A Comprehensive EOR Study of a Highly Fractured Matured Field - Case Study (SPE 153311)

Most of the Middle East fields are approaching their final stage of primary production. Most of these fields are highly fractured and carbonate in nature. One major problem is the creation of gas and water invaded zones during the history of production form such fields. Hence, the implementation of proper EOR process requires an extensive laboratory work. A mature field with more than six decays of production has been considered in this study to explore all possible EOR methods. Several EOR processes such as continuous gas injection (GI), WAG (water alternative gas flooding), SWAG (simultaneous WAG), FAWAG (surfactant WAG), and GAGD (Gas Assisted Gravity Drainage) process were studied in laboratory scale and simulation work. The Gas injection and GAGD were found to be unfeasible due the high fracture frequency and early gas breakthrough even with low rate of injection. However, the WAG, SWAG and FWAG were found to be more feasible. This is possibly due to mobility modification by water phase. During SWAG method all pores displaced at the same time, so that a higher ultimate recovery factor achieved sooner in comparison with WAG process. In order to have better exploration for the residual oil, FAWAG method was applied to control the injectivity of injected gas and reduce the interfacial tension (IFT) between residual oil and rock. Surfactant was chosen in different concentration of 5000, 2000, 1000, 500ppm of surfactant. All experiments were carried out under reservoir condition. The FAWAG process was found to be more suitable process for such reservoirs due to its high recovery. Finally the simulation study was conducted with different patterns of injection and production for all the mentioned EOR scenarios. It was found that the fractures density had an important role in the selection of the optimum pattern.