Wellbores for accessing oil and gas reserves are typically provided with one or more valves or pairs of valves for restricting the wellbore. These valves are used to resist the flow of fluids in the bore and may ultimately be used to close the wellbore, such as BOPs. The valves are used to prevent undesirable exposure of pressurised fluids during the drilling or operation of a well. For example, in a downhole intervention operation, wireline valves allow the well operator to insert and remove tools deployed on coiled tubing or wireline within a wellbore while maintaining pressure in the well.
Wireline valves are intended to stop the flow of a fluid through a tubular or to seal an annular space between two tubulars. Different types of wireline valves, such as annular or blind, are available. For example, blind valves crush or shear tubulars then seal the wellbore.
The valve often comprises a pair of seals that are pressed against each other to prevent fluid flowing through the bore. A valve sometimes has a cutter for shearing equipment such as piping or wireline that may be located in the bore to allow the valve to close to seal off the wellbore.
Wireline valves generally require movement of parts into a pressurised fluid in the wellbore. The valves are usually hydraulically activated, although some valves are mechanically activated.
In order to seal the bore, valve actuators must move parts that are exposed to the wellbore fluid pressure. Fluid pressure in wells can easily exceed 50 MPa and the resultant forces on parts of the valve are typically several tons.