Testing of Lower Cost Remote Control System
Authors: Loth W.D. , Jacobs M. 
Published: December 2007

While fully autonomous subsea remote control is intuitively attractive, enduring needs for chemical supply and increasing requirements for both seafloor and downhole data recovery, pose formidable obstacles to application of autonomous systems. An alternative, which yields much of the cost savings of the autonomous approach is a Minimum Umbilical Remote Control System (MURCS), currently under test. The paper describes this THERMIE funded demonstration project, details of the equipment utilized, and outlines the rational behind its development.

The MURCS approach includes a remote, product driven, power supply, seawater hydraulics, and an electric downhole safety valve. The minimum umbilical consists of chemical supply and either a twisted pair or fibre optic telemetric link. The system is designed to mate with currently available electrohydraulic control systems substituting only pilot valves suitable for seawater service. Underwater testing incorporates a seawater hydraulics control system, including a gate valve actuator, pilot valve, and pump coupled to a surface power supply. The more complete land test on a live gas stream dosed with sand, includes a 15 kW power generator with its controls and suitable fluid conditioning. The well control system includes the electric downhole safety valve, seawater gate valve actuator, and a seawater stepping choke actuator. Testing will extend through 1998. Savings achieved with this robust technology include reduced surface facilities, substantially lower cost umbilical, and the not inconsequential cost of the hydraulic control fluid inventory required in current systems. System components can also be utilized separately. The subsea power supply could be used to power local, closed loop, controls or the seawater hydraulics could rely on surface power or pressurized injection water. Savings with these systems, also illustrated in the paper, will remain significant albeit less than with the complete MURCS approach.

Introduction

The concept being pursued by MURCS is hardly novel; it is the constituent parts which distinguish the system from its predecessors.

Umbilicals have driven many significant control system developments. Elimination of hydraulic conduits is the usual approach.

In earlier days, closed loop hydraulic systems were the favoured route. The umbilical provides electrical power for a local hydraulic pump and telemetry capability using one or more twisted pairs. By the early 1970s, these systems were fully functional; the only major problem was the need to periodically replenish hydraulic fluid lost through leakage. Sometimes, periodic turned out to be uncomfortably frequent.

The more fashionable contemporary approach, for eliminating hydraulic conduits, is all electric systems. These, at least currently, seem best suited for application in conjunction with subsea (electric) pumping where the power consumed by control functions is minuscule compared to pumping demands. In most circumstances some chemicals are required for fluid conditioning. While chemicals may be supplied through cores of a composite umbilical, they are as readily supplied through a small diameter, separate, service line.

MURCS' approach to reduce umbilical cost incorporates a number of independently developed technologies.

System and Component Descriptions

The MURCS configuration being tested is shown in Figure 1. The system can be divided into power supply and wellhead control subsystems.

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