Integrative Modeling of CO2 Injection for Enhancing Hydrocarbon Recovery and CO2 Storage in Shale Reservoirs

Abstract

Although research on CO2 injection in shale reservoirs has received significant interest recently, previous studies have not reflected the combined effects of characteristic mechanisms in shale reservoirs during CO2 injection. Stress-dependent compaction, multilayer adsorption, confinement effects, and molecular diffusion have been incorporated to simulate shale reservoirs accurately. Stress-dependent correlation was coupled with swelling and shrinkage by adsorption and desorption and confinement effects are considered by critical point shift correlation. From history matching based on the coupled mechanisms, field-scale reservoir models were developed for Barnett and Marcellus shale gas and East Texas shale oil reservoirs. In case of Barnett shale reservoir, results of history matching show that model with power law correlation corresponds with results of rate transient analysis. Marcellus shale reservoir model shows higher coefficient of power law correlation than Barnett shale reservoir due to high clay content. East Texas shale oil reservoir presents the importance of stress-dependent compaction and confinement effects. After history matching, numerical simulations of CO2 injection were run in the best matched models. In the suggested Barnett shale gas and Bakken shale oil reservoirs, CO2 injection provides positive effects on both hydrocarbon recovery and CO2 storage. Competitive adsorption between CO2 and CH4, molecular diffusion and stress-dependent compaction are of importance during CO2 injection. In both Barnett shale gas and Bakken shale oil models, CO2 flooding process is more effective for both hydrocarbon production improvement and CO2 storage than CO2 huff and puff process. Results of sensitivity analysis presented that information of fracture system such as conductivity of natural fracture and hydraulic fracture half-length is significantly important for successful CO2 injection in shale reservoirs. From extensive numerical simulations, this work provides a quantitative assessment on the potential of CO2 injection for both enhanced hydrocarbon recovery and CO2 storage and presents a better understanding of the major parameters affecting the effectiveness of CO2 injection process.