A Subsurface Safety Valve (SSSV) is a safety device installed downhole in an oil or gas well to prevent uncontrolled flow of fluids in the event of an emergency. It can be operated from the surface (Surface-Controlled SSSV) or by downhole conditions (Subsurface-Controlled SSSV).

Key Features and Functions:

Emergency Shutdown:

The primary function of an SSSV is to shut off the flow of fluids from the wellbore in case of a safety issue, like a leak or blowout.

Fail-Safe Design:
SSSV systems are typically designed to be fail-safe, meaning they will automatically close and isolate the wellbore if control pressure is lost or there’s a system failure.

Surface or Subsurface Control:
Surface-Controlled SSSVs are operated from the surface via a control line, while Subsurface-Controlled SSSVs react to pressure changes or other downhole conditions.

Retrievability:
SSSVs can be either wireline retrievable (components can be retrieved without pulling the entire tubing string) or tubing retrievable (requiring removal of the entire tubing string for access).

Types of SSSVs:
Surface-Controlled Subsurface Safety Valve (SCSSV):
These valves are operated remotely from the surface, often using hydraulic pressure or electrical signals to control their open/closed state.
Subsurface-Controlled Subsurface Safety Valve (SCSV):
These valves are designed to react to downhole conditions, such as pressure changes, to automatically shut off the flow.