Improving oil recovery from shale oil reservoirs using cyclic cold carbon dioxide injection - An experimental study

In this study, effects of injecting gas temperature and pressure on oil recovery factor (RF) of shale oil reservoirs were investigated by implementing cyclic cold carbon dioxide (CO2) injection on Eagle Ford Shale Oil core samples. Also, effects of injecting gas temperature on porosity, permeability, and brittleness indices of these core samples were assessed. An experimental setup was designed and built to implement CO2 cyclic gas injection and thermal shock tests. Four Eagle Ford Shale outcrop core samples were used in this study. The saturated samples were heated to 180 degrees F and carbon dioxide at various combinations of pressure (1000 psi, 2000 psi, 3000 psi, and 4000 psi) and temperature (-15 degrees F, 0 degrees F, 32 degrees F, and 74 degrees F) was injected into them. Oil RF for each experiment was measured after five days of production period. Additionally, porosity, permeability and ultrasonic velocity of each core sample were measured both prior to and after conducting the experiment. The results indicate that injecting CO2 at low temperature results in higher oil recovery factor (up to 7%) than injecting carbon dioxide at ambient temperature. It was also observed that injecting cold CO2 enhanced both porosities and permeabilities of the core samples. The porosities and the permeabilities of the core samples enhanced by up to 3.5% and 8.8%, respectively. Also, a noticeable reduction (between 100 ft/s and 400 ft/s) in P-wave velocity was observed after injecting the cold gas into the core samples, which is an indication of creating induced fractures. The results also revealed that injecting the cold gas increased the brittleness indices of the core samples by up to 8. Hence, cyclic cold carbon dioxide injection could be potentially implemented in the shale oil fields to improve the efficiency of the current industry practice of cyclic gas injection technique.