Experimental Investigation on the CO2 Effective Distance and CO2-EOR Storage for Tight Oil Reservoir

CO2 underground storage is an important approach to reduce carbon emissions; meanwhile, the combination of CO2 storage and economic benefits can further promote the long-term development of carbon neutrality. Global tight oil reserves are abundant, but the depletion development of most tight reservoirs is unsatisfactory. Therefore, it is crucial to utilize CO2 storage combined with enhanced oil recovery (EOR) for tight reservoir development. At present, there are few experimental studies on the CO2 effective distance and CO2-EOR storage of huff-n-puff in tight reservoirs. In this paper, the CO2 effective distance and the evolution of saturation profiles in tight cores are first investigated, and CO2-EOR storage is quantitatively evaluated for CO2 huff-n -puff in tight reservoirs based on CT and nuclear magnetic resonance technology. Meanwhile, the influences of oil composition and permeability on the effective distance and CO2-EOR storage are further investigated. The results indicate that the increase of CO2 effective distance gradually slows down with time, and the decrease of permeability significantly reduces the effective distance. Increasing amount of oil is mainly produced in larger pores, which is more than twice of that in smaller pores. CO2-EOR storage experiments quantify that the CO2 storage ratio for a 0.22 x 10-3 mu m2 core is up to 72.31% under different depressurization conditions (12, 8, and 0.1 MPa). With the decrease in production pressure, oil recovery gradually increases, while the CO2 storage ratio decreases, indicating that there is a collaborative optimization to maximize the oil production and CO2 storage ratio. Comparison experiments reveal that the oil composition (replaced by fluorocarbon oil) has little influence on the effective distance and CO2-EOR storage, while the influence of permeability is significant. The CO2 effective distance determines the sweep efficiency, so increasing effective distance is essential to enhance oil recovery and CO2 storage. This research is of great significance for CO2 utilization and CO2 storage in tight reservoirs.