Research and simulation study of different technological processes of miscible CO2 water alternating gas injection

One of the most commonly used methods for EOR in recent years is the water-alternating-gas (WAG) method, WAG injection is an oil recovery method aiming to improve displacement ratio, sweep efficiency and adjust the alignment of displacement in different layers to improve oil recovery and pressure maintenance. The main mechanism of it is 1) bettering the mobility control, 2) improvement of sweep efficiency (comparing to gas methods) and 3) the displacement efficiency (comparing to waterflooding). Many studies have been done in the past, but due to the increasing hard-to-recover field and facing difficulties during the production, the traditional WAG is facing problems that need to be coupled with. Implementation of new combinational methods and changes in the injection process to meet the needs have been developed during the last two decades. In this study, a simulation investigation has been done to compare proposed changes in the injection process to find the optimal injection scheme for the high heterogeneity - low permeability field. After analyzing the output of the simulation, the results show that each of the technologies has its advantages and disadvantages, and need to be applied according to the field constraints and requirement. Keywords: water alternating gas (WAG); enhanced oil recovery; reservoir simulation; injection scheme; heterogeneity; permeability.