Thermo‐poroelastic responses of a pressure‐driven fracture in a carbon storage reservoir and the implications for injectivity and caprock integrity

• Published in: International journal for numerical and analytical methods in geomechanics 2021-04, Vol.45 (6), p.719-737
• Main Authors: Fu, Pengcheng, Ju, Xin, Huang, Jixiang, Settgast, Randolph R., Liu, Fang, Morris, Joseph P.
• Format: Article
• Language: English
• Subjects: caprock integrity; Carbon capture and storage; Carbon dioxide; Carbon sequestration; Computational fluid dynamics; Contraction; Cooling; Crack propagation; Fluids; Fracture mechanics; geological carbon storage; Heat transport; hydraulic fracture; Injection; Integrity; Mechanics; Multiphase flow; Permeability; Poroelasticity; Pressure; Reservoir storage; Reservoirs; Rocks; Storage reservoirs; supercritical CO2; Thermal contraction; thermo‐hydro‐mechanical coupling
• ISSN: 0363-9061; 1096-9853
• DOI: 10.1002/nag.3165

CO2 injection into a reservoir with marginal permeability (≲ 10−14 m2) could induce pressure high enough to fracture the reservoir rock and/or caprock. A pressure‐driven fracture can immensely enhance the injectivity and would not compromise the integrity of the overall storage complex as long as the fracture is contained vertically. Conventional models for geologic carbon storage simply treat fractures as high‐permeability conduits, ignoring coupled interactions between the fluids, the fracture, the reservoir, and caprock. We employ a high‐fidelity model coupling multiphase flow, heat transport, poroelasticity, thermal contraction, as well as fracture mechanics to study thermo‐poroelastic responses of a pressure‐driven fracture in a carbon storage reservoir. We found that poroelasticity dictates that to maintain an open fracture in the reservoir rock requires a continuous and significant increase of pressure, potentially exceeding the fracturing pressure for the caprock. A closed‐form equation is derived to conservatively compute the pressure increase. Although cooling in the near‐well region could reduce the fracture‐opening pressure, the fracture propagation pressure is still dictated by processes in the far‐field rock unaffected by the cooling. This discrepancy causes a high net pressure near the injection well and could further drive the fracture into the caprock. However, while such fracturing is likely, we demonstrate that in many instances we can expect it to be contained.