EXTRACTION OF FLUIDS FROM WELLS

A control system (106) is provided for controlling the flow of hydrocarbons out of a production well. The control system has hydraulic decoders which operate a plurality of chokes. The hydraulic decoders (124) provide actuation signals on receiving hydraulic control pressures within predetermined ranges. The actuation signals operate a hydraulic actuator (120) to open or close a particular choke. In this way chokes can be operated independently. Hydraulic control lines (128) are consolidated by a shuttle valve (134) into a single control line (136). Valves (138) (140) are configured so that, in the absence of control supply (136), valve (138) is closed and valve (140) is open. Valve (138) opens at 1,000 psi and, since valve (140) is open, hydraulic power supply (148) is transmitted through decoder (124) to operate actuator (120) and thus the choke. When the pressure increases above 1200 psi the valve (140) closes. Valves (142) (144) are operated by a pressure between 1500 psi and 1700 psi so that the actuator can move the choke in the opposite direction.