OFFSHORE ENGINEERING FOR STRUCTURAL ENGINEERS
Facilitator: Kunle Adeleke
[email protected]
March 2009
Table of Content
Introduction T Types off Offshore Off h Platforms Pl tf Fixed Platform Description Acronyms & Terminologies
1.0 INTRODUCTION •
Oil and gas are considered among the world's most important resources. The oil and gas industry plays a critical role in driving the global economy.
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Oil is not only an essential raw material to over 2,000 end products but is also used for transportation, heating, electricity and lubrication. It supplies about 50% of the world’s total energy requirements.
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About 90 countries produce oil, although a few major producers account for the bulk of world output.
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Oil and gas reserves are heavily concentrated in the Middle East, and gas in the Russian Federation. About 40% of the world’s crude oil are supplied by 12 OPEC countries (Algeria, Angola, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar Saudi Arabia, Qatar, Arabia the United Arab Emirates and Venezuela) Venezuela). They account for about two-thirds of proven reserve.
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Major non-OPEC oil producing countries are, the United States, Mexico, Denmark, Norway, the United Kingdom and Russia, China and Vietnam.
1.1 The Industry • The petroleum industry comprise upstream and downstream sectors. • Upstream involves exploration, development, and production of oil and gas. • Downstream covers transport, refining, petrochemicals, distribution, and retail.
1.2 Exploration Oil and gas exploration encompasses the processes and methods involved in locating and discovering potential sites for oil and gas drilling and extraction. This is the first-stage of oil and gas production. Many uncertainties exist during the exploration process. process Geological surveys are conducted for onshore exploration and seismic imaging for offshore exploration.
Seismic display in a visualization room
Colour display of an Oil & Gas field
1.3 Drilling & Extraction Drilling is the final stage in the exploration process. When 3D seismic has been completed, it is time to drill the well. Onshore exploration relies on fixed or mobile drillings rigs. Offshore exploration can require fixed offshore Jackup drill rigs, SemiSubmersible drill rigs and Deep Water Drill Ships. Larger production platforms may also l h have their h i own production d i d drilling illi equipment. i •
Jack-up Drill Rigs, as the name suggests, are platforms that can be jacked up above the sea using legs which can be lowered like jacks. These platforms, used in relatively low depths, depths are designed to move from place to place place, and then anchor themselves by deploying the jack-like legs.
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Semi-submersible Drill Rigs: having legs of sufficient buoyancy to cause the structure to float, but of weight sufficient to keep the structure upright. Semi-submersible rigs can b moved be d ffrom place l tto place; l and d can b be b ballasted ll t d up or d down b by altering lt i th the amountt of flooding in buoyancy tanks; they are generally anchored by cable anchors during drilling operations, though they can also be kept in place by the use of dynamic positioning. Semi-submersible can be used in depths from 600 to 6,000 feet (180 to 1,800 m).
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Drillships, a maritime vessel that has been fitted with drilling apparatus. It is most often used for exploratory drilling of new oil or gas wells in deep water but can also be used for scientific drilling. It is often built on a modified tanker hull and outfitted with a dynamic positioning system to maintain its position over the well well.
Onshore Drilling Rigs Components of a drilling rig
Onshore drilling rig, Sonora Field, West Texas
Offshore Drilling Rigs
Jackup Drilling Rig
S iS bD Semi-Sub Drilling illi Ri Rig
West Polaris Drillship
1.4 Onshore Development In onshore development, the wells are grouped together in clusters forming a gathering system. This gathering system consists of a network of connecting carbon steel pipes which sends the oil and gas to a production and processing f ilit facility. While there are oil or gas only installations, more often the wellstream will consist of a full range of hydrocarbons from gas (methane (methane, butane butane, propane etc.), condensates (medium density hydro-carbons) to crude oil. With this well flow we will also get a variety of non wanted components such as water, carbon dioxide, salts, sulfur and sand. In the production and processing facility the oil and gas is treated through chemical and heating processes. The oil and gas is then separated from water and sediments and placed in storage after which the resources can be pumped d th through h pipelines i li tto lloading di tterminals i l where h th the resources are ready d to be transported by oil tankers or transport vehicles. The water removed from the oil and gas is also treated and eventually pumped back into the reservoir.
1.5 Offshore Development In offshore development, depending on the size and water depth, different types of structures are used. Drilling wells can be conducted from either the platform or underwater. The production from the wellheads feed into the production and test manifolds from where the crude is sent into the separators. The production and extraction process can consist of fixed platforms or floating vessels. Offshore platforms contain processing equipment and facilities onboard and the resources extracted are transported by pipeline or stored so it can be loaded on tankers. Additional processing requirements are completed at onshore production facilities. p In gas production and development, production and condensation plants are required in which a liquefaction plant provides treatment, refrigeration and liquefaction followed by the storage and loading of liquefied gas. The gas is transferred to liquefied natural gas tankers (LNG's) which transports the gas to a treatment plant where the gas undergoes re-gasification from storage tanks at the plant plant.
Oil & Gas Production Process
2.0 TYPES OF OFFSHORE PLATFORMS The different development options can be broadly classified into three categories: •
fixed platforms,
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floating systems,
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subsea systems
2.1 Fixed Platforms These are the structures that physically sit on the bottom of the sea. sea Being held by the sheer weight of the structure or by piles driven into the seabed to hold them in place. Fixed platforms are economically feasible for installation in water depths up to about 1,700 feet (520 m). They include: •
Jacket-based platforms: these consist of a jacket and a deck. The jacket is tall, vertical section built from tubular steel members and is locked to the seabed by driven piles. The deck (or topside) is where crew quarters, production facilities and drill rigs p g are located.
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Compliant towers; - these are made of tubular steel members and are fixed to the bottom with piling, and supports a deck. Compliant towers are designed to sustain significant lateral deflections and forces, and are typically used in water depths ranging from 1,500 and 3,000 feet (450 and 900 m).
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Gravity base platforms; - They are enormous concrete fixed structures placed on the bottom, typically with oil storage cells in the “skirt” skirt that rests on the sea bottom. The large deck receives all parts of the process and utilities in large modules. Gravity base platforms are used in up to 1000ft of water, but the seabed has to be especially firm to ensure no creep over time.
Shallow water complex: They contain several independent platforms with different parts of the process and utilities limked with gangway bridges bridges. Individual platforms may include Wellhead platforms, Riser Platform, Processing Platform, Gas Compression Platform, Accomodation Platform and Power Generation Platform.
Ekofisk Field Center by Phillips Petroleum (ConocoPhillips)
Fixed Platform in the Gulf of Mexico
Gravity Base Platform
Living Quarters, Production & Gas Compression Modules on a Production Platform Complex Offshore Nigeria
2.2 Floating Production Systems These include TLPs, FPS’s, spars, and FPSOs. All four have to be moored in place with tendons or wire rope and chains in order to stay connected to the wells below. •
Tension leg platforms (TLPs);- these have floating hulls made of buoyant columns and pontoons. Steel pipe tendons hold the hull below their natural level of flotation flotation, keeping the tendons in tension and the hull in place eliminating most vertical movement of the structure. TLPS are used in water depths up to about 6,000 feet (2,000 m).
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Spar platforms;- consists of a single tall floating cylinder hull, supporting a fixed deck. The large cylinder, weighted at the bottom stabilises the structure in water. Eight g to 16 wire or synthetic y rope p and chain combinations moor the hull to the seabed.
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Floating production systems (FPS’s);- these consists of ship shape, TLP-like, or a semisubmersible hulls with production facilities on board board.
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Floating production, storage and offloading systems (FPSOs): These have large ship shape, made either converted tankers or new construction. They have no drilling capability. Moored to place with rope and chain. chain They process production from subsea wells and store large crude oil volumes, accumulated for later transport by shuttle tankers.
FSO
SPAR
Agbami FPSO
Some Typical Offshore Projects
ChevronTexaco Sanha Platform
BP Thunder Horse FPU
ExxonMobil Kizomba “B” TLP
TotalFina Elf Dalia FPSO Topsides
ChevronTexaco Benguela-Belize CT Project
BP Atlantis FPU Hull
ExxonMobil Sable Compression P/F
2.3 Subsea Systems These can have single or multiple wellheads on the sea floor connected directly to a host platform or to a subsea manifold. The systems include connections by flowlines and risers to fixed or floating systems t that th t could ld be b miles il away. It can b be sett iin any d depth th water. t
3.0 FIXED PLATFORM DESCRIPTION •
Most common offshore structures used for oil/gas exploration and production.
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Suitable for water depths from <50m up to about 300m
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The deck (topside) contains drilling and production equipment
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Jacket leg - the steel or concrete structure that rises from the seabed to above the water line.
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The pilings, steel cylinders that secures the platform to the seabed
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The conductors or risers,, steel pipes p p through g which the wells are drilled, completed, and produced.
3.0 ACRONYMS & TERMINOLOGIES ABS American Bureau of Shipping AFC Approved for construction AFD Approved for design AISC American Institute Of Steel Construction Annulus Space between concentric casing strings. API American Petroleum Institute API Gravity An arbitrary scale expressing the relative density of liquid petroleum products. ASME American Society of mechanical engineers engineers. Associated gas Naturally occurring reservoir gas found in association with oil, either dissolved in the oil or found as a cap or pocket of free gas above the oil. AWS American Welding Society.
Barrel A common English-unit measure of liquid volume which, in the petroleum industry, equals 42 U U.S. S liquid gallons for petroleum or natural gas liquid products measured at 60°F and equilibrium vapor pressure. BOM Bill of material Caisson Length of pipe extending vertically downwards from an installation into the sea as a means of depositing of waste waters, or of a location of a sea water pump Casing Pipe used to line and seal the well and prevent collapse off the borehole. A number of casing strings (lengths) are used in ever decreasing diameters. Casing head gas Unprocessed natural gas produced from a reservoir containing oil. It contains heavier hydrocarbon vapors and is usually produced under low pressure from a casing head on the well. Catenary mooring System consisting of multiple chains or wire ropes spreading from the buoy or tanker to the anchor points. Cathodic protection Corrosion protection system which relies on sacrificial anodes or impressed current to protect submerged steel components from corrosion by electrolytic action.
CB Control Buoy CCR Central Control Room. CGT Compliant Guyed Tower Choke A valve like device with a fixed or variable aperture specifically intended t regulate to l t the th flow fl off fluids. fl id Christmas tree An assembly of valve attached to the wellhead and used to control well production. production CO Change Order Condensate The liquid formed by the condensation of a vapor or gas; specifically, the hydrocarbon liquid separated from natural gas because of changes in temperature and pressure when the gas from the reservoir was delivered to the surface separator.
Conductor The first and the largest diameter pipe to be inserted (spudded) into the seabed when drilling a well. It keeps the hole open, provides a return passage for the drilling mud and supports the subsequent casing strings. CPT Compliant Piled Tower. CPU Caisson Production Unit. DALs Design Accident Loads. DPR Department p of Petroleum Resources Dynamic positioning Satellite monitoring system used to control the action of thruster propellers to maintain a vessel on location without deploying anchors.
EIA Environmental Impact Assessment (analysis) EPCI Engineering Procurement Construction Installation FAT Factory Acceptance Test FEED Front End Engineering and Design Flexible Riser Flexible, usually reinforced polymer pipe, for transmission of oil/gas between seabed and FPS. Flow line Pi i which Piping hi h di directs t wellll fluids fl id ffrom wellheads llh d tto manifold if ld or fifirstt process vessel. FP Full Penetration FPDSO Floating Production, Drilling, Storage and Offloading System.
FPS Floating Production System FPSO Floating, Production, Storage and Offloading System FPU Floating Production Unit GA General Arrangement Gas injection j The injection of a natural gas into a reservoir to maintain or increase the reservoir pressure or reduce the rate of decline of the reservoir pressure. Gas lift A method th d off b bringing i i crude d oilil or water t tto th the surface f b by iinjection j ti gas into the producing well bore. Gathering system The network of pipelines which carry gas from the wells to the processing plant or other separation equipment. Grout Mixture of cement and water (no sand) used to secure and seal attachment ssuch ch as piles into jacket legs legs.
HAZID Hazard identification studies HAZOP Hazard and operability studies. IDC Inter Discipline Check IFA Issued For Approval IFC Issued For Construction IFI Issued For Information IFP Issued For Preliminary Design IIF I id t and Incident d IInjury j F Free. Jacket Steel support framework used to support platform topsides
Lean gas (1)The residue gas remaining after recovery of natural gas liquids in a gas processing i plant. l t (2)Unprocessed gas containing little or no recoverable natural gas liquids. Lean oil Absorption oil as purchased or recovered by the plant, or oil from which the absorbed constituents have been removed. Light hydrocarbon The low molecular weight hydrocarbons such as methane, ethane, propane and butane. LNG (liquefied natural gas) The light hydrocarbon portion of natural gas, predominately methane, which as been liquefied LPG Liquefied petroleum gas, essentially propane and butane held in the liquid state under pressure to facilitate storage and transportation. LQ Living Quarters
LSA Life Saving Appliance Manifold An assembly of pipes, valves and fitting by which fluid from one or more sources is selectively directed to various process systems. Marine drilling g riser p pipe p extending g from the blowout p preventer on the seabed to the drilling rig on the surface, to permit the return of the drilling mud. MH Man Hour MODU Mobile Offshore Drilling Unit MTO Material Take-off Mud line The base of the jacket at the seabed Natural gas g Gaseous form of petroleum. Consisting predominately of mixtures of hydrocarbon gases. The most common component is methane. NNPC Ni i N Nigerian National i lP Petroleum l C Corporation i
PDMS Plant Design Management System PFD Process Flow Diagram Pig Spherical device inserted into a gas sub sea pipeline to sweep the line of deposits of rusts scale and condensated liquids. rusts, liquids May also be used to clean oil pipelines of wax and may be ”intelligent”, that is containing measuring and inspection equipment. Pigging A procedure for forcing a device through a pipeline for cleaning purposes, separating products, d t or inspecting i ti th the liline. Pipeline Piping used to convey fluids between platforms or between a platform and a shore facility. facility PP Partial Penetration Pressure vessel Container, normally cylindrical used to contain internal, or occasionally external pressure. Produced water F Formation ti off water t removed d from f the th oilil and d gas iin th the process off pressure vessels. l PSV Pressure Safety Valve.
PWHT Post Weld Heat Treatment Quantity assurance A sequence of planned and systematic action necessary to provide adequate confidence that a product or service will satisfy given requirements of quality. quality Quality control The operational techniques and activities that are used to ensure that a quality product or service will reproduced reproduced. Raw gas Unprocessed gas, or the inlet gas to a gas processing plant. RFQ Request For Quotation Rig g A term normally associated with drilling equipment, that is a drilling rig. Also a slang term used extensively to describe any of the structures and vessels associated with oil and gas production and exploration exploration.
Riser The vertical portion of a sub sea pipeline (including the bottom bend) arriving on or departing from a platform. RPE Registered Professional Engineer. Scour Removal of the sea bed in the vicinity of a jacket, sub sea wellhead or pipeline by tidal action. Scrubber Pressure vessel containing equipment designed to remove or scrub liquids from a gas stream. Semi-FPS Semi-Submersible floating Production System. Skid Steel framework used to contain equipment, may be transportable SID Safety In Design SOLAS Safety of Life at Sea (one of the international conventions)
Specific gravity The ratio of the mass of a given volume of substance to that of equal volume of another substance used as standard. Unless otherwise stated, air is used as standard for gases and water for liquids, with volume measured at 60°F and standard atmospheric p p pressure. SPM Single Point Mooring Sweet Gas containing essentially no objectionable sulfur compounds. Also, treated gas leaving a sweetening unit. S Sweet t gas Gas which has no more than the maximum sulfur and/or Co2 content defined by (1) the specification for the sales gas from a plant (2) the d fi iti b definition by a legal l l body b d . Also, Al ttreated t d gas leaving l i a sweetening t i unit. it TLP Tension Leg Platform TLWP Tension Leg Wellhead Platform
Topsides Upper pp p part of a fixed installation which sits on top p of the jjacket and consists of the decks, accommodation and process equipment Turret System either built into the hull or attached to the bow of a tanker. Consists of a large tube connected to a vessel via a slew ring bearing. Mooring chains are attached to the turret. The slew ring allows weathervaning. Flexible risers bring produced fluids into the turret turret. Fluid swivels transfer the fluid to the weathervaning tanker. Wellhead The assembly of fittings, fittings valves valves, and controls located at the surface and connected to the flow lines, tubing, and casing of the well so as to control the flow in the reservoir Wet gas A gas containing water, or a gas which has not been dehydrated Work over Re-entry into a completed well for modification or repair work WPS Welding Procedure Specification
