Modularisation and Installation, Maintenance, and Repair Aspects of GA-SP Technology
Authors: Appleford D.E. , Dick P. , Felton J.A. 
Published: October 2008

Introduction

In 1983, Goodfellow Associates Limited started a programme to develop future subsea processing systems, from which the GA-SP Project evolved. The idea of subsea processing is not new, indeed in 1969, an experimental subsea/seabed processing system was installed on the ZAKUM field offshore Abu Dhabi. The range of equipment and techniques investigated during the Project covered many aspects of subsea production. In addition to primary production equipment (eg, wellhead, valves, actuators, flowlines) a range of ancillary equipment and support services (eg, separators, electric power, instrumentation, diving and support vessel) were also included. However, although all the components of a subsea processing system were in place, extensive diving activity was required to commission the system on the seabed. Subsequently, it was seen that a modularised approach to system design would reduce this activity considerably. Senior personnel now with Goodfellow Associates had extensive involvement with this early project, and from 1983 to 1986 Goodfellow Associates undertook three joint industry projects 1, 2 and 3 covered Marginal Field Studies; Early Production and Subsea Systems; and Subsea System Requirements. In 1986, Project IV, GA-SP was started and was backed by eight oil company participants and the EC. The Project stages were as follows:Stage I Conceptual development of the subsea processing systemStage II Development of prototype systemStage Ill Testing of prototype system

The Approach to Modularisation

The GA-SP system is a stand alone system which enables production and processing of the produced oil in close vicinity of satellite wells or subsea production templates, which could be 30km or more away from an existing offshore structure. (Figure 1).

The system takes the approach of using separators and conventional pumps - the idea being to use as much known technology as possible whilst still allowing versatility within the design to embrace future field developments.

A typical small field development could have four producing wells and four water injection wells which assist in enhanced oil recovery. The crude oil from the four producers must first be commingled and its flow controlled prior to separation. This is done using a manifold containing one choke valve per well, the crude being combined into a single flow after the chokes. From here the flow is divided into two parallel streams of separators, each capable of handling approximately 60% of the total throughput to allow production to continue at a reduced rate if one separation stream fails, or requires maintenance. Each stream, if needed, may contain up to two separator vessels to allow two stages of separation. The first stage of separation is to remove as much gas as possible, leaving the remaining oil and water, along with a small amount of residual gas to flow into the second stage separator. The second stage separator then removes the water from the oil and any residual gas, which will be at a lower pressure than the first stage gas.