Modularization and Installation, Maintenance, and Repair Aspects of GASP Technology
Authors: Dick Peter , Felton J.A. 
Published: December 2007

The Goodfellow Assocs. Susbsea Processing (GASP) project addressed most ofthe major project addressed most of the major problems posed by the developmentproblems posed by the development of remote, small, marginal, or satellitefields in deep waters. It considered a number of field development scenariosand, in particular, reviewed cases for fields situated up to 30 km from aplatform- or shore-based processing facility. During the design processingfacility. During the design of the resultant modularized GASP system, it wasdetermined that an inspection, maintenance, and repair (IMR) philosophy neededto be developed. The number of field development scenarios involved, thedifferent module dimensions and weights, and the remote diverless activitiesrequired in deeper waters resulted in a separate project, Maintenance and Retrieval Equipment (MARE).

Introduction

In 1983, Goodfellow Assocs. Ltd. started a program to develop future subseaprocessing systems. The GASP project evolved processing systems. The GASPproject evolved from that program. The idea of subsea processing is not new. Indeed, in 1969, an processing is not new. Indeed, in 1969, an experimentalsubsea/seabed processing system was installed at the Zakum field offshore AbuDhabi. The range of equipment and techniques investigated during the GASPproject covered many aspects of subsea project covered many aspects of subseaproduction. In addition to primary production production. In addition toprimary production equipment (e.g., wellhead, valves, actuators, andflowlines), a range of ancillary equipment and support services (e.g., separators, electric power, instrumentation, and diving and support vessels)were also included. However, although all the components of a subsea processingsystem were in place, extensive diving was required to commission the system onthe seabed. Subsequently, it was seen that a modularized approach to systemdesign would reduce this activity considerably. Some personnel now with Goodfellow Assocs. had had extensive involvement with this early project, andduring 1983–86 the company undertook three joint industry projects coveringmarginal field studies, early production and subsea systems, and subsea systemrequirements. In 1986, Project 4, GASP, was started and was backed by eightoil-company participants and the European Community. The participants and the European Community. The GASP project was divided into three stages: Stage 1conceptual development of the subsea processing system, Stage 2-development ofa prototype system, and Stage 3-testing of the prototype system.

Modularization Approach

GASP is a stand-alone system that enables production and processing ofproduced oil production and processing of produced oil in close proximity tosatellite wells or subsea production templates, which could be 30 km or moreaway from an existing offshore structure. The system uses separators andconventional pumps. The design philosophy was to use as much known technologyas possible while allowing versatility to possible while allowing versatilityto embrace future field developments.

A typical small field development could have four producing wells and fourwater-injection wells that assist in EOR. The crude oil from the four producersmust be commingled and its flow controlled before separation. This is done witha manifold containing one choke valve per well. The crude is combined into asingle flow after the chokes. The flow is then divided into two parallelstreams of separators, each capable parallel streams of separators, eachcapable of handling about 60% of the total through-put to allow production tocontinue at a reduced rate if one separation stream fails or requiresmaintenance. If necessary, each stream may contain up to two separator vesselsto allow two stages of separation. In the first stage, as much gas as possibleis removed, leaving the remaining oil, water, and a small amount of residualgas to flow into the second-stage separator. The second-stage separator thenremoves the water and any residual gas from the oil, which will be at a lowerpressure than the first-stage gas. The high-pressure gas is passed through anejector used to drive the low-pressure gas and to commingle the two products. From here the gas will flow under its own pressure back to the mother platformfor further pressure back to the mother platform for further processing. Theoil from the second-stage processing. The oil from the second-stage separatoris routed by a single-phase booster pump, a pig launcher manifold, and finallypump, a pig launcher manifold, and finally along a pipeline either back to themother platform for further processing or, if already platform for furtherprocessing or, if already at export quality, into a nearby main exporttrunkline. Similarly, the water is boosted back to the platform for cleaningand made ready for rejection or dumping. The basic modules of the GASP systemdeveloped as the base case were (1) the production choke module; (2) the first-and production choke module; (2) the first- and second-stage separator module;(3) the gas export module, including pig launcher; (4) the oil and waterbooster pump modules; (5) the oil export module, including pig launcher; and(6) the power and control module. Electric power is supplied by a power packmodule consisting of an electrical pack module consisting of an electricaltransformer (generally 11-kV input, 3.3-kV output) and one or two electricsubmersible motors. The power pack module also contains one or two hydraulicpump and reservoir units driven by the electric motor.