Effect of Gas Injection Pressure on the Performance of CO2-Assisted Gravity Drainage Process in Heterogeneous Clastic Reservoirs

Abstract

Abstract Many simulation studies have been conducted to investigate the effects of various factors on the Gas-Assisted Gravity Drainage (GAGD) process performance. These factors are controllable to constrain the amount of injected gas and produced oil in the vertical injection and horizontal production wells. One of the most recent simulation studies investigated the effects of six controllable factors: maximum oil production, minimum bottom hole pressure, and maximum water cut in the production wells along with maximum gas injection rate and maximum injection pressure in the injection wells. From that study, it has been concluded that the maximum gas injection pressure in vertical injectors has the highest effect on the performance of GAGD process. In this paper, an extensive simulation study was implemented to further evaluate how is dominant the maximum gas injection pressure to enhance the recovery of bypassed oil through the GAGD process. Similar to the aforementioned recent study, the current simulation was carried out on the heterogeneous clastic reservoir (main pay) in the South Rumaila oil field, located in Iraq. The EOS-compositional reservoir flow simulation was adopted to evaluate the effectiveness of CO2–GAGD process under different periodic gas injection pressure levels. Design of Experiments and proxy modeling were adopted to obtain the optimal future oil recovery through changing the pressure in an annual basis. Various what–if–scenarios (simulation runs) were created by the Latin Hypercube Sampling and evaluated by the compositional simulation to find the optimal oil recovery. In the optimization process, the purpose was to search for the optimal future oil recovery by optimizing the levels of periodic gas injection pressure. The optimal cumulative oil production, by the end of 10-year prediction period, reached 4.838 MMMSTB of oil production, while the recent optimal GAGD process resulted to obtain 4.6039 MMMSTB of oil production. Therefore, the current optimization approach has led to increasing the oil recovery by 234.1 million barrels.