Evaluation of CO2 injection in shale gas reservoirs with multi-component transport and geomechanical effects

- Shale gas models for CO2 injection considering multi-component transport and geomechanical effect is presented.
- In shale gas reservoir models, CO2 flooding and huff and puff techniques are performed.
- In Barnett shale model, CO2 injection is effective for improving CH4 production and CO2 storage.
- Critical factors for CO2 injection in shale gas reservoirs are analyzed.

Although research on CO2 injection in shale gas reservoirs has been focused for enhanced gas recovery (EGR) and CO2 storage, previous studies have not examined both multi-component transport and geomechanical effects. Therefore, this study presents new shale gas models for CO2 injection considering multi-component adsorption, dissolution, molecular diffusion, and stress-dependent compaction. Based on these mechanisms and data for Barnett shale field, a simulation model was constructed for CO2 flooding and huff and puff. The proposed model was used to examine the effects of CO2 injection to EGR and CO2 storage and various mechanisms. The results presented that CO2 flooding and huff and puff improve CH4 production by 24% and 6% respectively compared with no injection scenario. At the end of simulated time, the injected CO2 is stored as free, adsorbed, and dissolved states in proportions of 42%, 55%, and 3% respectively. To confirm these results, Marcellus and New Albany shale models, which have different reservoir properties, are generated and compared with Barnett shale model. However, in Marcellus and New Albany shale models, effects of CO2 injection are lower than that of Barnett shale model. Therefore, to investigate factors affecting to the efficiency of CO2 injection in shale gas reservoirs, extensive simulations were performed. Results of the simulation analyses show that natural fracture permeability, hydraulic fracture half-length, well spacing, and Langmuir constants are significant factors for EGR and CO2 storage. For the real applications, these parameters should be mainly considered. The investigations performed in this study present better understanding of CO2 injection processes to EGR and CO2 storage and they are important for optimizing the designs of CO2 injection in field applications.