An All-Electric System For Subsea Well Control
Authors: Jernström T.L. , Sangesland Sigbjörn , Hägglin Anders 
Published: October 2008

For subsea well control, an all-electric control system is expected to be simpler and less expensive compared to a conventional electro hydraulic control system. This system is thought to be a suitable concept for control of subsea installations and may solve some of the problems concerning future field developments.

All-electric control would be favourable to use when developing marginal fields at great distances from a processing facility and it would also provide solutions to problems associated with high pressure and high temperature wells. Further. it gives a higher degree of flexibility when expanding an existing system and when introducing new equipment. The removal of the hydraulic system may also eliminate some environmental, technical and economical problems concerning the hydraulic fluids.

This paper presents an ongoing research study of an all-electric system for subsea well control. The approaching working process is briefly described. The advantages and overall system effects on the introduction of an all-electric subsea control system are investigated and discussed in a review of potential areas of interest. Further. the technical feasibility of certain key elements are discussed. Finally. some brief economical considerations have been made.

INTRODUCTION

At the Norwegian Institute of Technology, a study is performed with the objective to identify and investigate technical and economical incentives to employ electrical valve actuators and an all-electric subsea control system.

Background

The offshore oil and gas industry has a continuing need for field developments to be cost-effective. The general view of any offshore oil or gas field involves a production platform. However, nowadays the subsea development of a prospect will be one of the scenarios reviewed. During the past eight years, 24 subsea completions have been installed in the Norwegian sector of the North Sea. In the future, subsea technology will probably be used more commonly around the world and will increase its part in production of offshore hydrocarbons. It is expected that approximately 200 wells are going to be completed subsea in the North Sea between 1992 -2000.

Subsea technology offers an acceptable solution to many of the problems involved with tie-backs to existing platforms or stand alone developments. However, to meet the request of offshore field development in the future, key areas of technology will need to be advanced. One of these areas is the remote control of subsea installations.

Industrial approach

There are different control systems for subsea completions, however, all of them are in one way or another depending on hydraulic pressure for actuating valves. This hydraulic dependancy sets limits to the usability of subsea solutions due to cost and technical feasibility.

In the North sea, a significant parameter is the distance of a satellite field from an existing platform. A target would be to increase the distance between satellites and existing facilities. This is a problem if the control system depends on hydraulic fluids, due to high costs for a control umbilical with hydraulic lines.

High pressure / high temperature wells reduce the possibility of using a control system dependent on hydraulic pressure due to problems with degrading control fluid at high temperature and equipment failure at high pressure.