Relative permeability hysterisis effect of Water-Alternategas (WAG) injection

Abstract

Water Alternate Gas (WAG) injection enhanced oil recovery is said to recover nearly all residual oil where the water and gas sweeps alternately. It has been shown that combining water and gas injection in a WAG (water alternating gas) scheme can result in additional oil recovery from 5% to 10%. Interest in WAG injection has increasingly grown in recent times with many reservoirs around the world now is under WAG injection. In cases of limited rate of injection pressure, the key to overcoming gravity override by gas is the injectivity itself while in the cases of attic oil or cellar oil recovery, the key to exploiting the oil is the increased microscopic displacement efficiency by using water alternate gas injection method. Numerical simulation of WAG requires reliable three-phase relative permeability and hysteresis data which are normally obtained from models available in commercial simulators. This thesis utilizes real reservoir data to investigate the effect of relative permeability hysteresis of WAG injection simulation models using ECLIPSE (E300). By considering relative permeability hysteresis in WAG simulation, it helps to increase the oil recovery prediction as much as 11%. This is because hysteretic model accounts for the gas trapping effect during cyclic changes in saturation. The gas trapping effect is actually a beneficial process as it reduces the gas permeability, hence reduction in gas mobility. As a result, this will lead to better oil recovery. Hence, WAG injection can lead to improved oil recovery by combining better mobility control and contacting unswept zones, and by leading to improved microscopic displacement. The result of this work shows that a good understanding of the relative permeability hysteresis model in use is very important for a more robust reservoir simulation model for an optimum design of EOR facilities in the future.