The increasing global demand for energy has necessitated the exploration of untapped potential energy resources. Unconventional oil reservoirs present a significant opportunity for development through various enhanced oil recovery (EOR) methods. Among these methods, the huff’n’puff scheme using Carbon Dioxide (CO2) EOR has emerged as a potent technique, considering both productivity and its impact on global warming. Unlike water injection, CO2 EOR exhibits high injectivity potential in tight formations, making it a promising approach.
This thesis focuses on investigating the performance of CO2 EOR in unconventional oil reservoirs using the huff’n’puff scheme through a comprehensive reservoir simulation study based on an open-source geological model. The study evaluates the effects of key parameters on oil production, including injection rate, injection time, soaking time, diffusion coefficient, and well completion.
The simulation results demonstrate that CO2 EOR can effectively enhance oil recovery from unconven- tional oil reservoirs. Specifically, the study reveals that implementing CO2 EOR increases cumulative oil production by 27% after 20 years compared to natural depletion cases. Furthermore, when incorporating a two-year primary recovery period, cumulative oil production is further elevated to 45%. By implementing the findings from the sensitivity study, cumulative oil production can be increased up to 67% in the optimum case.
In terms of the influence of the tested parameters on oil production, the study identifies that higher injection rates and longer injection, soaking, and production times for each cycle improve oil recovery until reaching an optimum value. Additionally, extending injection period by 10 times in each cycle with the same CO2 injected volume improved cumulative oil production by 7% compared to fixed injection rate as a result of longer diffusion and dissolution time. Moreover, implementing bottom CO2 injection targeting bottom layers improves vertical sweep efficiency due to buoyancy forces. The study also highlights the importance of the diffusion coefficient, as higher values facilitate faster CO2 transport, resulting in higher oil recovery and reduced CO2 reproduction.
This thesis provides valuable insights into the design and implementation of CO2 EOR projects in tight oil reservoirs. It emphasizes the need for careful selection of optimal operating conditions based on specific reservoir properties and highlights the significance of the diffusion mechanism in CO2 EOR performance. The findings contribute to the development of more effective CO2 EOR strategies for unconventional oil reservoirs, addressing gaps in previous research. Moreover, the study’s outcomes have practical implications for improving the design and implementation of CO2 EOR projects in the field, ultimately leading to increased oil production.