Well installations and subsurface safety valves

Abstract

A subsurface safety valve control system including a downhole stationfor provision in downhole metallic structure () of a well installation which comprises a subsurface safety valve V having an open state allowing flow through the valve and a closed state obstructing flow through the valve. The downhole station () is arranged for picking up electrical signals from the downhole metallic structure () to obtain valve control signals and for outputting control signals for controlling the subsurface safety valve V in dependence on the signals picked up from the downhole metallic structure. The downhole station () comprises a hardware electronics channel () for handling electrical signals picked up from the downhole metallic structure and the hardware electronics channel () is arranged for detecting the presence and/or absence of hold valve open signals. The downhole station () is arranged to cause the subsurface safety valve V to be held in the open state whilst expected hold valve open signals are received and is arranged to cause the subsurface safety valve to move to the closed state in the absence of expected hold valve open signals.