Product Summary

Regional Subsurface Stress Assessment For CO₂ Storage in Candidate Basal Reservoirs in the PCOR Region

A screening-level regional evaluation of basement and mechanical overburden stress across the geologically diverse PCOR Partnership region was carried out by the Energy and Environmental Research Center (EERC). The main objective of the project was to assess potential for carbon dioxide (CO₂) storage in candidate basal reservoirs by characterizing the likelihood of basement fault reactivation technical uncertainties. Eight "stress focus areas" were identified across the PCOR study area based on elevated industry carbon capture and storage (CCS) activity, presence of basement faulting, and availability of subsurface stress and reservoir characterization data to carry out screening-level geomechanics analyses. Based on the availability of subsurface stress and reservoir characterization calibration. data, a deterministic and probabilistic critical stress analysis of published basement faults assuming storage of injected CO₂ in a basal reservoir was carried out in four of the eight stress focus areas using geomechanical and hydrological criteria and regional calibration data that were adapted for use in the modeling. Key conclusions include that faulting and fracturing associated with reactivated basement faults in tectonically active regions can occur in basal reservoirs, particularly the geomechanically stronger intervals, leading to a higher risk of fault slippage and related induced seismicity in response to fluid injection (CO₂, produced water disposal, fracture fluids, etc.). Thermally induced subsurface stress in response to CO₂ injection was not considered in this study because of the lack of calibration data and coupled flow modeling resources; however, it is generally agreed in the literature that lower-temperature CO₂ injected into a storage reservoir reduces fracture gradient, hence potentially reducing storage capacity. This is an active, developing, and complex area of research within industry and academia. Additionally, a scalable and integrated site-specific structural interpretation and geomechanics workflow to characterize and carry out a critical stress analysis of identified faults and associated fractures has been captured.