Download Offshore Engineering for Structural Engineers...
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
