DETERMINING THE RISK FOR INDUCED SEISMICITY ASSOCIATED WITH PILOT-SCALE CO2 INJECTION AT WELLINGTON FIELD, SUMNER COUNTY, KANSAS

Wellington Field in north-central Sumner County, Kansas is the site of two planned CO₂ injection tests focused on evaluating the potential of Mississippian reservoirs for CO₂-enhanced oil recovery and the CO₂ storage potential of the Cambro-Ordovician Arbuckle Group saline aquifer. However, unprecedented seismicity west of the field and across the region has raised concerns about the role of fluid injection (CO₂ or brine) in fault reactivation. This project focuses on the potential effects of CO₂ injection on subsurface faults during these planned injection tests. Our approach is to (1) map faults using 3D seismic reflection data, (2) determine in-situ stress orientations using image logs and focal mechanism inversion, (3) estimate in-situ stress magnitudes using well test data, density logs, and derivative methods, and (4) predict if mapped faults are prone to reactivation through slip and dilation tendency analysis. 3D seismic data reveal 60 near vertical faults with strikes ranging from 0°-43°, lengths from 140-410 m, and vertical separations of 3-32 m. Drilling-induced tensile fractures (N=78) identified from image logs and inversion of earthquake focal mechanism solutions (N=54) are consistent with the maximum horizontal stress (SHmax) oriented ~E-W. Both strike-slip and normal-slip fault plane solutions for earthquakes near the study area suggest that SHmax and Sv (vertical stress) may be similar in magnitude, consistent with estimated stress gradients for Sv (0.023-0.024MPa/m), SHmax (0.02-0.031MPa/m), and Shmin (minimum horizontal stress; 0.012MPa/m). Preliminary slip and dilation tendency analysis suggests that faults with strikes of 0°-20° are stable, whereas faults with strikes of 26°-44° may have a moderate risk for reactivation with increasing pore-fluid pressure. Additional work will be done to evaluate the magnitude of pore fluid pressure change required to trigger slip, different injection scenarios, and how the mapped faults behave at depth.