The current technique to produce shale oil is through primary depletion using horizontal wells with multiple transverse fractures. The oil recovery in oil-bearing shale reservoirs may be less than 10%, which leaves a large percentage of the oil unrecoverable without enhanced oil recovery methods. However, there is no EOR method tested or implemented in shale oil reservoirs. Before testing an EOR method, feasible methods need to be screened.
In this paper a screen study was first conducted to analyze the feasibility of every EOR method for a Wolfcamp shale oil reservoir. Actual reservoir and fluid data, and field operational parameters were used. The study shows that water injection and gas injection are most feasible EOR methods. After that, a detailed simulation study was carried out to evaluate the potentials of water and gas injection. The model was calibrated with the actual reservoir performance data. Waterflooding, cyclic water injection, gas flooding and cyclic gas injection were evaluated. The results show that cyclic gas injection provides the highest EOR potential for this reservoir. Simulation results indicate that the oil recovery factor can be increased more than one time by gas injection. This study provides a justification for a possible field implementation in the shale reservoir. It also provides a guide for the EOR screening in shale oil reservoirs.
Unconventional shale reservoirs are generally produced by stimulation techniques. A horizontal well with multiple transverse fractures has proven to be an effective technique for shale gas and shale oil production. However, shale oil production faces more challenges compared with shale gas production. Even applying multi-stage hydraulic fracturing techniques, the final oil recovery factors using existing methods are only a few percent. Oil rate and reservoir pressure drop very quickly. Because most of oil remains unrecoverable even using the expensive horizontal well drilling combined with hydraulic fracturing, seeking the ways to enhance oil recovery will be the continuous efforts.