The offshore industry presents, becomes the primary in advancement of civilisation. Oil and gas are indispensable assets in universe trade. Impact of that, there are many offshore construction worldwide. AnA offshore construction, referred to anA oil and gas platformA where it is a big construction with installations to bore Wellss and infusion and processA oilA andA natural gasA and export the merchandises to shore.
There are several type of platform depends on the fortunes, likes fixed to the ocean floor, compliant construction and floating construction. RemoteA subseaA Wellss may besides be connected to a platform by flow lines andA umbilicalA connexions. Subsea production systems can run into complexness ; from a individual well with a flow line linked to aA fixed platform, A FPSOA or an inshore installing. Otherwise it can be from several Wellss on a templet or clustered around a manifold and reassigning to a fixed or drifting installation, or straight to an onshore installing
Figure 1: Deepwater Systema Types ( Chakrabarti, 2005 )
Subsea production systems can be used to develop reservoirs, or parts of reservoirs, which require boring of the Wellss from more than one location. Deep H2O conditions, or even extremist deep H2O conditions, can used a subsea production system, since traditional surface installations such as on a steel-piled jacket, might be either technically impracticable or wasteful due to the H2O deepness.
The addition of natural gas in the energy matrix all over the universe has posed a strong demand on seaward geographic expedition and production. British Petroleum Company ‘s mentality for the hereafter shows ultimate offshore militias to be 571 billion barrels with onshore militias to make 1038 billion barrel ( Bleakley, 1998 ) .
Under H2O oil field installations are by and large referred to utilizing aA subseaA prefix, such asA subsea good, A subsea field, A subsea undertaking, andA subsea development. Subsea oil field developments are normally disconnected intoA Shallow-waterA andA DeepwaterA classs to separate between the different installations and attacks that are needed.
The term shallow H2O is used for shallow H2O deepnesss where underside founded installations like doodly-squat up boring rigs and fixed offshore construction can be used, and where impregnation diving is executable. While deepwaterA is a term frequently used to mention to offshore undertakings located in H2O deepnesss greater than around 600 pess, whereA drifting boring vesselA andA drifting oil platformA are used, and remote-controlled submerged vehicles are required as manned diving is non practical.
The first subsea well was in one of theA Great Lakes in theA USAA and was in merely a few pess of H2O and Shell wasA completed its first subsea good in theA Gulf of Mexico in 1961 ( Bleakley, 1998 )
In the Gulf of Mexico, Marathon began bring forthing at Droshky in 3,000 foot ( 914 m ) of H2O in Green Canyon block 244, 160 stat mis ( 257 kilometer ) sou’-east of New Orleans. Droshky, excessively, is tied back to an bing platform ; Bullwinkle takes the double 18-mi-long ( 29-km-long ) flow lines from Droshky. Marathon says the initial development phase is expected to bring forth 50,000 boe/d at its extremum. ( Kliewer, et al. , 2010 )
Meanwhile Petrobras is non left out. The FPSOA Cidade de SantosA in Uruguay is expected to make 25,000 b/d of oil from three Wellss, with a 4th scheduled for pullback before twelvemonth terminal to convey production to 35,000 b/d. Petrobras says the development program for Uruguay field will dwell of four horizontal oil Wellss and five gas Wellss straight connected to the FPSO. ( Kliewer, et al. , 2010 )
The development of subsea oil and gas Fieldss requires particular equipment. The equipment must be dependable plenty to safe guard the environment, and do the development of the subsea hydrocarbons economically executable. The deployment of such equipment requires specialized and expensive vass, which need to be equipped with diving equipment for comparatively H2O deepness environment work.
Pipes are the employed mechanical constituents to convey fluids. Subsea pipes are varies in sizes, typically 2 to 10 inches diameter, depend on the figure of good and the force per unit area ( Kliewer, et al. , 2010 ) . The pipes can be classified as stiff and flexible. Flexible pipes consist several beds with polymeric and metal constituents and flexing rigidness much smaller than that for stiff steel pipes.
Figure 2: Rigid and Flexible Pipes
In subsea system, pipes are map as for flow-lines. Those it subjected to the inactive burden since rested on ocean floor ( Bai, et al. , 2005 ) .
Wet Xmas Trees
The first Petrobras wet X-mas Tree was installed during April 1979 over good 1-RJS-38 in the Compos Basin Bonito Field ( Trotman, et al. , 1987 ) . In general, the maps of subsea tree vary on the nature of system. It is the equipment that installed at the wellspring to vouch security barriers in instance flow break is necessary, which assures reservoir natural force per unit area obstruction. It comprises fundamentally a set of valves, hydraulicly operated through spring return to guarantee shutting in instance of hydraulic system depressurization ( Estefen, et al. , 2005 ) . Trees can be fitted with subsea choking coils to actively modulate flow and valve system control and injection of wax chemical either downhole or into flow-lines ( Trotman, et al. , 1987 ) .
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Figure 3: Wet X-mas Tree
Subsea manifold is a set of tubings, valves and supervising instruments assembled on a metal construction, complecting the drainage/flow of several Wellss to the production unit, therefore cut downing the figure of lines that would be necessary ( Estefen, et al. , 2005 ) . The thought behind of utilizing subsea manifold is to cut down the figure of riser from the seafloor up ( Trotman, et al. , 1987 ) .
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Figure 4: Subsea Manifolds
Manifolds is the unit that as the bosom of the full system. It is made up of all necessary piping to transport out the submerged production system. It is a rectangular shaped with good rounded corners to let usage of pump-down tools.
The manifold is fail-safe. If hydraulic power is lost, or if any unnatural conditions exist, all valves near and the system are left in a safe status.
Typically subsea grapevines consist of pipes and riser. In order to link each other, riser has been use. The jumper is tied with the riser and grapevine with connection and Pipeline End Termination ( PLET ) . PLET map as support to grapevine connection and valve. At the subsea terminal, grapevine is connected to manifolds or a good through a jumper which is installed between PLET and manifold / trees by connections ( Gou, et al. , 2005 ) .
Figure 5: Schematic of typical subsea grapevine system
Figure 6: jumper diagram
Umbilical overseas telegrams are employed to command the subsea equipments remotely. They are able to reassign hydraulic force per unit area and electrical power to run submersed equipments and valves every bit good as to recover informations through electrical and/or optical fibre overseas telegrams. Umbilical can besides be used associated with extra hosieries for good chemical injection. An illustration of umbilical is shown in Figure 6.
Figure 7: Umbilical Cable
Pipe Line end Manifold – PLEM
Figure 8: Pipe Line End Manifold
The PLEM is a aggregator / distributer equipment, which is characterized by the entrance or outgoing of more than two pipes. When used in the agreement, it allows pipe sharing without operational flexibleness.
Pipe Line End Termination – PLET
The PLET makes it possible to link, without frogmans, a stiff pipe and equipment to another pipe. It features a rim connexion to be interconnected to the appendage of the stiff pipe, a obstruction valve operated by Remotely Operate Vehicle ( ROV ) to let pipe hydrostatic trial, a HUB/MCV for future connexion to flexible riser or jumper.
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Figure 8: Pipe Line End Termination
SUBSEA PROCESSING TECHNOLOGIES
Subsea developments are suited for widespread reservoir constructions. They provide a grade of vas and field enlargement flexibleness with simplified riser interfaces, but at the disbursal of high boring and workover costs.
There are three common scenarios in oil and gas industries that used subsea system in for boring system. This systems were attached either to semi-submersible construction, jacket construction or direct to subsea. However for simple apprehension, subsea production usually will associate to drifting construction, such TLP, Guyed Tower, and semisubmersible.
Example of Semi-Submersible Platform Arrangement in Brazil
( Wellss H2O deepness of 500 metres )
Model of Jacket Platform Arrangement
( H2O deepnesss decreased from 500 to 180 metres and 20km off from the Wellss )
Ormen Lange layout
Subsea processing consists of scope engineerings to let production from offshore Wellss without necessitating surface production installations. It consists of handling produced fluids upstream of surface installations on or below the ocean floor, including seabed and downhole oil/gas/water separation, downhole and seabed multi-phase pumping, gas compaction, and flow confidence. The most of import benefits from utilizing these engineerings include production boosting, improved oil and gas recovery, increased Net Present Value ( NPV ) , reduced surface production installation costs, and the lower likeliness of gas hydrate formation in flowlines.
However there are Numberss of issue that have kept subsea hiking and treating from being used more widely. The most of import issue is the dependability of subsea units. They must be able to run for long periods of clip without any perturbation. In add-on, the effects from a subsea processing system failure are more severely than those from a topside unit because when a unit of equipment fails, an interfere vas or a boring rig have to be deployed to mend or serve the unit ( Chakrabarti, 2005 ) . This downtime will take the rate of measure production and increased costs from procuring an intercession vas or boring rig.
The two engineerings in subsea processing are seabed separation and seabed hiking. The latter engineering includes seabed multi-phase supporter pumps and seabed gas compaction. In this subject subsea production system, engineerings of seabed separation will be discussed farther on their procedure, and application around the universe.
One of the engineerings in subsea processing is seabed separation. Apparently with the name, seabed separation is operation that involves of separate the oil, gas, and H2O straight at the seabed alternatively on topside installation. This development of subsea separation engineerings allow companies to treat seaward production without the sea degree production installations.
This engineering is used in mature Fieldss where H2O production progressively exceeds oil production and where it becomes economically unviable for operators to go on with the recovery of the field ‘s militias. The engineering can be used besides in green Fieldss that have high gas to oil ratios and which face the hazard of blocked grapevines because of hydrate formation.
For oil and H2O separation in mature Fieldss, cardinal factors include the degree of the field ‘s H2O production and the being of heavy oil. Meanwhile for liquids and gas separation in green Fieldss, high gas volume fraction, increased distance from the host, and low reservoir force per unit area and temperature are considered as of import parametric quantities because the conveyance of moisture gas over 10 of kilometres can take to hydrate formation and, therefore, pipe obstruction.
As mentioned at above, subsea separation systems are designed to divide bulk H2O from production watercourse near to subsea trees on the seafloor. Basic constituents of that system include centrifuge, pump to re-inject H2O, and H2O injection good. Others extra constituents include instrumentality, equipment associated with commanding the pump and centrifuge, power transmittal and chemical injection.
Figure 9: Subsea processing conventional ( hypertext transfer protocol: //www.bp.com/liveassets/bp_internet/globalbp/STAGING )
The separation of oil is basically a inactive procedure based on cut downing the force per unit area of the liquid. In centrifuge constituents, oil will go forth the wellspring at a force per unit area typically between 14 and 20 MPa. First phase in a separation unit will cut down the force per unit area of oil to 1 MPa. At this force per unit area, most of gas will be trapped in the oil released. Time taken depend on midst of the oil is ; those heating the oil will frequently rush the release of the gas.
Oil is sent by grapevine to the surface for the pilot works, nevertheless little sum volumes of gas are recombined to subsea with oil for transit to the host platform.
As H2O flows from the base of centrifuge, the sand which has settled in the vas is added to the flow. Sand will take by uninterrupted water-driven ‘swirling ‘ flow form. The H2O and sand together entered cyclonal desander for separation. The majority of the produced H2O from desander is deoiled in a cyclonal deoiler to bring forth comparatively clean H2O for reinjection into the reservoir utilizing a variable velocity thrust pump. The greasy H2O is taken from the deoiler through an eductor to fall in the chief flowline to the surface.
Normally, the export oil will incorporate between 2 % and 10 % H2O, while the reinjection H2O will be cleaned to 50-100 parts per million ( ppm ) of oil and might contained 2-10ppm sand.
APPLICATIONS SEABED SEPARATION AROUND WORLD
The first seabed separation unit was installed in Statoil ‘s Troll Olje field in 2000, while Tordis and Statoil field, being the 2nd field in the universe runing a subsea separation unit since October 2007. The driver behind these installings is Statoil Hydro ‘s improved oil recovery ( IOR ) scheme.
Unlike the Troll subsea separation undertaking, the new Tordis station is perfectly cardinal to the commercial viability of the whole field. This is because its increasing H2O out flow was curtailing production because grapevines and surface installations do non hold the capacity to transport and manage the excess H2O being produced in increasing sums by the well watercourse.
Meanwhile, Shell late installed seabed separation units in two of its green field undertakings, BC-10 in Brazil and Great White in the US Gulf of Mexico. FMC supplied six subsea separation faculties for these undertakings. At the Perdido Host Regional Development production from the first three Fieldss ( Great White, Tobago, and Silvertip ) will tieback to a cardinal separation and hiking bunch straight beneath the Perdido Host spar. The Fieldss ‘ key features are their low reservoir force per unit area, temperature, and great H2O deepness, each of which adds to hydrate possible.
Other upcoming seabed processing undertakings include gas and liquids separation at Total ‘s Pazflor field away Angola, and oil and H2O separation at Petrobras ‘ Marlim field in Brazil, Statoil ‘s Fram East undertaking in Norway, and BP ‘s Foinaven field in the UK. The Pazflor undertaking includes three seabed separation units by FMC to be installed in 2011 and expected to cut down significantly the hazard of hydrate formation. FMC besides will provide Petrobras with a seabed separation unit in 2011 for its Marlim field.
Figure 10: History Subsea Processing ( Bleakley, 1998 )
Meanwhile, Infield Systems views the mature NWECS part as a good chance for subsea processing engineering. Statoil ‘s extended exposure to Norse Waterss is an of import factor for the execution and future cogent evidence of the viability of this engineering. That operator has made a strategic determination to increase oil recovery rates from its Fieldss, and subsea processing will be the primary tool to accomplish this end.
Advantage OF SUBSEA SEPARATION
In an ideal universe, the separation procedure would take topographic point at the underside of good or in the reservoir itself. This construct of subsea separation, purposes to make on ocean floor work which separate oil from the gas and take contaminations. Therefore it will take the demand of carry out the processing on platforms. Subsea separation could be ultimate remote-controlled procedure operation. Subsea production has become an economic manner of retrieving hydrocarbons from offshore reservoir, particularly those located at deepwater.
A most attractive benefit by this engineering, which significantly more oil, could be shipped through the platform. Hydrocarbon production could non merely addition but would make its tableland degree faster and remain at that place for longer.
If adequate H2O remotion, hydrate formation could non be happening. Subsea separation system can cut down H2O flow in subsea flowline. The advantage for using subsea separation systems is non merely hydrate control, but besides increasing recovery of militias and speed uping recovery by doing the produced fluid watercourse igniter and easier to raise ( Sasanow, 1989 ) .
Subsea separation is peculiarly attractive at really great deepnesss, where it can be portion of an anti-hydrate policy. If separation public presentations is sufficient and residuary H2O content in oil is limited to a low H2O cut, anti hydrate intervention is no longer required or is limited to an injection of low dose of additives ( Falcimaigne, et al. , 2008 ) .
A subsea oil and gas production system ( SPS ) includes most of the chief elements found in a conventional platform production system, but is alone when it comes to remoteness in installing, service and operation. The figure of bing and proposed subsea hiking and treating undertakings has increased over the last few old ages. The bulk of these units were awarded prior to the recent diminution in seaward activity caused by the planetary economic downswing, force per unit areas on the supply concatenation, and oil monetary value volatility. Therefore, as a consequence of the timing of the contracts, several undertakings have gone in front despite these conditions. Most operators involved in these engineerings are either partially nationalized companies such as Petrobras and Statoil, or oil big leagues such as Shell and Total.
Subsea systems are less expensive to put in and can be brought on watercourse faster. They offer flexibleness in the location and size of the host installation and can make into H2O deepnesss where conventional development of all but the largest Fieldss would be prohibitively expensive. The drawback is that if something goes incorrect with a subsea good, intercession can be dearly-won. Although several of these oil companies aim for extra cost nest eggs in the short term, we believe there will be a continued attempt to force these techniques to better oil and gas recovery, encouragement production, cut down the platform ‘s operating cost, and cut down the likeliness of gas hydrate formation in the grapevines.
Another key concern in deepwater, long step-out applications is communication velocity and response clip. As demands for downhole informations addition in complexness, the modest communicating velocities of current manifold electro-hydraulic MUX/EH systems are challenged. Use of the all-electric control system virtually eliminates this job as communicating and power transmittal are accomplished via high-velocity coaxal overseas telegrams.
Subsea processing and boosting engineerings are a long-run aim for oil companies that face short-run fluctuations in R & A ; D investing. If these engineerings become proved victors that increase NPV they may go the preferable development solution.
The success of approaching undertakings is critical to the length of service of the deepwater oil and gas industry. The competition between makers for different engineerings, such as the helico-axial and the seabed ESP, is expected to increase. The subsea boosting and processing market is sing its first “ experimental ” phase after which ISL anticipate that these engineerings will be used more widely.