Carbon Dioxide Injection Pressure and Reservoir Temperature Impact on Oil Recovery from Unconventional Shale Reservoirs During Cyclic CO₂ Injection: An Experimental Study

Carbon dioxide (CO₂) injection has recently been applied in unconventional shale reservoirs to increase oil recovery. There are many methods by which CO₂ can be injected. One of the most common methods, especially in unconventional reservoirs, is cyclic CO₂ injection. This research experimentally investigates the ability of cyclic CO₂ injection to increase oil recovery from unconventional shale reservoir, and the impact of reservoir thermodynamics, including pressure and temperature, on the oil recovery potential. The experiments were conducted using a specially designed vessel to mimic the cyclic CO₂ injection operation. The shale cores were saturated with crude oil for seven consecutive months at high temperature. The cores were then placed in the huff-n-puff vessel and the experiment was commenced. The pressure and temperature conditions were found to have a strong impact on oil recovery, especially as the injection cycles progressed. The thermodynamic conditions were also found to impact the core integrity greatly, with some cores breaking at some conditions, and the natural fractures being stimulated as well. This research can help illustrate the impact of reservoir thermodynamics on the oil recovery potential from unconventional shale reservoirs during cyclic CO₂ injection.