It is very common in the oil & gas plant to control its oil or gas well through a wellhead control panel (usually called WHCP). Each well is always equipped with a SCSSV (Surface Controlled Sub-surface Safety Valves) or usually it is called as down hole valve (DHV) and a SSV (Surface Safety Valves) which is consist of a Master Valves (MV) and Wing Valves (WV). SCSSV in most application is an on-off valve with hydraulic actuators. While SSV can be driven by hydraulic actuator or pneumatic actuator depends on the pressure rating. It is also a need to open or close SCSSV and SSV in sequence and accommodate an Emergency Shutdown signal from the systems. So what are WHCP and its essential component? This article tries to explain the WHCP systems in general application and how it works.
See the general overview of WHCP systems at the end of this article as a general guidance. WHCP systems usually consist of hydraulic reservoir, strainer, hydraulic pumps, accumulator, wellhead control module, and hydraulic line which are supply and return to wellhead control module. Any other parts except wellhead control module are classified into basic cabinet. Each control module is built up dedicated for one well only. Therefore if there are 5 well in a wellhead platform, then there will be 1 basic cabinet and 5 wellhead control module needed.
First part of WHCP is a hydraulic reservoir. This reservoir contains hydraulic fluid in sufficient quantity to operate each wellhead. The size of reservoir is determine through an estimation of hydraulic fluid needed to operate each actuator, possible leakage, distance from the well, and an additional safety factor. Usually the hydraulic reservoir is an atmospheric tank with a flame arrestor venting.
To build up a hydraulic header (high or medium pressure) the WHCP utilize a hydraulic pump. In general the SCSSV will operate at high pressure rating and SSV will operate at medium pressure rating. Thus there will be two hydraulic headers at WHCP with its own hydraulic pump. The hydraulic pump can be pneumatic driven or electric driven depends on criticality and operation area. All hydraulic pump suction will have a strainer to filter the hydraulic fluid from any particulate so that the hydraulic fluid goes to SCSSV or SSV is clean. To make the hydraulic demand from SCSSV or SSV achievable, the downstream of the hydraulic pump (hydraulic header) is equipped with an accumulator. It helps the hydraulic pump to supply quickly the hydraulic demand. This arrangement (reservoir, hydraulic pumps, and accumulator) usually is called as a hydraulic power pack or a hydraulic power unit.
After the hydraulic fluid accumulated at the hydraulic header (both high pressure and medium pressure) then it’s ready to supply each wellhead control module. Usually the line from hydraulic header to wellhead control module is called a hydraulic supply lines. At this wellhead control module, the sequence and logic to operate the SCSSV and SSV is built up. The ESD signal mainly also goes to this module. When it needs to open the SCSSV and SSV, it supplies the high pressure or medium pressure hydraulic fluid to the SCSSV and SSV. In case there is a need to close it down, the hydraulic fluid supply will close and the hydraulic fluid will goes to a hydraulic return line through a three way valves selector. This hydraulic return line will goes to the hydraulic reservoir again.
From this general explanation we can conclude that the wellhead control panel (WHCP) is a hydraulic system that utilizes a hydraulic power pack and a wellhead control module to perform its task. The output of WHCP is high pressure hydraulic supply and medium hydraulic supply to operate SCSSV and SSV. Wellhead control panel is also the interface between the plant control and safety system with the SCSSV and SSV systems.
Article Source : Instreng