WHCPs are also known as Shutdown Panels (SDP), Emergency Shutdown Systems (ESD), or Hydraulic Safety Shutdown System (HSSS). These are failsafe shutdown systems which have pneumatic/hydraulic/electric components; WHCPs can also be integrated with PLC/ RTU/ SCADA. WHCPs are standalone control systems as well as an interface between the plant control and the wellhead safety system. WHCPs are used for monitoring, controlling (Remote/Local) and safe shutdown of Subsurface Controlled Safety Valves (SCSSV), Surface Safety Valves (SSV), and other wellhead safety valves (Choke, ESD, HIPPS) in oil & gas production fields to ensure safe operation of unattended wells/platforms.
WHCPs may have multiple applications, which include, but are not limited to
- Safe and Sequential Operation of Wellhead Valves (SCSSV/SSV/Wing Etc.)
- Emergency and Fire Shutdown
- Safe Operation of Riser Valves
- Flowline Pressure control
- Well Test Operation
- HIPPS /ESD/ Choke Valve Control
- Partial Stroking
Overview of Wellhead Control Panel
Gas wells and oil wells have a high potential hazard, either because the material ejected flammable or the potential hazard of the gas pressure is high. The wellhead control panel is key equipment in the oil & gas industry to protect oilfield facilities and the environment from occurring wellhead fire and emergency incidents, which is one of the main control systems to ensure oilfield oil production and transportation to be safely operation according to international standards and national regulation. Its function is to shut down the well in case conditions that harm or for other interventions as well as the work test, etc.
The wellhead control panel is composed of a hydraulic power unit (HPU), tubing & fitting, and instrument valve and electrical control devices. HPU supplies hydraulic resources to open and close SSVs including MSSV, WSSV, and SCSSV.
The level of complexity of each well head control panel varies, each company has its own standard. So the definition of well head control panel, in General, will certainly vary, the definition well head control panel if we review of its functionality is part of the surface facilities of the gas well or an oil well that is used to control well, like: be it to shutdown system, the casing pressure reading parameters, tubing pressure reading parameters, temperature well parameters. So to open or close a Wing Valve (WV), Master Valve (MV), as well as Down Hole Safety Valve (DHSV) can be through the Wellhead control panel. Generally inside wellhead control panel consists of control pneumatic or hydraulic. Control pneumatic or hydraulic composed of tubing and three-way valve.
Here I will only discuss WHCP from gas wells, as I understand. Function or application WHCP depending on each type of wellhead control panel. It is a simple system until it is tricky. If it can be inferred is actually a function of well head control panel is to operate well, be it for shut-in and POP (put on production). With the wellhead control panel we able to open or closed the DHSV via the push button in the panel. Also, we can open or close a master valve or wing valve with push-button in the panel as well. It was all done manually, by pressing or pulling a push button. But to close the DHSV, Master valve, Wing Valve can be done automatically, namely through the integration with the shutdown system from the well. Surely this should follow the philosophy of the shutdown system used by each company.
By looking at the picture, it will give an overview of what functionality or usability of the wellhead control panels. The components are visible in the picture can be grouped into:
All of these components will give feedback or as an input signal to the Wellhead control panel (WHCP). While in the well itself (flowline) there is a sensor that is used to monitor the condition of the well, either to shut down the system, or just for readability only.
Instrumentation for shutdown system e.g.:
- PALL (pressure switch low low)
- PAHH (pressure switch high high)
- The Fusible plug (for detection of fires), usually mounted above fangles or parts that there is a possibility of leaks (the source of fire)
The instrumentation used for reading, for example:
- FR (flow recorder) or Flow Indicator
- PR (pressure recorder) or Pressure indicator
- TR (temperature recorder) or Temperature Indicator
The final element of the system shutdown:
- DHSV, Down hole Safety valve ( drived by hydraulic power)
- MV, master valve (drived by hydraulic power)
- SSV, surface safety valve (drived by pneumatic power)
- Choke valve, manually operated
- SDV (shutdown valve) installed in flow line of well, outside the part of the wellhead (X-mastree)
Valves are a part of which will receive command of the signal to be opened or closed from Wellhead control panel. So if I can give analogical WHCP is a controller (a control system), SSV, MV, DHSV, SDV are the part that receives the output from the controller, while the PALL, PAHH, fusible plug is the input of the controller. But don’t imagine WHCP like PLC in General. WHCP I discuss here is that it uses control pneumatic or hydraulic.
Why WHCP generally uses pneumatic control, because most of the well gas wells far location (remote) so hard to find sources of energy such as electricity. And generally WHCP from gas wells using gas from the well itself as a source of pneumatic power. Later will be discussed where the pneumatic power source to run the WHCP. With pneumatic power from gas, we can also have hydraulic power, i.e. by installing the hydraulic pump on run by pneumatic power. Hydraulic power is used to run the valve actuator which relatively large power needs. Pneumatic-powered convert hydraulic power can become larger by using the pump.
The Problems That Often Arise in Wellhead Control Panel (WHCP)
From the various experiences, The problems that often arise in WHCP are leaking, popping, and stuck. Commonly Leaking occurred in the connection of nuts on the tubing. It could be leaking at three-way valve components. To this, we can issue leaked retighten the bolts or given a Teflon sealant. If for three-way valve usually replace the internal parts like its o ring, whereas in order to overcome stuck at a three-way valve do greasing of the internal plunger. Stuck in a 3-way valve because it is dirty or arid.
For ordinary problems, popping occurs at PSV. PSV is a safety equipment to handle excess pressure. Each panel of a pneumatic or hydraulic there must have been his PSV. Just like in the WHCP. When there is excess pressure, PSV will popping, release the excess pressure. When it was popping PSV unbiased back to its normal position, the problem is often the case. To fix this we clean the inside and then check the setting.
One of the disadvantages of pneumatic systems that use hydrocarbon gas as a source of power instrument is if the liquid into a pneumatic system. This will cause the three-way valve not working well. If the wrong selection of the material, for example, the O ring not resistant to hydrocarbon substances, will certainly damage the o ring itself.
Main Function of WHCP
- Local On/Off SSV
- Remote control SSV through RTU
- High-Low pressure sense shut-down automatically.
- Fusible Plug, Anti-fire Shut-down automatically.
- SSV can not be opened unless local reset after shutoff
- The function of showing system pressure
- Relief Valve shall be installed on each hydraulic circuit to prevent high pressure
- The function of showing hydraulic level and level switch for alarm
- Function of defending pressure impact of system
- Function of defending exorbitant pressure
- Function of system pressure monitoring(by pressure transmitter of the control panel)
- Function of remote emergency shut-down (by the magnetic valve of the control panel)
- Function of On/Off SSV monitoring (by pressure switch of the control loop of the control panel)
- Function of shield High-low pressure sense
Types of WHCP
Single wellhead Control Panel
wellhead control panel is used for controlling one well Surface controlled sub-surface safety valve (SCSSV), Master SSV, and Wing SSV. SSVs can be shut down automatically and manually by WHCP to respond to all kinds of emergency situations.
The single well control panel is categorized the following system according to driven resource:
- Manual control system
- Electrical control system
- Pneumatic control system
- Solar-powered control system
Manual control system
Feature and Function: Manual hydraulic pump supplies hydraulic control and output pressure for SSV. The main function includes Remote ESD, Fusible plugs, low pressure / high-pressure sensing, Manual shutdown at the panel.
Electrical control system
Feature and Function: Electrical motor-driven hydraulic pump with a manual pump as standby will supply hydraulic to control SSV. The main function includes Remote ESD, Fusible plugs, low pressure / high-pressure sensing, Manual shutdown at the panel.
Pneumatic control system
Feature and function: Pneumatic driven hydraulic pump with manual pump as standby will supply hydraulic to control SSV. The main function includes Remote ESD, Fusible plugs, low pressure / high-pressure sensing, Manual shutdown at the panel.
Solar-powered control system
The solar-powered control system is designed to be used for wellhead control located in a remote areas and desert areas.
Feature and Function: Energy conservation, Reduce operation expense, Duel power supply, Standard control feature
Main function includes RTU shutdown；Fusible plugs；Low pressure/high-pressure ；Local Manual control
Multi-wellhead Control Panel
Each control module is drawable and can be inter-replaceable without any interruption of other well operation. The common module includes oil reservoirs, Pneumatic hydraulic pump,s, and standby manual pump.
The main function shows as following: Remote RTU shutdown; Fire fusible plugs protection, Low pressure / high-pressure sensing, Manual control at the panel.
Well Head Control Panel Working Principle
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 an SCSSV (Surface Controlled Sub-surface Safety Valves) or usually it is called a down hole valve (DHV) and an SSV (Surface Safety Valves) which is consist of a Master Valves (MV) and Wing Valves (WV). SCSSV in most applications is an on-off valve with hydraulic actuators. While SSV can be driven by a 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 the general application and how it works.
WHCP systems usually consist of a hydraulic reservoir, strainer, hydraulic pumps, accumulator, wellhead control module, and hydraulic line which are supply and return to the wellhead control module. Any other parts except the wellhead control module are classified into the basic cabinet. Each control module is built up dedicated to 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.
The first part of WHCP is a hydraulic reservoir. This reservoir contains hydraulic fluid in sufficient quantity to operate each wellhead. The size of the reservoir is determined 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 utilizes a hydraulic pump. In general, the SCSSV will operate at a 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 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 the hydraulic header to the wellhead control module is called the hydraulic supply lines. At this wellhead control module, the sequence and logic to operate the SCSSV and SSV are 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 go to a hydraulic return line through a three-way valves selector. This hydraulic return line will go 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. The wellhead control panel is also the interface between the plant control and safety system with the SCSSV and SSV systems.