DOP 205 - Rev 6

Drilling Fluids Document No.

Document Title

DOP 205

Drilling Fluids

Page Rev No Date Doc No

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1 of 21 6 28.01.00 DOP 205

TABLE OF CONTENTS

1.0 2.0 3.0 4.0 5.0 5.0 5.1 5.2 5.3 5.4

PURPOSE...................................................................................................... 2 SCOPE........................................................................................................... 2 RESPONSIBILITIES...................................................................................... 2 DEFINITIONS.............................................................................................. 2 PROCEDURE................................................................................................ 2

6.0 7.0

REFERENCES........................................................................................... 16 ENCLOSURES........................................................................................... 16

Drilling Fluids.......................................................................................................... 2 Drilling Fluids Classification.................................................................................... 5 Drilling Fluid Field Tests....................................................................................... 11 Solids Control....................................................................................................... 13 Corrosion Control................................................................................................ 15

Rev No

Date

Prepared by:

Verified by:

4

21.01.98

KJO

WVE / ICO

Approved by: QA and Safety Managers AJE

5

12.03.99

IMI / LVA

ICO

AJE / BNO

6

28.01.00

IMI / LVA

ICO

AJE / BNO

G:\Management Library\Drilling Operations Manual\DOP 200\DOP 205

Reason for Revision As per Revision Request 001/96 As per Procedural Review Scheme Re-issued for implementation

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PURPOSE The purpose of this procedure is to describe and give guidance on drilling fluids and solids control.

2.0

SCOPE This procedure applies to all Stena Drilling’s Units.

3.0

RESPONSIBILITIES

3.1

Senior Toolpusher The Senior Toolpusher is responsible for the implementation of this procedure.

4.0

DEFINITIONS N/A.

5.0

PROCEDURE

5.1

Drilling Fluids Drilling Fluids are a large subject in themselves and it is beyond the scope of this procedure to consider them in extensive detail. The nature of drilling fluids and procedures required to handle and treat them are changing. This is due to further research being carried out to find effective and economical fluids. There is the need to develop drilling fluids which will withstand the extremes of temperature and pressure in deep, hot holes. There is the need to limit and eventually prevent damage to the environment. This section is an attempt to give information that will aid understanding of drilling fluids and consider procedures that will be required to obtain environmentally friendly and economical solutions. •

Drilling muds consist mainly of three parts :1.

The liquid phase (water or oil).

2.

The reactive part (colloidal portion)-chemicals, clays etc..

3.

The inert part - sand, weighting material etc..

Treatment of drilling muds is aimed at the colloidal portion as this is where the mud can be improved by chemical treatment, or is damaged by contamination.


Drilling Fluids •


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The drilling fluid has at least ten important functions :1.

Removal of cuttings from the bottom of the hole to surface.

2.

Cooling and lubrication of the bit and drill string.

3.

Coating the hole with impermeable cake.

4.

Controlling downhole pressures.

5.

Suspending cuttings and weight material when circulation is stopped.

6.

Releasing sand and cuttings at surface.

7.

Supporting part of drill pipe and casing weights.

8.

Reduce to minimum any adverse effects on formation adjacent to the hole.

9.

Assist in obtaining information about the formations drilled.

10. Transmitting hydraulic horsepower to the bit. Samples A sample must be taken from the bulk manifold sampling cock during the loading of all drilling fluids. Samples to be retained until the end of the well. 5.1.1

Cuttings Removal The face of the hole and edge of the Bit are cleaned by the jetting action of fluid flowing from the Bit nozzles. The fluid being circulated up the well carries the cuttings towards the surface. The cuttings tend to sink through the fluid under the influence of gravity. The speed of this “sinking” is known as the Slip Velocity. As long as sufficient mud is circulated fast enough to overcome this effect, the cuttings are brought to surface. Hole Cleaning depends on several factors: Velocity The annular velocity is an important factor in getting cuttings to the surface. This is dependent on pump capacity, pump speed, hole size and drill pipe/drill collar size. It is necessary to balance several factors when determining circulation rates. Too high a circulating rate will lead to annular velocities around the Drill Collars being greater than the critical velocity. This will then lead to hole erosion (washing out). The Critical Velocity is dependent on mud properties. Too low a circulating rate will lead to the hole not being cleaned. It is important to consider the effects of larger annuluses (e.g. drill pipe in marine riser). It can be seen that when drilling small diameter hole (8½" & 6") that it may be necessary to boost the riser to ensure that cuttings are lifted. Density


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This will have a buoyant effect upon the particles. Increasing mud density increases carrying capacity both by buoyancy and solids interference. Viscosity This depends on the concentration, quality and dispersal of the suspended solids in the mud. 5.1.2

Cooling And Lubrication Heat is generated by friction in the bit and by contact between the drill string and the hole sides. This heat is absorbed by the circulating fluid and released at surface. Lubrication is improved by use of emulsifying agents and lubricants.

5.1.3

Wall Building A good drilling fluid will deposit filter cake on the side of the hole to strengthen the formation and reduce fluid passing into the formation. This is achieved by treating the mud to improve solids distribution and fluid loss reduction.

5.1.4

Control Of Downhole Pressures This is achieved by use of mud density. Normally, the weight of water plus the solids picked up from drilling is sufficient to balance normal formation pressures. Abnormal formation pressures require the addition of mud weighting materials such as barite to increase the hydrostatic head of the mud column. This is discussed in greater detail in the Ref: Well Control Manual WCO 200.

5.1.5

Cuttings Suspension/Release Cuttings being carried to surface are held in suspension by gelling or thixotropy which develop well after circulation has stopped. When circulation resumes, the mud returns to its fluid condition and the cuttings are carried to surface. Cuttings are then broken out using solids control equipment.

5.1.6

Weight Support The weight supported by surface equipment becomes increasingly important with increasing hole depths. Since the drill pipe and casing are buoyed up by the drilling fluid, then an increase in mud density will result in a reduction in the total weight that the surface equipment must support.


Drilling Fluids 5.1.7


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Hole Information It may be necessary to adjust mud properties to improve data gathering. For example, addition of oils to lubricate the hole may be forbidden as it interferes with the work of the Well site Geologist. Treating mud resistivity properties to improve the interpretation of electric open hole logs are another area.

5.1.8

Transmit Hydraulic Horsepower To The Bit The drilling fluid is the medium for transmitting available power at surface to the bit. Flow properties of the mud, plastic viscosity and yield point exert a considerable influence on hydraulics and need to be controlled at proper values. All the factors need to be balanced to ensure that the optimum power is available at the bit to clean the face of the hole.

5.2

Drilling Fluids Classification There are many types of drilling fluid in use and new types are constantly being developed. They can be classified into groups as follows:

5.2.1

Water Base Fluids Fresh Water Muds - Little Or No Chemical Treatment Required •

Spud Muds - bentonite or clay mix, sometimes mix water must be treated with soda ash or lime. Generally used offshore to sweep hole as a pill whilst drilling with sea water and dumping returns.

•

Natural Muds - result from formations containing good mud making clays. In most cases, the natural mud will be chemically treated and become one of the treated muds discussed below.

Chemically Treated Muds - No Calcium Compounds Added •

Phosphate Muds - usually limited to areas with soft fresh water and good mud-making formations. These would generally be used in relatively shallow wells (7500ft or less) as phosphates cannot withstand temperatures above 180ºF, and are not effective when contaminated by salt or calcium.

•

Organic Treated Muds:

•

1.

Quebracho and other extracts - these are more resistant to contamination and higher temperatures than phosphate muds. However they have been largely replaced by other types of organic treated muds.

2.

Chrome Lignosulphonate - have been successful in wells with 400°F bottom-hole temperatures and have low reactivity with formation clays.

Calcium Treated Muds - the use of lime, gypsum or calcium chloride is no longer so common as these muds have been replaced with lignosulphonate muds due to their better reaction to high temperatures etc.


Drilling Fluids •

•

5.2.2


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Salt Water Muds - these will be the most common types of water base drilling fluid in use offshore :1.

Sea Water Muds - combined with polymers.

2.

Saturated Saltwater Muds - combined with polymers and used for drilling massive salt beds or domes to prevent hole enlargement due to salt being dissolved in a non-saturated mud.

Oil-Emulsion Muds (oil-in water) - these are a water base mud with oil mixed so that the oil is suspended as individual droplets in the water phase of the mud. These muds are effective in improving hole conditions, reducing torque and improving bit life as they offer better lubrication than water base muds.

Oil Base Fluids These Have Many Applications And Have Many Advantages •

Good protection and reduced damage to producing formations.

•

Good for drilling deep, hot holes as mud is more stable.

•

Reduce problems associated with differential sticking.

•

Reducing severe drill string corrosion problems.

•

Drilling troublesome shale formations.

•

Reducing Friction i.e. Torque and Drag particularly in directional wells.

The main disadvantage of using oil base fluids is containing them to prevent environmental damage and the need to clean and treat drilled cuttings before disposing of them. They also present additional problems for Well Control as gases are more readily absorbed into solution and then break out higher up the hole. Ref. Well Control Manual WCO 200. Procedures For Use Of Oil Base Muds (OBM) It is essential that the loss of OBM to the hole and the environment is kept to a minimum. The following priorities should be observed :•

Safety.

•

Environmental Protection.

• Operational Progress. Safety •

Safety clothing should be worn to minimise contact with OBM/Base Oil products. This should include the use of barrier creams to protect areas


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such as hands/arms which will be most at risk. Refer to Product Data Sheets for detailed information on the products in use. This information should be available from the Service Mud Engineer or the Medic. •

Ensure that personnel designated to use equipment with OBM such as Mud-Vac Units, High Pressure Wash Down Guns using Base Oil are properly instructed in their use and that relevant precautions are observed.

•

Spillage of OBM in working areas is to be minimised. The use of a Mud Saver Valve is recommended to avoid spillage during connections. Any spillage’s should be dealt with immediately using Mud-Vac etc.

Environmental Protection It is essential that procedures are developed to manage the use of OBM/Base Oil on the installation. These procedures must address several areas :•

Prevent spillage of OBM/Base Oil from the unit.

•

Monitor volumes of OBM/Base Oil onboard and account for all parts of the system. Any discrepancies must be investigated immediately and corrected before continuing with operations. These must be reported to OIM, Senior Toolpusher and Operators Representative.

•

Oil entrained with drilled cuttings must be monitored as required to ensure compliance with guidelines/legislation. The use of cuttings cleaning equipment may be required for certain types of OBM’s.

The following are guideline procedures to assist in developing Installation Specific Procedures for Oil Base Muds and Base Oils: Preparations For OBM •

Loading or Backloading of Oil Base Mud must be carried out under Permit to Work.

•

No OBM should be off loaded from the supply boat until all pits have been cleaned and pit dump valves and main dump valve closed and Tie wraps or plastic chain installed on valve handles, also no OBM should be held in the sand traps until the water base mud section of the hole is completed.

•

Check the integrity of all dump valves, mud mixing system valves, loading system valves and hoses.

•

Check out mud saver/containment systems on the unit. Ensure that valves are properly set up to route OBM to the recovery tank and not to dump. Test any pumps and alarms which may be part of this system. Check seals on the mud bucket in case it is necessary to pull a wet drill string.

• •

Close and lock-off all dump valves etc. to prevent inadvertent dumping and loss of OBM.


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It is recommended that heavy duty tie wraps or plastic chain is used for this. In the event of an emergency such as a fire, when the mud pits might have to be dumped in a hurry, then the tie wraps or plastic chain can be broken. Keys to the padlocks should be kept by both the S.T.P. and OIM. It is recommended that dump valves are only unlocked and operated under the permit system when the OIM and S.T.P. are satisfied that the tank contents to be dumped will not create a pollution hazard. •

To avoid water contamination of the oil base mud, it is recommended that all water lines in pump room, shaker house above pits and flowlines are isolated/plugged as required. Any mixing pump packings lubricated by water should be converted to grease lubrication or alternatively fitted with a mechanical seal.

•

Ensure that adequate supplies of protective equipment are available for personnel who will come into contact with OBM/Base Oil.

•

Ensure that Mud-Vacs, Washdown Guns etc. are set up, tested and personnel receive proper instruction in their use.

•

Order and fit any mud saver valves required to the DDM to minimise spillage during drilling operations.

•

Areas around mixing pumps, main mud pumps, possum belly tank shaker house and rig floor to be bunded and sealed to ensure that OBM returns to central collection tank. Mousehole drain to return to system.

Loading/Backloading OBM/Base Oil •

Establish the quantity of Oil Base Mud and Base Oil to be loaded and ensure that all personnel involved in the operation are fully briefed. Confirm with the Supply Boat Master regarding the sequence of operations, the volumes of base oil and oil base muds that he is carrying and an estimation of the volumes left on the boat after the operation is completed.

•

It is customary for Oil Base Mud to be loaded direct to the Mud Pits and for Base Oil to be loaded direct to its designated storage tank. It is recommended that the Base Oil is loaded first to avoid any chance of oil base mud being loaded into the tank. This will avoid the chances of solids settling out and the tank having to be cleaned.


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•

Consideration should be taken when operating within Areas of Environmental Sensitivity with a view to this operation being carried out during daylight hours only. At all other times, if it is required to carry out the operation at night, an assessment should be made of the overside rig lighting and it should be established that there is sufficient artificial lighting at the manifold and the area between the rig and the supply vessel to ensure that any leaks are readily identified.

•

Flotation jackets should be fitted to all bulk hoses used for the transfer of OBM and any other oil cargoes.

•

Prior to commencement, ensure that proper communications are established between the parties involved in carrying out the operation. Recommended personnel :1.

Master/Barge Engineer (in charge).

2.

Control Room Operator.

3.

Assistant Driller/Derrickman.

4.

Service Mud Engineer.

5.

Mud Loggers.

Ensure that there is always a watcher at the side of the installation observing the boat and hoses to raise the alarm in the event of a leak. The Master/Barge Engineer may perform this task himself if necessary. •

Inform personnel before pumping starts and seek confirmation from the supply boat master when pumping actually starts.

The Service Mud Engineer should take samples to ensure that there has been no contamination on the supply boat and to ensure that the correct fluid is being pumped (i.e. base oil to the storage tank, oil base mud to the pits). The Assistant Driller/Derrickman/CRO/Mud Loggers should monitor and record quantities as required. •

Upon completion of the loading operation, the Assistant Driller/Derrickman, CRO, Mud Engineer and Supply Boat Master should tally up quantities transferred and identify/explain any discrepancies. Loading Valves and Lines should be secured and valves chained and locked as required.

Transfer Of Base Oil To Mud Pits •

Assistant Driller/Derrickman should check that required valves are open, dump valves are closed etc. before starting transfer operations.

•

CRO/Barge Engineer should dip the storage tank before and after the operation to check volumes.


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•

Assistant Driller/Derrickman should monitor the transfer and ensure that good communications are maintained during the operation. Mud Loggers may assist in monitoring quantities.

•

Upon completion of the operation, Volumes should be tallied up by Assistant Driller/Derrickman and CRO and compared for discrepancies. (It is essential to determine volume contained in the transfer system and tank “dead” volumes when carrying out comparisons.) Transfer Volumes should be recorded on both :1.

Daily Marine Log.

2.

Active Mud System Record.

3.

Pit Room Mud Tank Volumes.

OBM Management During Well Circulation •

It may be necessary to run one shale shaker with larger mesh screens at the start of OBM circulation until the mud warms up and the gels break down.

•

Ensure that Shaker House and Pump Room are manned at all times (Ref: Section 5.3.2 in DOP 202). Driller must be informed immediately and circulation rate reduced if any OBM is lost over the screens.

•

A high pressure washdown gun fed with base oil should always available to wash shaker screens which might be blinding off.

•

If losses at the shakers start to occur then the following procedure is recommended :-

•

1.

Shaker Hand advise Driller to cut back on circulating rate.

2.

Assistant Driller to go to the Shaker House (advise Mud Engineer of the problem).

3.

Wash Screens/Carry out Screen Changes as required to prevent losses.

4.

Advise Driller when it is possible to increase pump rate to optimum for hole cleaning.

Keep decks clean and clear of OBM using Mud-Vacs to minimise slippery conditions and to avoid OBM being carried to non-working areas.


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OBM Management During Tripping •

Maintain good trip records. Investigate any discrepancies thoroughly.

•

Slug pipe to ensure pipe is as dry as possible. To reduce the build-up of OBM on the setback area, it is good practice to pour one or two bucket contents of base oil down the string to clean the pipe.

•

If it is necessary to pull pipe wet, then a mud bucket must be used. Ensure that this is well drained before removing same.

•

Assistant Driller should carry out a visual inspection of the Trip Tank Recirculating system to identify/isolate any leaks.

Clean Up When Finished With OBM

5.2.2.1

•

Flush Surface Manifolds, mixing manifolds, mud transfer lines to mud pits.

•

Wash down all Shakers, gratings on top of pits etc. with high pressure gun (& detergent if necessary).

•

Allow pits to settle and separate off water. Clean up water with detergent and dump same when clean enough.

•

Transfer dirty sludge to a slug pit. This will be transferred to a boat or collection tank. Use Mud-Vacs to clean pits. If pits are still not clean, wash down again with detergent, transfer sludge and again use Mud-Vac to remove the last of the sludge.

•

Once pit is clear of OBM, wash out with sea water.

Pseudo Oil Based Mud These fluids have all the advantages and applications associated with Oil Based Muds and the same procedures outlined for the use of OBM must be followed. POBM’s have zero toxicity and are biodegradable and thus in theory can be discharged. This has been achieved by replacing the mineral oil content phase of the drilling fluid with Ester, an organic derived “oil”. POBM is an expensive mud system in terms of unit cost per barrel, however it is extremely cost effective when compared with the overall well cost of using water based mud or other mineral based muds. The cuttings can also be sent ashore for disposal or re-injected. Minimising surface losses is the key to POBM cost effectiveness and it is crucial that all practices relating to mud handling referred to in this section are adhered to. NOTE:

5.3

Due to the high wax content in POBM, the system is highly susceptible to low temperature gellation. Upon resumption of circulation after a period of the well being static all shale shakers should be fitted with coarse screens to minimise surface losses and circulation rates reduced to allow the mud to shear.

Drilling Fluid Field Tests


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It is necessary to perform certain tests to ensure that the mud is in proper condition to perform its various functions. More detailed information is available in Drilling Fluid Manuals and Textbooks. The API has recommended standard methods of testing in API 13B "Standard Field Procedure for Testing Drilling Fluids". Tests 5.3.1 and 5.3.2 will generally be carried out by the Derrickman/Shaker Hand and the results noted on the Daily Mud Weight Record (see Enclosure 1) and three results for the shift will be recorded on the IADC Report. The other tests will be carried out by the specialist Mud Engineer and will be recorded on the Contract Mud Report as per the Operators Requirements. Reserve pit volumes should also be recorded (see Enclosure 2). 5.3.1

Mud Weight This may be reported as: Ib/gal, Ib/cu.ft, psi/1000ft or s.g. This is measured using a Mud Balance. It is important that this is checked for proper calibration daily. Fresh water density = 8.33 PPG or 1.0 s.g.

5.3.2

Viscosity This is measured using the Marsh Funnel and is reported in seconds per quart. It is important that calibration is checked regularly. The calibration is carried out with water at 70ºF (plus or minus 5ºF.). This should be 26 seconds per quart (to within ½ sec each side). Supplementary information is obtained with the Fann V-G meter, particularly with regard to the gel properties of the mud. This supplies Apparent Viscosity, plastic viscosity, yield point and gel strength.

5.3.3

Filtration This is a measure of the wall-building property of the mud. This is determined using a filter press. The test determines the rate at which fluid is forced from a filter press containing the mud sample under specified conditions of time, temperature and pressure and measuring the thickness of the solid film left on the filter paper.

5.3.4

Sand Content The sand content of mud is determined using a sand-screen set. This measures sand content as a percentage by volume. It is important to monitor this closely as high sand contents will lead to abrasion in lines and mud pumps. Pump problems can be minimised by maintaining low sand contents.

5.3.5

Liquids And Solids Content Mud properties such as density, viscosity, gel strength and filtration rate depend to a considerable degree upon the solid content of the mud. Solids content is determined by evaporating a weighed portion of mud and weighing the residue. Fluid content can be found by distilling the mud, condensing and measuring the liquid. The volume of liquid; oil and/or water is measured directly as a percentage. In Salt Water Muds, it is necessary to apply a correction for the salt content as found by filtrate analysis.


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PH Concentration The pH of a drilling fluid indicates its relative acidity or alkalinity. Double distilled water is neutral, it is neither acid or alkaline. This is represented by a pH of 7. Acids are represented by PH’s 1 - less than 7, a strong acid is seen with a pH of less than 1. Alkaline solutions range from just above pH 7 to a pH of 14 for strong alkaline solutions. Two main methods are used for determining the pH of drilling fluids. One is based on the colour changes seen for different PH’s when using phydrion paper. These colours are compared with a standard colour chart to read pH. The other method uses a Glass-Electrode pH meter which gives a direct measurement of pH. The control of the drilling fluid pH is important for several reasons; minimising steel corrosion, treating chemicals will not react correctly if the pH range is wrong and their action may become inhibited.

5.3.7

Filtrate Analysis These are chemical procedures which are used on mud filtrates to the presence of contaminants, such as salt or anhydrite (Calcium Sulphate),or to assist in the control of mud properties. These tests are applied to mud make-up waters as they may contain salts which affect mud treatment. Tests can be done to estimate properties such as :Alkalinity determination:

High pH muds, Lime Content estimation controlling properties of lime muds Salt Concentration (Chloride) - significant in areas where salt can contaminate the drilling fluid. Preservative Concentration - where a preservative is being used to prevent deterioration of a treating chemical e.g. fermentation destroying starch.

Hardness Tests:

Measuring calcium and magnesium salt concentrations. A hard water will require more bentonite to make a good gel mud as drilling clays have low yields when mixed in hard water.

Resistivity:

Control of this may be desirable for better formation evaluation from electric logs. This is determined by measuring the resistance to electrical flow through a sample.



Drilling Fluids Methylene Blue

5.4

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Test: this supplies information about the nature and type of clays present in the mud. The same information is also required about the clays and shales that are being drilled, since they become part of the mud system.

Solids Control Mud solids control is one of the most important aspects of mud management. Drilled solids have adverse effects such as :-

5.4.1

•

Increased drilling fluid maintenance costs.

•

Difficulty in maintaining proper mud rheological properties.

•

Reduced Penetration rates.

•

Decreased Bit Life and increased wear on pump parts.

•

Increased frequency of differential sticking.

•

Increased circulation pressure losses.

Solids Control Equipment Mechanical removal of drilled solids is accomplished by three techniques :•

Screening.

•

Centrifugal force.

•

Combinations of 1 and 2.

It is essential to properly set up and sequence solids control equipment to achieve successful solids removal of an upstream unit will result in overloading on downstream equipment and a corresponding decrease in efficiency. Proper Sequencing of Equipment - order of flow from well. For Unweighted Muds

For Weighted Muds

(i)

Shale Shakers

(i)

Shale Shakers

(ii)

Degasser (if used)

(ii)

Degasser

(iii)

Desander

(iii)

Desander (use with caution)

(iv)

Desilter

(iv)

Centrifuge

(v)

Centrifuge

Shale Shakers


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The minimum size of screen mesh to be fitted will be determined by circulating rates, solids loading (dependent on penetration rate, screen area and mud viscosity). Allowances will have to be made when commencing circulation when muds are cold and until gels break down. Larger mesh screens may have to be carried on one shaker to allow for this. Once the mud has warmed up and become slicker then flow can be diverted to finer screens. Centrifugal Equipment These rely upon particle separation by size and specific gravity. •

Desanders/Desilters - These use hydroclones which are constructed in such a way that as the mud is fed into them, a whirling motion of the fluid is induced. Larger/heavier particles are thrown outward and tend to fall towards the tip of the cone. The fluid and lighter particles rise towards the top of the cone and are returned to the mud system.

•

Desander cones are usually 6" - 12" I.D. A common set up has enough cones to process 150% of the mudflow.

•

Desilter cones are usually 4" I.D. and again enough are fitted to process 150% of the mudflow.

•

Mud Cleaners - These are a combination unit with a desilter mounted above a fine screen shaker. Sufficient cones are used to process 100% of the mud flow. The overflow from the desilter is returned to the mud system. The underflow is processed by the screen. This separates the barite from the solids not separated by the cone.

•

Centrifuges - There are two basic types of centrifuge used to recover barite and remove viscosity producing fine solids.

These are the decanting centrifuge and the concentric cylinder centrifuge.

5.5

Corrosion Control Corrosion is a severe and costly problem in drilling. As the tubular goods are mostly iron based and drilling fluids are mainly water based then corrosion is almost inevitable. This is minimised by the use of internal plastic coatings on drill string components but it is still to be considered, particularly in wells which have greater concentrations of corrosive agents.


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Corrosive agents within the mud are :Oxygen From the atmosphere, reacts with the iron to form oxides. This is shown by pitting of the steel, can be either localised (deep pits) or general (evenly distributed shallow pits). This is treated and removed from the mud with Scavengers injected directly into the pump suction. Maintaining high pH will help control corrosion rates. Use of film forming chemicals may be considered where necessary. Carbon Dioxide From formations and the bacterial degradation of mud chemicals. This is shown by severe pitting (worm eaten appearance). This is treated by maintaining pH of 9.5 or higher using caustic soda or lime where the intrusion is not too severe. More severe cases may require treatment with film forming chemicals. Hydrogen Sulphide Formations are the primary source, but minor amounts may be produced by bacterial and thermal degradation of mud chemicals. This is shown by severe pitting, embrittlement and stress cracking. Some generalised pitting and black sulphide coating may be seen. This is treated by maintaining an alkaline mud with caustic soda/and or lime and scavenging the sulphides formed. The corrosivity of a drilling fluid may be estimated using preweighted ring coupons. These rings are sized to fit into the relief groove in the tool joint box. The rings are placed in the drill string and exposed to the fluid for a period of time. during the drilling operation. Detailed procedures and testing times will be produced if and when it is decided to carry out a corrosivity check. Safety When Working With Mud Chemicals It is essential when transporting, storing, mixing and testing Drilling Muds and Treating Chemicals that all safety precautions are observed as noted Ref: Chemical Data Sheets and Safety Manual SAF 200.

6.0

REFERENCES Chemical Data Sheets SAF 200 Safety Manual WCO 200 Well Control Manual


Drilling Fluids 7.0


ENCLOSURES Enclosure 1

Active System Mud Record (QA Documented Form 036)

Enclosure 2

Pit Room Mud Tank Volumes (QA Documented Form 037)


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Drilling Fluids

Enclosure 1

ACTIVE SYSTEM MUD RECORD



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Active System Mud Record RIG ………… TIME

WELL No .............

MUD IN WEIGHT VISCOSITY

DATE ............

ACTIVE PIT LEVEL

TOUR FROM .......... TO ...........

MUD OUT WEIGHT VISCOSITY

REMARKS Previous Tour End of Tour Pit Levels

CHEMICALS USED IN ACTIVE SYSTEM TYPE

QUANTITY

TYPE

QUANTITY

Signature of Derrickman.........................................

G:\Management Library\Forms\Offshore\QA Documented Forms\036 – Active System Mud Record.doc - Rev 1

Page 1 of 1

Drilling Fluids

Enclosure 2

PIT ROOM MUD TANK VOLUMES



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Pit Room Mud Tank Volumes RIG……….. WELL No................... DATE .................. TOUR FROM .........TO....... TIME

PIT 1

PIT 2

PIT 3

PIT 4

PREMIX

SLUG

VOLUME

VOLUME

VOLUME

VOLUME

VOLUME

VOLUME

Wt

Wt

Wt

Wt

Wt

Wt

Vis

Vis

Vis

Vis

Vis

REMARKS

Vis

CHEMICALS USED TYPE

QUANTITY

TYPE

QUANTITY

Signature of Derrickman...........................................

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DOP 205 - Rev 6

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