Experimental and Modeling Study of CO2 EOR and CO2 Storage in Heavy Oil Reservoirs

Abstract

This study focuses on unveiling the interaction between injected CO2 and heavy oil through adequate phase behavior analyses. Moreover, the potential of CO2 EOR and CO2 storage were evaluated through injection scheme optimization and sensitivity analysis. Experimentally, the PVT experiments including CO2/heavy oil systems have been carried out to measure oil swelling, solubility, viscosity reduction, and density variation. The MMP of the heavy oil-CO2 mixture has been determined to provide the reference pressure for core displacements. CO2 injection experiments were conducted to examine the performance of CO2 enhanced recovery under different pressure. Different injection schemes were experimentally simulated including water flood, injection water followed by CO2 flooding, and injection water followed by CO2-WAG (water alternating CO2 flooding). Based on these studies, the sensitivity analysis was run on the validated model to examine the effects of different parameters including gas injection rate, CO2 slug size, and CO2-WAG cycle number on the heavy oil recovery and CO2 storage efficiency. As the saturation pressure of the heavy oil-CO2 mixture increases, the solubility of CO2 in heavy oil, the swelling, and the viscosity reduction increase at reservoir temperature (60°C). Although CO2 displacement efficiency and CO2 storage efficiency increase with increasing injection pressure, the increase in these two factors become significantly slower as pressure exceeds the MMP (30 MPa). Injection water followed by CO2-WAG increased oil recovery more than water flood or injection water followed by CO2 flooding. Only considering the influence of single factor conditions, the higher the injection CO2 rate, CO2 slug size, or WAG cycles number, the higher the cumulative oil production. However, based on comprehensive consideration of oil displacement rate, CO2 storage efficiency, CO2 cumulative storage, and cumulative WOR (water-oil ratio), reasonable injection CO2 rate, CO2 slug size, and WAG cycles number were finally optimized and screened out as 30,000 m3/day, 0.5 PV, and 5, respectively. The outcomes of this work provide valuable information for designing a suitable CO2 flooding strategy in heavy oil reservoir engineering applications. It also could bring significant economic and environmental benefits by improving oil recovery and reducing CO2 emissions.