EVALUATION OF DOUBLE DISPLACEMENT PROCESS VIA GAS DUMPFLOOD FROM MULTIPLE GAS RESERVOIRS

Abstract

Double displacement process (DDP) is an efficient method to increase oil recovery by starting with water injection and followed by gas injection. In order to reduce the cost of gas injection units, the concept of gas dumpflood is utilized by using multiple thin gas layers as the gas source. In this study, the effects of the perforation program, operational liquid rates and characteristics of gas reservoirs are evaluated using reservoir simulation. Perforating full to base in all gas layers at the same time provides a higher recovery factor than two-batch perforation because larger amount of gas flows into the oil reservoir at early time. Higher target liquid production rates during waterfood require shorter time to produce oil than lower ones. However, there is not much difference in recovery factors obtained from different target liquid production rates during waterflood. Nevertheless, the target liquid production rate during gas dumpflood needs to be properly selected in order to delay the gas breakthrough and still get high recovery within the time constraint. Larger depth difference between the bottom of the oil zone and the top of gas reservoirs slightly increases the oil recovery factor due to higher pressure and longer support. Regarding original gas in place, higher amount of gas results in higher oil recovery owing to longer pressure support.