Development Of Control Systems For Subsea Applications
Authors: MacLennan M.A. , Huskey W.L. 
Published: December 2007

Introduction

The objective of this work was to develop a highly reliable control system for use in subsea applications throughout the offshore industry. The work involved developing subsea control equipment that is insensitive to water depth, and can be adapted to several types of installations. An extensive program was undertaken to qualify electrical and hydraulic components for service in a pressure-balanced environment through a study of failure rates and actual testing. A parallel effort involved the development of inductive couplers and subsea hydraulic power generating equipment to transmit both electrical and hydraulic power throughout the system. When these problems were solved, work followed which would transform the resulting techniques into fully integrated control systems.

Equipment has been designed for both wet or dry use, diverless or diver-assisted applications, and utilizing either surface or subsea generated hydraulic supply systems. The system was to be designed to function by implementing the means for decision-making at the surface or closed loop action recognized and activated through sensing devices incorporated into the subsea equipment.

Requirements

In response to requirements established by the foresightedness of the oil industry, a substantially great amount of development was undertaken to assist in exploiting petroleum bearing reservoirs that will be discovered beyond the existing limits of conventional production practices. The requirements were to provide a control system for application on oil and gas fields found in very deep water that may be up to twenty miles from a surface base of operations. Inherent in the concept was that operations would of necessity be beyond the capability of divers and that the control system must function as an integral part of an overall facility located subsea. The primary conditions that the control system had to meet were twofold. They were:The control system had to function in the subsea environment being subjected to the effects of corrosion and hydrostatic pressure.That maintenance and servicing were major factors in contributing to profit from the venture and the ultimate design must give due consideration to minimizing loss of production due to equipment failures.

To fulfill the requirements, it was necessary to establish specific design objectives for the system. In this manner, guidelines could be established which would allow proven, effective existing concepts and techniques to be utilized. Also, the guidelines would clearly define any necessary new development effort.

Design Objectives

The overall design effort was to monitor and control subsea production operations remotely. This would allow potential sources for the loss of production to be detected and for remedial action to be taken based on an analysis of pertinent information about the subsea facility. It was established that no action, either of control or of data acquisition nature, would be performed subsea that could normally be accomplished at the surface.

The need for a thorough and effective communications means was recognized primarily because speed in execution over a relatively long distance was necessary as was the transmission of pressure, temperature and other dynamic data.