Choke valve is a type of control valves, mostly used in oil and gas production wells to control the flow of well fluids being produced. Another purpose that the choke valves serve is to kill the pressure from reservoir and to regulate the downstream pressure in the flowlines. Choke valves allow fluid flow through a very small opening, designed to kill the reservoir pressure while regulating the well production. The reservoir fluids can contain sand particles. Hence the choke valves are usually designed to handle an erosive service.
Typically oil and gas producing wells have two choke valves in series, one non-regulating choke valve and one regulating choke valve downstream to the non-regulating choke valve.
Non-regulating choke valves
Function of the non-regulating choke valve is to act as an on-off valve and kill the reservoir pressure to a desired operating value in the flowline. The opening in the choke valve is sized to kill the pressure when valve is fully open. The non-regulating choke valve is not used for flow regulation and hence is not sized for controlling the flow. Over the life of an oil production well, the reservoir pressure drop as fluids are depleted from the reservoirs. Hence with dropping reservoir pressure, the non-regulating valves may have to be changed to maintain the same well production levels. Hence over the life of an oil production well, the non-regulating choke valves can be replaced with valves having increasingly larger openings for flow.
Regulating choke valves
The regulating choke valve is a flow control valve which is designed to maintain a steady production level in the flowlines and production header. Regulating choke valve is an automatic valve and valve opening can be controlled via electric or pneumatic signal from the control panel to regulate the flow in downstream flowlines.
Among other applications, choke valves can be used liquid lines operating at very high pressures.