Artificial Lift

www.EPmag.com July 2010 | E&P

Two landmark projects have laid thegroundwork for subsea productionsystems of the future.

AUTHORSBen Gould and Carla Loaiza,

Baker Hughes

As subsea development waterdepths and step-out lengthsincrease, operators require

more technologically advanced andcost-effective methods to producereserves over the life of deepwaterfields. The objective, of course, is tomaximize production and minimizecosts, and ultimately to expand theeconomic development limits of sub-sea technology.

The challengeIn January 2007, Shellawarded the contract for twomajor deepwater seabed pro-duction boosting systems forsubsea projects – Perdido inthe Gulf of Mexico (GoM)and BC-10 offshore Brazil –to Baker Hughes. ThePerdido system marks thefirst project using electricalsubmersible pumping (ESP)systems in seabed verticalbooster stations in the GoM.

The vertical booster sta-tions require installation ofa large 36-in. conductorpipe on the seafloor bydrilling or suction pile, ifthe seafloor is muddy. TheESP system is encased in apressure vessel with a con-nection system on top. Thesystem is lowered into the“dummy well” by a light con-struction vessel or rig. Thebooster station can belocated at any point between

the well and host facility. If more thanone field is connected to the host pro-duction platform, the booster stationmay be closer to the platform and canboost production from several fields.

In developments where several wellsare in one seabed location, the boosterstation may be needed closer to thewells. The vertical configuration ofthese installations makes gas separa-tion easier, and the pump encapsula-tion in the pressure vessel onshoredecreases installation costs. While sev-eral wells can be produced throughone vertical booster station, this setupeliminates the ability to optimize flowfrom each well. The same pressureboost is applied to each well, whichlimits the system by the lowest-produc-ing well.

The solutionBaker Hughes’ production solutionswere chosen to boost fluids from deep-water subsea fields. The seabedbooster systems minimize design com-plexity and offer higher efficiency andpressure boost capacity than alterna-tive artificial lift methods. Flow ratesup to 150,000 b/d and boost pressuresin excess of 5,000 psi are achievable.High gas fractions also can be accom-modated with a suite of multiphasepump designs.

In May 2010, Baker Hughes installedCentrilift XP enhanced run-life ESPsystems in two vertical subsea boostingstations at Shell’s Perdido field in theGoM. The setting in 8,000 ft (2,438 m)of water is a world-record water depthfor ESP installation. The Perdido sys-

tem is unique in that it hasdirect vertical access forinstallation and retrieval ofthe ESP systems.

The six systems installedin vertical subsea boostingstations at Shell’s Parque dasConchas (BC-10) field in theCampos Basin offshoreBrazil are located approxi-mately five miles (8 km)from the floating produc-tion, storage, and offloading(FPSO) facility in 5,250 to6,250 ft (1,600 to 1,905 m)of water and are designed toboost up to 100,000 b/d offluid, which is the maximumcapacity of the FPSO. Thesystems installed on BC-10do not allow direct verticalaccess and will require a rigor a light intervention vesselfor retrieval.

The Perdido verticalbooster stations handle pro-duction from three subseasatellite fields (Great White,

Seabed production boosting systems push the limits

Caisson cross-section from Argonauta B-West, part of the BC-10 field, shows gas re-blending ports just below the ESP. (Imagecourtesy of Shell)

As seen in theJuly 2010

issue of

Artificial Lift

Copyright, Hart Energy Publishing, 1616 S. Voss, Ste. 1000, Houston, TX 77057 USA (713)260-6400, Fax (713) 840-8585

Silvertip, and Tobago) tied back to thespar host facility. This is the deepestspar production facility in the world,moored in approximately 8,000 ft ofwater. The booster stations are directlybeneath the spar and are connected tothe platform via top tensioned risers.

Pushing the ESP envelopeCentrilift standard ESP systems havehigher pressure boost capabilities thanmost traditional surface systems. ESPsystems, by design, are intended to beimmersed in fluid, whether it is in thewell or on the seabed. ESP motors arepressure balanced with the environ-ment, whether that is downhole pres-sure or water pressure, in subseaapplications. Basically, ESP systems aredesigned for the subsea environment,unlike traditional surface pumps thatmust be re-engineered to overcomepressure and penetration issues. Amajor issue for any field developmentis economics, and ESP seabed boostersystems offer several advantages overother alternatives:

• Seabed ESP systems can bedeployed with vessels of opportu-nity instead of via semisub-mersible rigs, which reduces both the overall cost of installa-

tion and intervention anddeferred production resultingfrom a waiting period for a rig;

• Seabed ESP systems can be config-ured to provide a backup systemto maximize run-life and mini-mize deferred production. Someseabed ESP systems use existinginfrastructure to house the sys-tems, which also reduces overalldevelopment costs; and

• Seabed ESP booster systems arenot as space-constricted as in-wellsystems. Production from severalwells can be boosted with onlyone seabed ESP booster system.

Centrilift XP production systemsextend the capabilities of ESP systemtechnology to increase provenreserves. Historically, harsh fluid con-ditions, including high temperatures,CO2 levels, extreme abrasives, free gascontent, and hydrogen sulfide levelslimited the application range for ESPsystems. The Centrilift Performanceseries pump designs maximize vaneopenings, optimize flow paths, andinclude patented particle swirl sup-pression technology as the first line of defense against abrasive downholeenvironments. The extra-wide vaneopenings boost performance in the

presence of gas, sand, viscosity, andscale.

The technology advancements builtinto the Centrilift XP systems alsoimprove reliability in difficult opera-tional challenges, such as hard startsand uncertain or changing downholeconditions. These tasks are achievablebecause the design uses carbide bear-ings, high torsion rated shafts, and aspecial motor insulation process.Nearly all of the features have beenupgraded, such as mechanical seals,motor oil, elastomers, and couplings.The pumping systems at Perdido andBC-10 consist of two pumps that pro-duce 700 and 1,000 gal/m at theirbest efficient points, and a tandemmotor capable of generating 1,600 hp.

Centrilift Xtreme performancemotors offer high-horsepower for tech-nically challenging applications wheredownhole conditions and high interven-tion costs dictate robust, long-lastingsolutions. These motors have been glob-ally field-proven to increase ESP systemrun life in harsh well applications, allow-ing operators to increase production,reduce operating expenses, anddecrease HSE incidents at the well site.

Baker Hughes project managementteams consulted with Shell engineersregarding Perdido and BC-10 systemdetails at all stages of production anddelivery.

Throughout the process, from proj-ect award until installation and com-missioning, Baker Hughes and Shellengineering staffs collaborated toensure that the delivered project metexpectations. After the units wereinstalled, the companies workedtogether to ensure continued successby the use of monitoring and automa-tion systems, both on the host vesselsand at the Shell onshore offices. Thisteamwork will continue through thelife of the project, as both Shell andBaker Hughes continue to apply oper-ational learnings to the equipment asthe field matures.

Baker Hughes installed ESPsin caisson on the seabed toboost several production wellsin commingle with a singleunit. (Image courtesy of BakerHughes)