Process Control

Wellhead Control Panel

  • The wellhead, often nicknamed the Christmas tree due to its distinctive shape, acts as the uppermost connection point of a well to the reservoir.
  • Oil or gas travels through the well bore, enclosed by casing, with the decision to install the wellhead based on its economic viability.
  • Within oil fields, the wellhead is pivotal, housing valves and equipment essential for regulating pressure and flow to prevent hazardous conditions stemming from the release of flammable materials and high internal pressures.
  • Well Head Control Panels (WHCP) are employed to ensure controlled and fail-safe flow through the wellhead.
  • The Christmas tree structure comprises various safety valves, including Subsurface Controlled Safety Valves (SCSSV), Surface Safety Valves (SSV), alongside others such as Choke, ESD, and HIPPS.
  • These valves serve the purpose of shutting off the well when necessary to mitigate risks.
  • Additionally, a pressure gauge situated at the tree’s apex provides an indication of tubing pressure.
  • The operations within the wellhead are managed and regulated through the use of three valves, in conjunction with gauges and a choke.
Well Head Control Panel
  • A Well Head Control Panel (WHCP) is a critical component used to monitor and manage the safety valves within the wellhead. 
  • Its primary purpose is to ensure the safety of the well by preventing risks to personnel, the environment, and equipment. 
  • WHCPs are designed to be fail-safe, typically programmed and controlled by Programmable Logic Controllers (PLC) or Supervisory Control and Data Acquisition (SCADA) systems. 
  • WHCPs receive input signals from various gauges installed in the wellhead, including pressure, temperature, and flow gauges. 
  • Additionally, inputs are received from emergency shutdown systems (ESD), emergency pushbuttons, and fusible plugs. 
  • Based on these signals, the WHCP generates output commands to shut down the valves on the wellhead, thereby ensuring the safety of the plant. 
  • These control panels employ both hydraulic and pneumatic components. Subsurface Controlled Safety Valves (SCSSVs), commonly used on land wells, are typically operated hydraulically. 
  • In such cases, the WHCP includes a hydraulic reservoir and pump system to maintain pressure on the subsurface valves during normal operation. 
  • Surface Safety Valves (SSV), on the other hand, are controlled using pneumatics. Hence, the WHCP integrates various control systems to enable controlled operations and emergency shutdowns. 
  • For land wells operating under high pressure, separate wellhead control systems are used for each well. 
  • However, for offshore platforms, wellhead control systems are grouped onto one or more panels. 
  • Each well’s control logic is kept distinct to facilitate the addition or removal of wells as needed.
Main functions of Well Head Control Panel 1
  • Well Head Control Panels (WHCP) come in various types, including electric, manual, solar-powered, and pneumatic controlled panels, chosen according to specific application requirements.
  • WHCP manages oil and gas wells by controlling valves at the wellhead, including SCSSV (Surface Controlled Sub surface Safety Valves) and SSV (Surface Safety Valves) consisting of Master Valves (MV) and Wing Valves (WV).
  • The sequential operation of SCSSV and SSV facilitates the Emergency Shutdown (ESD) process for safety.
  • Components of WHCP include a hydraulic reservoir, strainer, hydraulic pumps, accumulator, wellhead control module, and hydraulic lines, determining the size based on fluid requirements and distance to the well.
  • SCSSV and SSV operate at hydraulic pressure, with SCSSV at high pressure and SSV at medium pressure.
  • A hydraulic power pack or unit, comprising reservoir, pumps, and accumulator, meets pressure requirements.
  • Each wellhead has two hydraulic heads and pumps, with strainers to ensure clean hydraulic fluid for SCSSV or SSV.
  • Hydraulics can be pneumatic or electric driven, with an accumulator downstream of the pump to achieve desired pressure.
  • Accumulated hydraulic fluid is supplied through hydraulic lines to the wellhead control module as needed.
  • Sequence and logic for SCSSV and SSV operation are established at the wellhead control module.
  • Signals from the panel control flow or execute the ESD procedure at the wellhead control module.
  • Upon receiving control signals, the wellhead control module opens SCSSV and SSV by sending high and medium pressure respectively, with a three-way valve closing valves and returning hydraulic fluid to the hydraulic line.
  • WHCP ensures effective control of wellhead flow and emergency shutdown procedures in oil and gas operations.

The main functions of a Well Head Control Panel (WHCP) include:

  1. Emergency Shutdown: WHCP is designed to shut down the well promptly in the event of hazardous situations or emergencies, ensuring the safety of personnel, equipment, and the environment.
  2. Critical Parameter Control: It controls critical security parameters essential for safe and efficient well operation, such as pressure, temperature, and flow rates, to maintain operational integrity.
  3. Sequential Start-up and Shutdown: WHCP facilitates the sequential start-up and shutdown procedures of the wellhead equipment, ensuring smooth and controlled operations during routine maintenance or emergency situations.
  4. Monitoring and Control of SCSSV: WHCP closely monitors and controls the operation of SCSSV (Surface Controlled Sub-surface Safety Valves), a critical component for well safety and integrity.
  5. Utilization of Hydraulic Power Units (HPUs): WHCP employs separate hydraulic power units (HPUs) to facilitate hydraulic pumps, accumulators, reservoirs, and other essential components required for effective operation and control of the wellhead equipment.
  6. Special Pushbuttons for Valve Control: Special pushbuttons are incorporated into the panel to facilitate the immediate stopping of wing valves, master valves, and SCSSV when necessary, providing operators with quick and efficient control over wellhead operations.
Main functions of Well Head Control Panel

Components of a Well Head Control Panel (WHCP) encompass a variety of crucial elements, each playing a significant role in ensuring the safe and efficient operation of oil and gas wells:

Components of Well Head Control Panel
  • Responsible for distributing hydraulic fluid at the requisite pressure to headers. The selection of the hydraulic pump is meticulously determined by factors such as the distance to the wellhead, delivery time, and operational demands. 
  • Controlled by the process control system (PLC or SCADA), the hydraulic pump is essential for maintaining optimal pressure levels within the system.
  • Serving as a reservoir for the hydraulic fluid, the oil tank provides the necessary supply for the hydraulic pump. 
  • Strainers positioned at the outlet of the tank ensure that only clean oil is supplied to the pump, thereby preventing potential contamination. 
  • Additionally, a return line from the valves is connected to the top of the tank, facilitating the efficient circulation of hydraulic fluid within the system.
  • An indispensable energy-saving device, the accumulator is utilized to meet the high-pressure demands associated with SCSSV or SSV operation. 
  • Positioned downstream of the hydraulic pump, the accumulator is carefully sized to accommodate varying pressure requirements. 
  • Comprising gas and hydraulic sections, the accumulator is charged with dry nitrogen gas in the gas section, which compresses upon filling with hydraulic oil. This mechanism enables rapid oil discharge upon demand, ensuring swift and efficient valve operation.
  • Regulators play a crucial role in maintaining regulated pressure for each supply header within the system. 
  • Handling high-pressure ranges, regulators are accompanied by relief valves to ensure system safety and integrity. 
  • By regulating pressure levels, these components contribute to the smooth and reliable operation of the wellhead control system.
  • The hydraulic circuit comprises a network of control valves (SCSSV and SSV), hydraulic tubing, and supply headers. 
  • Carefully selected based on pressure requirements, the hydraulic tubing is designed to accommodate high, medium, and low-pressure demands. 
  • Featuring essential components such as check valves, isolation valves, tubes, and fittings, the hydraulic circuit facilitates the controlled flow of hydraulic fluid throughout the system.
  • Instrumentation interface components are essential for monitoring and controlling wellhead activities effectively. 
  • Pressure transmitters installed on hydraulic headers monitor valve operations in real-time, with live status relayed to PLC controllers for centralized monitoring and control. 
  • Additionally, level gauges continuously monitor reservoir levels, ensuring adequate hydraulic fluid supply. 
  • The integration of WHCP with the PLC/SCADA system enables seamless communication and coordination, enhancing operational efficiency and safety. 
  • For ease of maintenance, troubleshooting, and redesigning, a separate junction box is employed, providing a convenient interface for system management and optimization.
  • The electrical interface encompasses the integration of various components essential for the operation and control of motors within the Well Head Control Panel (WHCP). 
  • This includes establishing power connections for the motors, configuring starter control panel wiring, and establishing a control interface to enable remote operation of motors via the Programmable Logic Controller (PLC). 
  • These functions are typically consolidated within an Electrical Junction Box, where essential equipment such as relays, electrical wiring, voltmeters, ammeters, pushbuttons, indicator lamps, Miniature Circuit Breakers (MCBs), contactors, terminals, and other necessary elements are installed.
  • Furthermore, it’s imperative to include ground lugs within the WHCP setup to ensure proper earthing, thereby enhancing safety measures and mitigating the risk of electrical hazards.

Types of Well Head Control Panels (WHCP) encompass a range of configurations tailored to specific operational requirements and environmental conditions:

  • Designed to control a single wellhead, managing all associated equipment and facilitating both automated and manual shutdown procedures.
  • Ideal for remote or solitary wells situated far from other well sites.
  • Further categorized into:
    • Manual Control System
    • Electrical Control System
    • Pneumatic Control System
    • Solar-Powered Control System
  • Utilizes a manual hydraulic pump to supply pressure to the Surface Safety Valve (SSV).
  • Key functions include remote Emergency Shutdown (ESD), fusible plug monitoring, low/high-pressure detection, and manual shutdown capability at the control panel.
  • Employs an electric motor to control hydraulic flow to the SSV.
  • Well-suited for harsh climates or environments with hazardous substances in the flowline.
  • Offers flexibility, ease of deployment, and cost-effectiveness compared to pneumatic systems.
  • Allows seamless integration with Supervisory Control And Data Acquisition (SCADA) systems for remote monitoring and control.
  • Performs similar functions to other systems but utilizes pneumatic energy to control the hydraulic pump.
  • Particularly suitable for high-power operations.
  • Designed for wells located in remote areas, offering energy conservation and reduced operational expenses.
  • Features dual power supply capability and standard control functions.
  • Provides an environmentally friendly and cost-effective solution for remote wellhead control.

Designing a Well Head Control Panel (WHCP) involves careful consideration of various factors to ensure efficient and safe operation:

  • Accurate sizing of components such as the accumulator, tubing, and reservoir is essential for controlled and sequential operation of the wellhead.
  • Designers can utilize specialized software to precisely size components based on given requirements, ensuring optimal performance.
  • Implementation of choke devices at each end of the flowlines is crucial for maintaining safety.
  • Factors to consider for flowline safety include:
    • Distance between the choke device and the initial flowline segment.
    • Requirement for pressure sensors based on distance and shut-in tubing pressure (SITP) compared to maximum permissible working pressure (MAWP).
    • Necessity for pressure relief valves and sensors based on MAWP and SITP disparities.
  • Incorporation of features to facilitate sensor testing, calibration, or replacement is essential for system maintenance.
  • Installation of a three-way valve on the panel enables bypassing of high and low-pressure pilots and sand probes during sensor checks.
  • Panel-mounted indicators clearly indicate when the bypass valve is engaged for safety reasons.
  • Needle valves in supply gas and hydraulic oil tube lines allow for component replacement without the need to shut down individual or all wellheads.

The Wellhead Control Panel (WHCP) can encounter several common problems during operation, including leaking, popping, and getting stuck:

  • Leaks often occur at the connection points of nuts on tubing or within components such as three-way valves. 
  • To address leaks, bolts may need to be retightened or Teflon sealant applied. For three-way valves, replacing internal parts like O-rings can resolve leakage issues.
  • Components like three-way valves may become stuck due to dirt or dryness. 
  • Greasing the internal plunger can help alleviate sticking issues and ensure smooth operation.
  • Pressure Safety Valves (PSV) are safety devices designed to handle excess pressure by popping open to release pressure. 
  • However, if a PSV fails to return to its normal position after popping, it can lead to operational problems. Cleaning the interior of the PSV and verifying its settings can help resolve popping issues.
  • Additionally, pneumatic systems utilizing hydrocarbon gas as a power source may face challenges if liquids enter the system. 
  • This can result in malfunctioning components, particularly affecting the functionality of three-way valves. 
  • Incorrect material selection, such as using O-rings that are not resistant to hydrocarbons, can also lead to damage and system issues. 
  • Regular maintenance, proper material selection, and vigilant monitoring can help mitigate these problems and ensure the smooth operation of the WHCP.

Frequently Asked Questions

A Christmas tree in the context of oil and gas refers to a vertical assembly of valves, gauges, and chokes installed at the wellhead. It serves as a crucial piece of equipment that provides flow control and operational safety on an oil or gas well. The Christmas tree is typically mounted on top of the wellhead and facilitates various functions essential for well operation and maintenance.

  • A wellhead refers to the equipment installed at the top of an oil or gas well, providing support and sealing for the casing strings and controlling the flow of fluids from the reservoir to the surface.
  • A Christmas tree, on the other hand, is a component mounted on the wellhead and serves as a vertical assembly of valves, gauges, and chokes. It provides flow control, pressure regulation, and safety measures for the well operation.

The Christmas tree valve serves several important functions, including:

  1. Flow Control: The valve regulates the flow of fluids from the reservoir to the surface, allowing operators to adjust production rates as needed.
  2. Pressure Regulation: It helps maintain optimal pressure levels within the wellbore, preventing overpressurization or under pressurization.
  3. Safety Measures: The valve can be used to shut off the flow of fluids in emergency situations, ensuring safety for personnel and equipment.
  4. Injection for Stimulation: Some Christmas tree valves allow for the injection of fluids or chemicals into the wellbore to stimulate production or enhance recovery.

The type of valve used in a Christmas tree can vary depending on the specific requirements of the well and the operating conditions. Common types of valves found in Christmas trees include:

  • Gate valves: These valves provide a tight seal when closed and are commonly used for isolation purposes.
  • Choke valves: These valves are used to regulate flow rates by adjusting the size of the flow passage.
  • Ball valves: These valves offer quick and reliable shut-off capabilities and are often used for emergency shutdowns.
  • Check valves: These valves allow flow in one direction only, preventing backflow of fluids into the wellbore.

The selection of the valve type depends on factors such as well pressure, fluid properties, and operational requirements.

Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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