7 - Subsea Control

Abstract

The subsea control system operates the valves and chokes on subsea trees, manifold/templates, and pipelines. It also receives and transmits the data between the surface and subsea, which helps engineers monitoring the status of production by indicating temperatures, pressures, sand detection, etc. The location of control devices is extremely important. Careful consideration to the location of controls can result in a reduction in the amount of piping and cabling and the number of connections required, which in turn influences the subsea installation and retrieval tasks. The typical control elements include the following: topside: electrical power unit, hydraulic power unit, master control station, topside umbilical termination assembly; subsea: umbilicals, subsea umbilical termination assembly, electrical and hydraulic flying leads, subsea control module, etc. The fundamental purpose of a control system is to open and close valves. However, other properties, such as instrumentation, provide chock control and important diagnostics. The five types of fundamental control systems are direct hydraulic; piloted hydraulic; sequenced hydraulic; multiplex electrohydraulic; and all-electric. The simplest remotely operated system for control and monitoring of a subsea system is the direct hydraulic control system. In this system each valve actuator is controlled through its own hydraulic line. This system is typically used for workover applications and small systems and is especially common in single-satellite oil/gas fields of distances less than 15 km.