Benefits of All-Electric Subsea Production-Control Systems

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 17106, "Benefits of All-Electric Subsea Production-Control Systems," by M. Theobald and C. Lindsey-Curran, BP plc, prepared for the 2005 Offshore Technology Conference, Houston, 2-5 May. The oil and gas industry currently is using electrohydraulic subsea control systems as the standard to manage hydrocarbon production from subsea oil and gas fields. While these electrohydraulic controls will continue as the system of choice for the next 5 years, a desire to improve reliability and operational routines will increase the opportunity to use all-electric subsea production-control systems. The first offshore trial of an all-electric subsea production-control system and wellhead tree system was completed recently at the BP Magnus platform in the North Sea. Introduction To produce from greater water depths and harsher metocean conditions, the offshore industry has become technologically sophisticated. This applies both to the floating structures that support topside facilities in water depths greater than 200 m and the tieback technology to produce from long-distance remote step-out wells many tens of kilometers from the host facility. In the early days of subsea tiebacks, each of the hydraulic valves needed to control the flow of hydrocarbons from the wellhead systems was controlled individually by a direct hydraulic connection back to the host facility and a topside control panel. The panel consisted of hydraulic pumps, motors, valves, and accumulators. This was a very successful and reliable concept because of its simplicity and relatively low cost. However, the limitation of direct hydraulics resulted in slow subsea-to-host actuator response times, and this limited tieback distance to approximately 15 km. In addition, the size and weight of the connecting umbilical hoses in all but the simplest of systems resulted in difficulties with transportation and installation. These limitations, together with the increasing requirements to collect reservoir-pressure and -temperature data, prompted the industry to develop more-sophisticated technology, including subsea control systems.