Abstract
Abstract. Travertine deposits present above the St. Johns Dome natural CO2 reservoir in Arizona, USA, document a long (>400 kyr) history of surface leakage of CO2 from a subsurface reservoir. These deposits are concentrated along surface traces of faults, implying that there has been a structural control on the migration pathway of CO2-rich fluids. Here, we combine slip tendency and fracture stability to analyse the geomechanical stability of the reservoir-bounding Coyote Wash Fault for three different stress fields and two interpreted fault rock types to predict areas with high leakage risks. We find that these areas coincide with the travertine deposits on the surface, indicating that high-permeability pathways as a result of critically stressed fracture networks exist in both a fault damage zone and around a fault tip. We conclude that these structural features control leakage. Importantly, we find that even without in situ stress field data, the known leakage points can be predicted using geomechanical analyses, despite the unconstrained tectonic setting. Whilst acquiring high-quality stress field data for secure subsurface CO2 or energy storage remains critical, we shown that a first-order assessment of leakage risks during site selection can be made with limited stress field knowledge.
Highlights
The successful subsurface storage of fluids in sedimentary basins is key for geo-energy technologies such as Carbon Capture and Storage (CCS), cited as a cost-effective tool for climate change mitigation, or for energy storage, required to balance the intermittency of future energy systems relying on renewable sources (Alcalde et al, 2018; Matos et al, 2019; Scott et al, 2013)
The integrity of such engineered subsurface storage sites is controlled by a range of geological, geochemical and geotechnical factors
This so-called fault-valve behaviour, where faults act as highly permeable pathways for fluid discharge, is likely for faults that remain active while unfavourably oriented for reactivation within the prevailing stress field (Sibson, 1990)
Summary
The successful subsurface storage of fluids in sedimentary basins is key for geo-energy technologies such as Carbon Capture and Storage (CCS), cited as a cost-effective tool for climate change mitigation, or for energy storage, required to balance the intermittency of future energy systems relying on renewable sources (Alcalde et al, 2018; Matos et al, 2019; Scott et al, 2013). If fracture networks or faults are close to failure due to tectonically induced changes in the stress conditions or changes in pore pressure, vertical fluid flow is enhanced (Barton et al, 1995; Wiprut and Zoback, 2000) This so-called fault-valve behaviour, where faults act as highly permeable pathways for fluid discharge, is likely for faults that remain active while unfavourably oriented for reactivation within the prevailing stress field (Sibson, 1990). Geomechanical parameters such as slip tendency (Morris et al, 1996) or fracture stability (Handin et al, 1963; Terzaghi, 1923) can be used to assess the potential of vertical fluid flow. We show that leakage locations are controlled by the orientation of the reservoir bounding fault with respect to the regional stress field
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