Opportunities for the Electric Operation of Valves Associated with Oil & Gas Production
Authors: Matthews Tom C. 
Published: October 2008

The traditional external power source for operating valves associated with offshore Christmas trees and flow lines in oil and gas production has been compressed air or hydraulic fluid. These fluid power supplies and valve actuators have been relied upon to provide the ability to move valves to predetermined safe positions during unusual occurrences or process conditions. As fluid power systems are often complex, requiring frequent inspection and high maintenance, end users and operators of production facilities have long sought a reliable alternative. Efforts to reduce capital expenditures (CAPEX) and operating expenditures (OPEX) coupled with problems associated with hydraulic systems operating in deep water are motivating oil and gas companies to seek alternatives. Electrically powered valve actuators have been used successfully in the North Sea and elsewhere on applications such as mud systems, production test facilities, manifolds and other general applications. However, critical service valves requiring a fail action to a safe open or closed position have historically remained fluid powered. Recent fail-safe electric valve actuator design advances for both topside and subsea applications will provide opportunities to satisfy reliability and economic concerns as well as capitalize on advances in integration with modern digital control systems.

Introduction

Gate valves typically used on wellhead completion equipment or Christmas trees are operated by applying a linear thrust to the valve stem. Commonly automated valves include master valves, wing valves, injection valves and annulus valves, master valves may require wire cutting capability. Some flow line and manifold applications use ball valves, which require a 90-degree rotary input. Hydraulically powered, spring fail-safe actuators have historically been utilized to operate these valves. While the energy required to fail valves to safe positions is sometimes stored in receiver vessels or accumulators, more often, compressed springs are utilized. Hydraulic fluid under pressure exerts force on a piston, which compresses a spring. With this arrangement, the force of the spring is utilized to operate the valve without the need for any external power source. Electric valve actuators have not traditionally been able to fail a valve to a safe position without external power input, requiring an un-interruptible power source. Nor has there been a satisfactory electric motor and spring combination design, which met the safety and reliability demands of the industry. Recent advances in electric valve actuator design which incorporate an internal spring to provide the energy required to move a valve to a safe position will challenge some of the existing traditions of valve control in oil and gas production. Additionally, enclosure sealing issues have been addressed such that an electric alternative will be available for subsea service in deep water.

Technical and Economic Factors

Laws of economics dictate lower cost, shallow water hydrocarbon prospects are the first to be produced. The remaining known undeveloped major offshore oil and gas discoveries are m deep water. Producing these fields presents enormous technological and economic challenges. Using theGulf of Mexico as an example, the ideal subsea design would allow a 60-nule offset from the production platform and 6000foot depth. These parameters would allow floating production to service deepwater GOM discoveries. These extreme distances and depths present problems for traditional hydraulic solutions.