Application of the All-Electric Subsea Production System
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 18819, "First Application of the All-Electric Subsea Production System - Implementation of a New Technology," by Laurent Bouquier and Jean Pierre Signoret, Total, and Robert Lopez, Cameron International, prepared for the 2007 Offshore Technology Conference, Houston, 30 April-3 May.

Improvements have been made in equipment reliability, system availability, operational functionality, and environmental performance of all-electric subsea production systems (SPSs). This paper describes the process, decision criteria, and motivation that led to selecting the all-electric SPS for this North Sea application and outlines the objectives to implement the technology.

Introduction

Over the past decade, substantial gains have been realized in reliability and functionality of electrohydraulic multiplexed (EHM) control systems for subsea production. These systems use hydraulic-control technology dating back to the early days of subsea systems. The evolution of control-system technology has progressed from direct hydraulic to piloted and sequenced systems to provide improved response time and enable long-distance tiebacks. Today, most subsea developments use EHM control, which is a subsea computer/communication system of hydraulic directional-control valves. These electrically actuated valves allow stored pressure within subsea accumulators to be routed to individual hydraulic lines and onward to actuated gate valves and chokes on subsea production equipment.

Generally, industry recognizes persistent weaknesses that are related to susceptibility of fluid cleanliness, materials compatibility, hydrostatic effects in deeper water, and limitations for long-distance tiebacks. Many reliability problems are attributable to hydraulic-component failure. Reliability issues occur during installation and during operations associated with high-pressure/high-fluid-volume hydraulic systems. Reliability studies initiated significant technology-development investigations to explore the potential of all-electric subsea controls.

Technology Development and Evaluation

In the early stages of the development, operators provided significant guidance and support through structured reliability and technical-assurance processes involving technical reviews, reliability and risk appraisals, and value assessments. The technology was viewed as promising for application to deepwater long-distance tiebacks. Reducing the size and weight of the surface units would enable tying fields back to congested existing facilities. There is potential use for subsea high-integrity pressure-protection systems. Synergies would exist with other electrically powered applications such as operation and maintenance of subsea-processing systems, heat-tracing systems, and resident remotely operated vehicles.

A pilot project on a reduced-risk favorable field case was planned. Study results obtained from the single-well shallow-water case demonstrated a 31.8% reduction in lost-production days per year (including intervention and repair time) over a 20-year life. This reduction translated into a 26.7% decrease in the cost of deferred production in favor of the all-electric system. Production availability increased by 2% (from 94.4% for the EHM system to 96.4% for the all-electric SPS). Similarly, the results from the single-well ultradeepwater case showed a 27.8% reduction in lost-production days per year (20-year field life), with a corresponding 22.2% decrease in deferred-production costs.