DHSV is an abbreviation for “Downhole Safety Valve”. DHSVs are considered as one of the important and critical objects during the completion process of a well as these are fail-safe devices that act immediately to prevent an uncontrolled hydrocarbon fluid release that causes an immediate surge in the pressure inside the wellbore and creates a situation of blowout.

DHSVs can move only in one direction i.e. either close or open position. When these valves are closed they completely isolate the reservoir fluids from the surface. These valves are hydraulically operated from the control panel located at the surface. When hydraulic pressure is applied down a control line, the hydraulic pressure forces a sleeve within the valve to slide downwards. Because of this hydraulic pressure, the flapper of the valve is compressed downwards thereby opening the valve. When the hydraulic pressure is released, the spring pushes the sleeve back and causes the flapper to shut.

The downhole safety valves are surface controlled sub surface safety valves abbreviated as (SCSSV or SVSSVs). There are two basic types of SCSSV:

•          Wireline Retrievable surface controlled sub surface safety valves (WR – SCSSV) and
•        Tubing Retrievable surface controlled sub surface safety valves (TR – SCSSV)