Volume 56

The Influence of Different Water Quality on Enhanced Oil Recovery by CO2 in Low Permeability Reservoirs Rong Peng, Yong Tang, Youwei He, Jiazheng Qin, Mengyun Liu, Tong Mu

Abstract

CO2 flooding is an effective way to improve recovery factor and achieve CO2 storage. In the late stage of oilfield waterflooding, due to the long-term erosion of injected water, the geological parameters of the reservoir have changed significantly compared with the initial stage, which has a great impact on the distribution of remaining oil. In the conventional reservoir numerical simulation, the changes of reservoir seepage parameters, physical parameters and fluid-related properties over time are not considered, which leads to the fact that the results of the reservoir numerical model are not conform with the actual oilfield development situation and affect the subsequent CO2 flooding effect. Aiming at the problem that the effect of CO2 flooding is not clear after waterflooding in oil reservoir, by using the T-Navigator numerical simulation software, the variation of permeability was characterized by the displacing water multiple. Considering the blockage of suspended solid, oil droplets in different water quality, established a time-varying permeability method for reservoir damage caused by different water quality. Study the influence and reservoir time-varying characteristics of different water quality after waterflooding on enhanced oil recovery by CO2 flooding. The results indicate that: (1) Different water quality in waterflooding can make an impact on CO2 flooding. When the core is damaged by poor water quality, the porosity and permeability decreases. (2) After waterflooding, the average recovery factor by CO2 flooding reduces by 4.54%, the average formation pressure of the injection well increases by 4.56%, the injection capacity declines, the remaining oil saturation rises, and the CO2 spread range decreases. This conclusion is beneficial to selecting appropriate blocks suitable for CO2 injection, and provides a reference for the research on enhancing oil recovery by CO2 flooding after waterflooding in low-permeability reservoirs.

Keywords CO2 flooding, reservoir damage, water quality, numerical simulation, displacing water multiple