Slip tendency on cryptic faults in the Patterson Storage Site, a proposed CO2 repository in SW Kansas: Quantifying potential injection-induced seismicity hazards

The Patterson Storage Site is a proposed carbon capture and storage repository forming part of the North Hugoton Storage Complex (NHSC) in the Hugoton Gas Field in southwestern Kansas. This site is located on a 93 km² structural trend that is characterized by elevated well (formation) tops for Mississippian and deeper strata that define an NNW fault-dependent fold (closure). Recent increases in seismicity in Kansas and Oklahoma attributed to waste fluid injection have highlighted the need for mapping and geomechanical analysis of faults prior to full-scale injection operations. In order to assess the susceptibility of the Patterson site and NHSC for seismicity associated with hypothetical commercial-scale (50+ MMT) CO₂ injection and storage, we performed an initial assessment of structural lineaments, mapped from well-tops-based structure contour maps, as well as stress orientation and magnitude analysis to inform the slip tendency of mapped structures. A total of ~10 lineaments were identified within the Mississippian across the NHSC, with additional lineaments visible in stratigraphically higher (shallower) strata. In situ stresses across the NHSC were determined from two wells with drilling-induced fractures and two wells with borehole breakouts. Drilling-induced fractures (n=6 and n=80) suggest that the maximum horizontal stress (SH_max) is oriented ENE-WSW, consistent with readings elsewhere in the state. Borehole breakouts (n=19 and n=1) indicated that the minimum horizontal stress (Sh_min) is oriented SSE-NNW. To define reservoir and stress gradients, we use pressure data from three wells and density logs from ~200 wells in the study area. The stress orientations and magnitudes are used to quantify the slip tendency (τ/σ_n) of the mapped lineaments across the NHSC. Slip tendency results vary with azimuth, with the majority of lineaments in a stable state (slip tendency < 0.5); however, a few are in a critical state. Newly acquired 3D seismic reflection data for the Patterson Storage Site and legacy datasets will allow us to further map and model faults within the site and better assess their potential for reactivation with fluid injection (brine or CO₂).