Investigating the Effects of Heterogeneity, Injection Rate, and Water Influx on GAGD EOR in Naturally Fractured Reservoirs

The gas-assisted gravity drainage (GAGD) process is designed and practiced based on gravitydrainage idea and uses the advantage of density difference between injected CO2 and reservoir oil.In this work, one of Iran western oilfields was selected as a case study and a sector model wassimulated based on its rock and fluid properties. The pressure of CO2 gas injection was close to theMMP of the oil, which was measured 1740 psia. Both homogeneous and heterogeneous types offractures were simulated by creating maps of permeability and porosity. The results showed thathomogeneous fractures had the highest value of efficiency, namely 40%; however, in heterogeneousfractures, the efficiency depended on the value of fracture density and the maximum efficiency wasaround 37%. Also, the effect of injection rate on two different intensities of fracture was studied andthe results demonstrated that the model having higher fracture intensity had less limitation inincreasing the CO2 injection rate; furthermore, its BHP did not increase intensively at higherinjection rates either. In addition, three different types of water influxes were inspected on GAGDperformance to simulate active, partial, and weak aquifer. The results showed that strong aquifer hada reverse effect on the influence of GAGD and almost completely disabled the gravity drainagemechanism. Finally, we inventively used a method to weaken the aquifer strength, and thus thegravity drainage revived and efficiency started to increase as if there was no aquifer.

Keywords:

Gravity Drainage , Naturally Fractured Reservoirs , GADG , CO2 Gas Injection , Heterogeneity , Fracture Intensity