Page 134 - Well Control for Completions and Interventions

126 Well Control for Completions and Interventions

to the well. Careful installation and management of subsurface valves can
help improve reliability.

3.19.1 Subsurface controlled valves
Subsurface controlled subsurface safety valves (SSC-SSSV) are, as the name
suggests, operated by flow (or injection) parameters below the surface. In
simple terms, they close if flow velocity exceeds a predetermined value.
These types of valves are run postcompletion, and are usually set in a con-
ventional nipple profile. There are two types of valve for production wells.

3.19.1.1 Pressure differential safety valves
Pressure differential valves are normally an open valve. If flow velocity
across an internal choke exceeds a predetermined velocity, the pressure
drop across the choke will be sufficient to force piston travel against the
operating spring. Piston movement will close the valve. Opening the
valve requires pressure to be equalized from above (Fig. 3.32).

Figure 3.32 Flow-operated safety valve (storm choke). Image courtesy of Halliburton.