ABSTRACT

This paper describes a Subsea Powered Autonomous Remote Control System (SPARCS) designed to control subsea wells without the use of electro-hydraulic umbilical between the seabed and topsides SPARCS 1s intended to provide a low cost control solution to justify subsea developments m small and marginal oilfields

Each of the main system components is described and a commercial justification is given for the system as a whole

SPARCS is highly innovative in that it has been designed to control hydrocarbon and water injection wellheads without the use of a control umbilical It relies on acoustic telemetry, with seawater as the transfer medium The system's electrical power subsea is produced by a turbine generator fitted to a water injection flowline or a thermoelectric generator fitted to a production flowline Hydraulic power for operating wellhead and downhole safety valves is produced from a subsea unit

Development is well advanced and will culminate in an 18-month offshore application trial planned to commence in 1995 on the Saltire development in the North Sea

INTRODUCTION

Offshore hydrocarbon recovery using subsea production facilities is now a mature technology and is used extensively as North Sea oil exploration moves towards marginal fields and smaller fields connected to the existing Infrastructure In order to justify these developments there is continuous pressure to reduce costs

The SPARCS system has been designed to meet these cost reduction targets SPARCS (Subsea Powered Autonomous Remote Control System) is a system designed to control subsea development wells without the use of electro-hydraulic control umbilicals back to the surface The umbilical is one of the main cost Items of a subsea control system, and SPARCS 1s targeted at providing maximum cost-reduction benefits for single well or satellite wells conventionally requiring dedicated umbilicals of lengths up to 10 km

SPARCS has two groups of components

  • A Subsea Control Unit mounted near the well and providing all the control and data-monitoring functions Depending on the type of well to be controlled, electrical power is produced by a turbine generator driven by a water injection flowline or a thermo-electric generator clamped to a production flowline The unit also contains a means of generating hydraulic power on the seabed using a closed loop-reservoir hydraulic power unit and a battery system

  • A Surface Controller comprising an operator-interface console and the acoustic telemetry system

A diagram of SPARCS is shown in Figure 1 and can be compared with the typical existing multiplexed electro-hydraulic control system using umbilicals shown In Figure 2

DESIGN PHILOSOPHY

The overall design philosophy of SPARCS has been to produce an autonomous subsea production control system that conforms to the same functional requirements, engineering standards and safety codes of practice that existing control systems satisfy Because it is an autonomous system, particular emphasis has been paid throughout the development on safe operation, any single point failure will not leave the well in an unsafe condition

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