Evaluation of in-situ gas lift using numerical reservoir modeling

Abstract

Small oil reserves which are located in remote area or offshore are challenging to develop due to economic reasons. In this case, in-situ gas lift can be used to lift the oil where relatively high pressure gas is available. This method does not need pipeline for lift gas and gas compression facilities. Thus, it is cost effective. The purpose of this study is to determine variables that affect to in-situ gas lift and make guideline for reservoir condition whichare suitable for this method. This study starts with constructing the reservoir model using reservoir simulation and vertical flow performance. The model is simulated with natural depletion case first; then we investigate the effect on gas lift performance of several variables which are: (1) permeability of gas bearing zone (2) perforation interval of gas bearing zone (3) depth of gas bearing zone (4) thickness of gas bearing zone and (5) water aquifer in the oil zone. From the results of reservoir simulation, low permeability of gas zone results in better recovery factor. For high permeability and high thickness of gas reservoir, reducing perforation interval helps increase the oil recovery factor. Regarding the depth of gas bearing zone, shallow depth provides the lowest oil recovery factor. However, there is no significant difference in oil recovery factor for cases with different of thicknesses of gas zone. Oil reservoir with aquifer has lower oil recovery factor than the one without aquifer.