Evaluation of the EOR potential of gas and water injection in shale oil reservoirs

• Evaluated EOR potentials of gas and waterflooding in shale oil reservoirs.
• It is shown that gas injection is preferred method to water injection because of higher pressure gradient and lower injectivity of waterflooding.
• It is shown that one of the important mechanisms of gas and waterflooding is pressure maintenance.

With the relatively modest natural gas price, producing oil from unconventional shale reservoirs has attracted more and more interest from oil operators. Although many tremendous efforts have been made to develop shale resources, the ultimate oil recovery is still low (5–10%). Because of the important role of shale resources in the future oil and gas industry, more stimulation and production strategies are being considered and tested to find ways to improve oil production from shale reservoirs. Before applying a specific method to enhance oil recovery (EOR) in the field or conducting a research in laboratory, the simulation approach is a cheap and fast approach to evaluate its EOR potential. The analysis of simulation results will be helpful in designing laboratory experiments and field testing.In this paper we use a simulation approach to evaluate the EOR potential in shale oil reservoirs by gas flooding and waterflooding. Production behavior and oil recovery of different schemes are discussed through sensitivity studies. Simulation results of primary production, gas injection and water injection are compared. Results show that miscible gas injection has a higher potential to improve oil recovery from shale oil reservoirs than water injection. Gas injection above a minimum miscible pressure (MMP) can be fully miscible with oil, thus reducing oil viscosity significantly, in addition to the mechanism of pressure maintenance. Simulation results indicate that the oil recovery factor can be increased up to 15.1% by gas injection in a hydraulically fractured shale reservoir, whereas the oil recovery factor from the primary depletion is only 6.5%. The oil recovery from waterflooding is about 11.9% which is lower than that from gas flooding. The results indicate that miscible gas flooding could be a way to enhance oil recovery in shale oil reservoirs.