to be relatively small. Cement can be taken to offshore or remote sites pre-mixed and ready to be pumped through CT. Quality control can be performed at the base before the cement is sent to location.

STIMULATION: MULTI-FRACS AND CT The CT stimulation market is large; one estimate puts it at about $100 million per year. Coiled tubing fracturing has seen significant growth in recent years, fueled by improvements in fracturing technology and fluids. Much of the work is in shallow gas development in Canada. Multiple frac jobs are also a typical treatment in the Bar nett shale in the United States; some are done with CT, some are not. Most CT frac jobs are performed on recently drilled wells that require multiple small fracs rather than a massive frac. The need to expose the zone to be stimulated while isolating the zone that has just been stimulated can be met by CT’s speed and versatility. The ability of CT to move in and out of the hole quickly makes it an attractive tool for fracturing and acidizing, especially when treating multiple zones in a single well. Coiled tubing can accurately spot treatment fluid and provide uniform treatment of long horizontal intervals. BJ Services’ OptiFrac, for example, can perform a typical multi-zone frac in less than a day.The service features adjustable straddle lengths, increased depth, lower cost and other benefits. It can be configured for 4 1/2 -in. and 5 1/2 -in. casing and can be made available for 7 in. An earlier concern that proppant might erode the CT string and shorten its life has been mitigated by monitoring wall thickness during the job, according to ICoTA.The measurements can be used to adjust the CT fatigue models and accurately determine remaining CT string life.

REMEDIAL CEMENTING, ZONAL ISOLATION For Baker Oil Tools, zonal isolation means bridge plugs for temporary or permanent zone isolation. Permanent applications typically are to shut off gas or water in a lower zone, or for field abandonment.Temporary applications include installing a bridge plug as a workover barr ier, for wellhead maintenance or to evaluate upper zones. “Coiled tubing can be used to set a retrievable bridge plug for any application,” Mackenzie said. “All the tools can operate without set-down weight or rotation for either removal or setting.” Coiled tubing can also be used to place water conformance chemicals to shut off upper or intermediate zones with a fluid rather than cement. With the acquisition of Zertech, Baker Oil Tools added to its range of zonal isolation solutions.The company’s technologies span from a monobore environment where there are next to no expansion requirements, through the metal-to-metal seal capability with expansion to 160%, to the industry’s highest expansion capabilities with nitrile elastomeric inflatable tools. Inflatable operations thru-tubing can With coiled tubing, CobraMax service and Hydra-Jet create perforations and initiate fractures. (Graphic courtesy of Halliburton) achieve up to 350% expansion.

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Sophisticated electronic monitoring ensures exact location and load calculations for placement-critical operations. (Photo courtesy of Schlumberger) Growing emphasis on the benefits of “pinpoint stimulation,” an objective facilitated by CT’s ability to move up and down the hole quickly and easily, is driving growth in fracturing with CT, Courville said. More new units are equipped with larger tubing for this application. Ten years ago, 1 1/2 -in. CT was typically used to clean out 3 1/2 -in. tubing, for example. Now 1 3/4 -in. or 2-in. tubing is used to achieve the flow rates needed for fracturing. Larger tubing then requires larger reels and redesigned injector heads. Being able to perform multiple fracs in one day is attractive. “It’s common to do eight fracs in a day in one well, then move on to the next well,” Courville said. Its CobraMax fracturing service combines the performance of conventional thru-tubing fracturing and the speed and versatility of CT operations, according to Halliburton. It requires fewer trips in the hole and to the well site, and occupies a smaller operating footprint. The service can cost-effectively stimulate multiple zones that require larger, higher-rate treatments than are possible with conventional CT fracturing. Cobra Max’s high performance in multi-interval vertical wells


comes from optimizing injection rate, proppant volume and proppant concentration. The process involves pumping through conventional CT to create perforations and initiate fractures.The main fracture treatment is pumped concurrently through the CT/casing annulus.

STIMULATING A GAS STORAGE WELL Late last year, BJ Services completed a CT stimulation operation on an underground gas storage well in Grijpskerk near Groningen, The Netherlands, that is owned by Nederlandse Aardolie Maatschappij (NAM), a 50-50 Shell-ExxonMobil joint venture, and operated by Shell Exploration and Production. The goal was to increase the production and injection rate of the 7 5/8-in. gas storage well using acid stimulation to restore the well’s capacity to 6 million scm/d. Declining performance during several years indicated scale, fines or drilling damage in the well. The well was partially completed with 7-in. and 7 5/8-in. tubing, a 7-in. blank liner and 7-in. pre-packed screens from 10,735ft (3,272m) to 11,293ft (3,442m). A pre-packed screen, an acid screen-wash and mud-acid

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squeeze was proposed, but there were several concerns about the operation: • the acid resistance of the pre-packed screen, mesh wire and pre-packed Bakerbond sand; • potential damage to the mesh wire by the jetting impact during the screen wash; and • potential damage to surface equipment from oxygen and chlorides in the treatment fluids. BJ tested samples of the screen using the proposed treatment recipes to determine the required corrosion inhibitor loading. A microscopic examination of the mesh wire following a 12-hour soak in the acid at bottomhole temperature showed no damage to the screen. To reduce the impact pressure on the screen while retaining optimum screen coverage, BJ considered using its Z-Seal is a metal-to-metal sealing technology. (Image courtesy of Baker Oil Tools) Roto-Pulse tool. Because the treatment would be pumped using nitrified fluids to remain within frac job, Bohannon said. It can be accurately oriented to the collapse limits of the CT, the Phase Separator was introduced fracture or any direction the geologist feels will result in the to further reduce the impact pressure by separating the nitro- best fracture growth. gen from the fluid just above the Roto-Pulse tool. No damage was sustained by the mesh wire or to the pre-packed sand dur- GOING ‘ROUND THE BEND ing the tests using the Roto-Pulse and jet nozzles. In the age of routine high-angle wells, some angles build quickly To prevent oxygen from appearing in the produced fluids, and can pose a challenge when attempting to run a long peracid was mixed with nitrogen instead of air and an oxygen forating gun or other long BHA. It is important to know before scavenger was added to the recipe.To lower the chloride con- going in the hole whether the tool can be moved past a signiftent of the fluids before they entered the production system, BJ icant change in hole direction or dogleg, and if so, how large a pumped oxygen-free water into the flow lines, a process that bending force will be subjected to the tool. required considerable preparation. CTES has developed “tool-fit analysis” software based on The CT intervention was completed in 6 days and boosted finite element analysis to answer these questions. Input to the production from 4.5 million scm/d to 6.5 million scm/d, a rate program includes material yield strength, tube outer diameter higher than the well’s initial performance. and inner diameter, and the wellbore trajectory either proposed or actual. PERFORATING AND RE-COMPLETION The software will also analyze the effect of adding centralizers Perforating with CT is an expanding application, especially in or rollers on the BHA, and help determine optimum placement. horizontal or high-angle wells. BJ has used various deployment “The results from these modeling efforts are not always systems to run sections of perforating guns as long as 3,000ft obvious,” said Ed Smalley, senior vice president of CTES LP. (915m) into a well and out of a live well in one run. “For example, the addition of knuckle joints may actually make Cudd’s work in horizontal intervals includes a growing it more difficult for the BHA to navigate through a dogleg. number of “tunnel” perforating applications, Bohannon said. “It’s a big help in ‘designer wells’ for determining what This older concept has been revived as CT technology has downhole tool configurations can successfully negotiate developed. doglegs and herring-bone drainage patterns. If done in the In tunnel perforating, a plug is set when the CT reaches planning stage, a minor change in wellbore trajectory that is depth, then a gelled sand is mixed and pumped to jet cut a tun- acceptable from a reservoir development standpoint, for nel out into the formation. Operators report the operation pro- example, could make future well intervention operations vides greater reach into the formation and a more predictable much easier and much less costly.”

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SUBSEA INTERVENTION

Solutions take Shape for Subsea Intervention If there is one market segment that poses the biggest challenge to coiled tubing technology, it is subsea intervention. Currently, it is a commercial challenge, too, although that eventually will change.

S

ubsea intervention with coiled tubing (CT) requires a boat, a coil and a riser, making it a process that necessarily involves several companies. It has been difficult to put all these elements together in one place, in part because the market is not yet large enough. Studies are under way, including some joint industry projects, aimed at developing the best way to exploit CT’s potential for subsea well intervention. “The challenge is to get enough players in the market – and to expand the market – so it becomes profitable,” said Perry Courville, manager for CT and hydraulic workover with Halliburton Energy Services. A recent forecast projected there would be 4,000 subsea wells by 2008. It is inevitable that the frequency of workover needed for these wells will increase, and even though many of these wells were planned and drilled to minimize the need for intervention, there is evidence that workover frequency will be higher than expected. The result is a g rowing industry-wide interest in how to costeffectively intervene in subsea wells, said Warren Zemlak, Schlumberger business development manager for CT services, and Schlumberger has several efforts “in the design phase.” There is a need for a rigless subsea intervention technique, he said, but the challenges are significant and there is a lot to be done. “Today, the solution is to bring back the rig, but current demand for rigs and the cost of rig time both challenge an operator’s ability to fix an existing subsea well,” he said. Coiled tubing skid equipment is on an offshore platform.

DIFFERENT PATHS, SAME GOAL When operators initially forecast reserves discovered by land wells and dry trees on offshore platforms, they might expect various interventions for stimulation or sidetrack drilling during the well’s life to increase that reserve by 50% to 80% “Why should subsea wells be different?” goes the thinking, said Alex Crabtree, product line technology manager for CT with BJ Services Co. “How can we apply the intervention techniques we’ve been using on traditional wells to subsea wells to bring those same reserves increases?” Most subsea wells are still young, and the need for intervention has been limited, but that will change. How quickly it will change is difficult to forecast, Crabtree said, making it hard to determine the right time to spend capital to be prepared. During the past few years, a number of solutions have been


(Photo courtesy of Halliburton)

proposed and projects started that would make subsea intervention practical and cost effective, including conversion of jackup rigs, or new fit-for-purpose semisubmersibles or monohull ships. The range of these approaches is broad because of a variety of subsea well types, depths and production systems. “Though subsea intervention faces both technical and commercial challenges, it will be a growth area for all facets of the industry, coiled tubing included,” Crabtree said.

BIG SAVINGS POSSIBLE Earlier, ExxonMobil Corp. announced the development of the Subsea Intervention Module (SIM) to significantly reduce the cost and time of downhole logging, acidizing and

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SUBSEA INTERVENTION

Specially designed coiled tubing units have found increasing applications offshore. (Photo courtesy of Cudd Energy Services) other interventions in deepwater wells. According to ExxonMobil, the system could perform these activities up to three times faster than a mobile offshore drilling unit and save as much as 50%. The SIM design consists of a 380-ft (116-m) long vessel with a specially designed intervention tool that is lowered to the seafloor and latched onto the subsea well.The SIM tool will be functional in up to 6,500ft (1,983m) of water and be able to accommodate well depths to 13,000ft (3,965m) below the seafloor. The system is designed for use in wells employing horizontal subsea trees with 36-in. structural casings. As planned, the SIM vessel would be a dynamically positioned ship, about 1 1/2 times the size of a standard offshore stimulation vessel. It would feature a large moonpool for deployment of the intervention tool, a mission control center and accommodations for a crew of more than 100. SIM is a very interesting and exciting opportunity for CT, said Dennis Dunlap, president of the CT business unit with

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Precision Tube Technology. “It’s a game changer technology for servicing deepwater wells.” Statoil has made considerable progress with thru-tubing rotational drilling operations in subsea wells, operating from mobile drilling units. Last summer, it successfully completed the first subsea thru-tubing rotary drilling and completion operation. Statoil is exploring the possibility of deploying thru-tubing drilling from smaller and more cost-efficient vessels. Coiled tubing is of interest in this context, according to Statoil, since it could allow drilling from lighter ships without a drilling derr ick. Statoil has said the development of a fit-for-purpose dynamically positioned vessel for subsea thru-tubing dr illing could save $20 million per sidetrack compared with a conventional semisubmersible.Vessel size would depend on requirements for mud handling and production testing. Such a unit would need high capacity data transmission capability, superior steering capabilities and might make use of composite CT, according to Statoil.


SUBSEA INTERVENTION

PLATFORM STACK STRESSES In addition to growing interest in CT intervention in subsea wells, use of longer and more complex intervention stacks on floating structures has posed new questions about equipment selection and safety. When a CT intervention unit is operated from a tension-leg platform or spar, for example, the wellhead on the platform moves independent of the platform.The intervention riser must be connected to the wellhead so the well can be entered under pressure, but the other end is anchored to the independently moving platform.Tall intervention stacks are more susceptible to bending forces from crane, production riser and platform movements. Proper equipment selection, how to best support the riser on the platform and minimize stress in the riser, are important questions to be answered when designing the intervention stack. In the past, the allowable movement, when to add supports and when to halt operations were judgment calls. CTES’ Zeta system is designed to eliminate guesswork and optimize stack configuration. “The Zeta-Model enables users to make informed decisions regarding the need for a gimbaled table or titanium lubricator sections,” said Ed Smalley, senior vice president of CTES LP. For pre-job modeling, Zeta will determine: • probability of exceeding pre-set safety limits during operation; • need for additional intervention stack supports and their location; • stress changes as a result of stack loading changes; • maximum stress location; • weight required to buckle the stack; and • an optimized rig-up configuration. For monitoring dur ing the job, CTES has developed a 2ft (0.6-m) long lubricator section instrumented with fiber The Zeta screen capture shows stack stress in blue. (Image courtesy of CTES) optic strain gauges installed as part of the intervention stack. Fiber optic strain gauges are required to provide the necessary the technology to a group of wells or campaign to extend the measurement resolution. An added benefit of these strain learning curve, realizing there may well be problems to overgauges is that no electricity is required at the wellhead. The come. Zeta-Gauge is at or near the point of maximum stress in the “That’s been the approach in some of our operations in stack to determine the impact of changing surface, downhole Oklahoma, in Alaska and in Sharjah,” Mackenzie said. or offshore conditions. Coiled tubing’s history is rooted in its use as a cost-effective “Real-time Zeta monitoring during an operation allows the well cleanout tool. In recent years, these conventional wellbore operator to decide when to suspend operations based on real data, cleanouts and acid stimulation jobs accounted for more than rather than guesswork,” Smalley said. three-quarters of total CT revenue. However, CT fracturing and drilling applications have emerged as two of the fastest growth areas. Revenue from these WHERE COILED TUBING IS HEADED Coiled tubing drilling has had a cyclical history. Often, an two CT applications has grown from almost zero 10 years ago, operator would use CT drilling on one job, and if results were to about 15%, according to ICoTA. questionable, the technology would not be used again until The CT market is dominated by the three large service comrecommended by a new department or manager. panies, which control about 60% of the CT market. On a regional Like any emerging technology, that’s not the optimum approach, basis, according to ICoTA, there are typically more than 30 said Gordon Mackenzie, product line manager for thru-tubing providers of CT in the international market; Canada is served by intervention with Baker Oil Tools and Intervention & Coiled more than 35 CT service providers, and the United States by Tubing Association (ICoTA) co-chairman. A better test is to apply more than 25 companies.

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SUBSEA INTERVENTION

Once Gulf of Mexico activity returns to pre-hurricane levFAST GROWTH CONTINUES Last year, roughly 100 new CT units were added to the fleet, els, there will be more gravel pack work, Bohannon said.A lot of Courville said, and he expects a similar number of units to be the wells shut in by Katrina may have sanded up and will have added this year, though manufacturing capability is currently to be worked over. restricting growth. “There’s going to be a lot of work in that area,” he said. “We don’t see any slowdown in activity in the near term,”he said. Cudd was in the process early this year of training people and “The fastest growth will be in stimulation and fracturing.” had three new CT units ready when work resumed in the Gulf. In the near future, growth in applications for CT will outstrip This will be another “solid” year for CT growth, said Dunlap, the conventional drilling market, said Jimmy Gray, Baker Hughes much like last year. To meet that expected demand, Precision Inteq product line manager for slim hole reentry systems.Though there will be additions to the conventional rig fleet, there will continue to be limited availability of conventional rigs for some time. The ability of CT operations to boost production will be the main driver of that growth, Gray said. “The goal is to more effectively drain the reservoir. Accessing reserves that are known to exist but to date have not been able to be produced will be the biggest market for CT drilling,” he said. Cudd currently is focused mainly on intervention – for cleanout, multi-frac bridge plug removal, for example – but is moving to larger pipe sizes to expand its CT drilling and stimulation capability. Cudd also expects CT drilling to be the application with the fastest growth. As opportunities for CT expand, fluid technology will become more important. “Expertise we’ve brought to the company has increased our coil life through a better understanding of what is needed to inhibit fluid being pumped,” said Dan Bohannon, vice president for CT and nitrogen services with Cudd Energy Services. Cudd is also building larger pumps to be able to pump higher rates at high pressures. “But the volume of work we have now does not give us much opportunity to explore new applications,” Bohannon said. “We could not do much more work than we are doing now and still keep our units maintained.” This high utilization rate is despite the recent addition of new units in the Rocky Mountain region and the Permian Basin, and more units are scheduled for delivery. By December, Cudd expects to put three more units to work; next year, it plans to add six or An Inteq engineer inspects the CoilTrak advanced coiled tubing directional drilling bottomhole assembly after completion of a successful multilateral drilling run in Alaska. (Photo courtesy of Baker Hughes Inteq) seven more units.


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SUBSEA INTERVENTION

executed a major expansion of its plant this year, boosting manufacturing capacity by 50%.

MORE LONG, LARGE STRINGS Dunlap expects part of the growth in CT work will be in deepwater wells, an application for which Precision is furnishing an increasing number of long strings. For example, measured depth could be 25,000ft (7,625m), water depth 5,000ft (1,525m) and the service company will want a little backup length. “All of a sudden, that turns into a 32,000-ft (9,760-m) string of coiled tubing,” Dunlap said. “We’re seeing more of these strings – we’re counting them on two hands now – and more discussion of this application.” Precision has manufactured these strings, and it made a 27,000-ft (8,235-m) coil of 2 7/8 in. that is the company’s heaviest at about 70 tons. Precision also supplies CT for small diameter subsea pipelines. A number of operators have recognized the advantage of supplying pipelines in long continuous lengths with continuous external coating, Dunlap said. A typical pipeline application might be a 24-in. pipeline where a 2-in. methanol line is also needed. To piggyback the 2in. CT on the 24-in. line is easier than putting a separate welding line and handling system on a lay barge. “We’re seeing a number of these applications,” Dunlap said. Coiled tubing is being increasingly used for methanol injection service. Precision supplied the monoethanolamine injection system for Statoil’s Snøhvit project offshore Norway, for example. Compared with jointed pipe, CT is usually cleaner on the inside, an advantage in a methanol system where needle valves and filter systems can easily become clogged. “Expected growth in coiled tubing activity is 15% to 20%, and that will put a strain on the industry. That growth also poses a bottleneck in industry’s ability to absorb new coiled tubing technologies,” Zemlak said. It also is an opportunity to invest more in game-changing technology.The CT drilling and intervention envelopes continue to be pushed, for example, as horizontal displacements get longer. Schlumberger recently reached new depth records in CT drilling with a total measured depth (TMD) of 18,200ft (5,551m), and in intervention applications, which included a TMD of about 32,150ft (9,806m) with 2 3/8 in. outer diameter CT. In expanding its capability, BJ Services will create synergies between other product lines and its CT services to deliver value in its intervention work, Crabtree said. It also will continue to develop new technology tailored specifically to CT operations. Fluids will be one focus, since most work is still done with small tubing sizes – 1 1/2 in. and 1 3/4 in. – in which friction pressure during pumping operations can be high.The challenge is to develop fluids that can perfor m well not only during stimulation or cleaning operations, but also will have a lower friction that allows higher pumping rates.

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“Ensuring pipe performance in sour wells is also a growing issue,” Crabtree said. BJ is part of an ongoing project with ExxonMobil and Shell Canada to investigate performance of CT in well intervention operations in hydrogen sulfide environments. An indication of the maturity of CT operations is the increase in “regulatory” work in relation to CT, Crabtree said. The American Petroleum Institute, where working groups are focused on well control and tubing itself, is developing recommended practices and standards. Working groups in Canada are also developing recommended practices.

CHALLENGES TO GROWTH Expected growth in CT activity poses a significant people challenge, Zemlak said. “Personnel development has become an essential priority for us. Competency and proper training are increasingly important,” he said. Maintaining commitment to internal training, Schlumberger continues to invest in its training centers. Advanced methods of training in the field, such as computer-based field simulators available in virtually every Schlumberger CT operation, are also being incorporated. Schlumberger also offers CT training to customers, and the company has seen a significant increase in requests for advanced level training, said Zemlak, and has seen a significant increase in requests for advanced level training. One of the largest restrictions to growth in the current cycle of high oil/gas prices and demand is limited resources of personnel and equipment, Mackenzie said. A threat to the further growth of CT as an intervention technique is a shift to positioning downhole equipment in highly deviated and horizontal wellbores with electric wireline and a tractoring system. “This technology removes the effective monopoly that CT once held in live well conveyance in deviated and horizontal wellbores,” Mackenzie said. As the trend to high-pressure, high-temperature (HP/HT) environments continues, intervention tools and systems will be needed with capability beyond what is available, especially in service life. Baker Hughes’ high-expansion metal-to-metal Z-Seal technology is an example of what will be needed for more extreme pressures and temperatures, and for chemical compatibility. Exotic materials being used to complete HP/HT wells will spur research and development on downhole cutting structures. “Smart” intervention technology using coiled tubing is also likely to become a differentiating technology, Mackenzie said.As operators require more and more real-time, two-way communication, the development of smart technology that does not require running electric wireline within the CT string will likely accelerate. HP/HT, low bottomhole pressures and exotic power fluid requirements are all trends that will lead to the continued evolution of non-elastomer ic CT workover motors with increasing capability.

www.eandpnet.com • November 2006 Copyright, Hart Publications, 1616 S. Voss, Suite 1000, Houston, TX 77057 USA • (713)993-9320, Fax (713) 840-8585

Advances in Coiled Tubing Technology E&P Supplement 2006

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