the disposal valve 10 into the casing annulus 130 and disposed of through perforations 106 into the water bearing formation 105 the liquid can also be forced into the casing annulus and the accumulated liquid can be 34 u 34 tubed to surface facilities for storage and handling check valve 120 which may be of a tubing or wireline retrievable type is provided to prevent the injection of fluids into the hydrocarbon producing formation 100 referring still to fig1 the controller 108 determines the end of the displacement process by monitoring the pressure differential inside the tubing section 104b using pressure signals transmitted by the pressure transmitters g1 and g2 when it is determined that the pressure differential inside the tubing section 104b is reduced to the desired level gas injection into the supply line 107 is stopped at this point the controller 108 closes valve v1 to stop the gas injection and then opens valve v2 to connect the supply line 107 to the tubing 104 to relieve the gas pressure inside the supply line 107 into the upper section of the tubing 104 the pressure inside the supply line 107 can be reduced further to the desired level by venting gas through valve v4 check valve 112 prevents back flow of gas from the tubing to the atmosphere when.