Experimental Investigation of Co2 Storage and Oil Production of Different Co2 Injection Methods at Pore-Scale and Core-Scale

The CO2 storage and oil production of different CO2 injection schemes were investigated using laboratory experiments. Microfluidic equipment was upgraded to increase its working pressure to 15 MPa. Microfluidic experiments of immiscible CO2 injection, miscible CO2 injection, and water alternating CO2 (WAG) injection were conducted. Affected by buoyancy, apparent gas overriding and flow stratification were observed under immiscible state. Miscible CO2 injection eliminated the influence of buoyancy, thereby expanding the area for CO2 storage and enhancing oil production. Non-uniform miscibility was observed during miscible CO2 injection, caused by connate water, tiny pores, and differential pressure. Small dispersed oil such as droplet oil and film oil remained in the water-flooded pores, resulting in strong Jamin effect, and thus increasing the oil production by inhibiting gas overriding and expanding CO2 sweeping area in WAG. However, water slugs occupied a large pore volume and drove out the CO2 stored previously, resulting in low CO2 storage. Different schemes were also evaluated using core flooding experiments. Miscible injection produced 20.5% and 2.9% more oil than immiscible CO2 injection and WAG, respectively. Besides, the produced gas by miscible CO2 injection was 46.5% and 47.6% lower than those of immiscible CO2 injection and WAG, respectively