A subsurface safety valve is essentially a shutdown valve installed at the upper wellbore for emergency shutdown to protect the production tubings and wellhead in case of overpressure. Purpose of a subsurface safety valve (SSSV) is to avoid the ultimate disaster which can result in release of reservoir fluids to the surroundings. This makes SSSV a very important component of a well completion.
To protect the surface facilities in case of emergency, the wellbore is isolated from surface facilities using a subsurface safety valve (SSSV). Hence such a safety valve needs to be fail safe in order to isolate well bore in any kind of system failure or damage to surface production, control and safety facilities.
Functioning of SSSV
A subsurface safety valve is typically a uni-directional flapper valve, directed in such a way that the flappers open downwards when pressure is applied from an upward direction. The flapper can only open in the downward direction. So even if high pressure is applied by the well fluids from a downward direction, a safety valve can remain closed. This makes a subsurface safety valve fail-safe. To open the valve, hydraulic signal is sent from the surface well control panel. This hydraulic pressure is responsible for keeping the flappers of SSSV open and loss of hydraulic pressure result in closing of the valve. Thus wellbore can be isolated in case of system failure or damage to the surface facilities.