The Effect of WAG’s Starting Injection Time to Oil Recovery in Inverted5 Spot Simulation Model

Abstract

Water Alternate Gas (WAG) method have been used to enhance the displacement effectiveness of CO2 injection mechanism. CO2 injection was used to increase additional oil recovery by swelling the volume of oil and reducing its viscosity. By adding water after CO2 injection phase, it will increase the volumetric displacement efficiency thus improving mobility ratio and increasing oil  recovery. In this study, the determination of water injection start time after CO2 injection will be further investigated to improve oil recovery of simulation results.

This simulation was using analogue 3D model from X Field with the wells used in this study are existing wells. It will be simulated by using CMG GEM commercial simulation software. The reservoir target layer for CO2 injection is at Y Layer, Talang Akar  Formation. Current reservoir pressure of Y Layer is at 2500 psia with the MMP of the oil is at 2900 psia. The inverted 5 spot pattern injection scenario will be done for 15 years with WAG injection is conducted after the primary recovery. Several scenarios which consist of injecting water before CO2 breakthrough, slightly after CO2 breakthrough, and after CO2 breakthrough were done with using same injection rate of CO2 and water. CO2 rate was at 3.6 MMSCFD and water rate is equivalent with the CO2 injection rate. The effect of the water injection starting time then was analyzed.

The result of the study is that injection water after CO2 breakthrough is giving the best result with RF of 40.13%, compared with  the water injection before CO2 breakthrough (RF 39.47%) and injecting water slightly after breakthrough (RF 39.68%). By injecting water after CO2 breakthrough will give more time for the microscopic displacement take effect and CO2 phase can contact more oil before water displace the leftover oil which cannot be swept using CO2 injection.