The aim of the GA-SP Project is to develop and test full scale, a subsea processing system that will facilitate economic development of small hydrocarbon reservoirs. The system will include well stream commingling, multiphase separation and pumping, and will be engineered to be suitable for a wide range of reservoir fluid properties, shallow or deep water application, with control from the surface from either a low cost in-field floating platform or form an existing remote fixed installation.
Innovative aspects include:
a) Subsea closed loop modulating control of process parameters
b) Hybrid diverless maintenance philosophy with vertical retrieval of insert components or complete modules
c) Single datum alignment of multi-port interconnections.
d) High and low pressure gas commingling in an ejector.
e) Variable speed export pump, turbine driven using ambient sea water as a power transmission fluid.
f) Nucleonic, capacitance and differential pressure instruments for level sensing.
The west tests successfully duplicated all of the opreational functions demonstrated in the dry with only two minor instrument failures. The cost analysis of the field scenario indicated a capital cost of about 100 million UKL for a 30,000 b/d facility exporting over 30 km. The major installed cost elements in this total were :
UKL million
Trunk Pipelines, Power cable, Umbilical 39
Drilling and Well Completion 28
GA-SP Facility and Infield Lines 25
The GAP-SP Project, which is also being supported by a number of oil companies was executed in stages. The First Stage, Front End Engineering and Preliminary Design, was concerned with outline definition of field scenario concepts and identification of major areas of novelty. The Second Stage, Detailed Design and Engineering, was concerned with development of a full scale prototype system which incorporated all of the key areas of novelty required to demonstrate the technical feasibility of the concept. The major tasks of this stage of work will include :
i) Development of Process Flow Diagrams, General Arrangement Drawings and Piping and Instrument Diagrams.
ii) Building of Scales Models to show module details and interfaces.
iii) Preparation of functional specifications for all equipment, systems, fabrication and assembly requirements.
iv) Detailed engineering including hdyraulic, mechanical and structural calculations, and preparation of drawings and schedules.
V) Specificationof onshore tests facility requirements including a conditioning plant to provide a flow simulated crude oil at 15,000 b/d and 35 bar.
VI) Development of a computer simulation programme, to be used as a basis for predicting process/control response of the prototype, and subsequently, after correlation with tests results, design of commercial systems.
The main components of the prototype system include :
a) Dummy Production Choke Module (PCM), with a single bay Secondary Distribution Module (SDM) incorporating the prototype Valved Multiported Connector (VCM).
b) Separator Module, for two stages three phase separation, including four types of level detector from three manufacturers, and four sets of modulating control valves with hydraulic actuators from two manufacturing groups.
c) Ejector skid unit, with two alternate ejectors from gas commingling; flow, pressure and temperature sensors, and (manual) recycle capabilities to the second stage separator and/or booster pump suction.
d) Power system, comprising 3.3 kV transformer, switchgear and cable wih a sea water charge pump driven by 500 H.P. 3.3 kV synchronous motor. The high pressure water drives a turbine, coupled to the oil export booster pump. A modulating control valve bypasses water to control speed of the turbine/booster pump in response to separator level control.
e) Control and data monitoring system, comprising a topsides process control computer, a topsides data logging computer and printer a topsides hydraulic power unit, a subsea pod for hydraulic fluid distribution and data transmission together with a variety of transducers cables, connectors and junction boxes.
The third stage of the GA-SP project included procurement of the prototype facility, factory acceptance testing of the main components, its installation in a dry dock, commissioning and operation using circulated wellhead fluid.