Variations in the direction of the maximum horizontal compressive stress (SHmax) may significantly change the potential of faults to slip, especially if the SHmax orientation changes over relatively small distances. To estimate the potential for slip on mapped faults in the Delaware Basin where a regional, large (∼150°) SHmax clockwise rotation is observed from north to south, we adapted the Fault Slip Potential (FSP) code (freely available from the Stanford Center for Induced and Triggered Seismicity) to accommodate continuous variations of stress orientation. Using an interpolated and smooth stress field, the upgraded version of the software takes discrete stress orientation values sampled from the smoothed stress field at the center of each specific fault segment for probabilistically determination of fault slip potential. In addition, the new code makes it possible to estimate the slip potential with relation to changes in the relative magnitudes of the three principal stresses by using a discrete Aϕ parameter. We present an updated FSP map of the Delaware basin utilizing the continuous stress orientation map and newly identified basement-rooted faults in the basin. Both the new FSP analysis technique and re-mapping of the faults in the area indicates that the Grisham fault (one of the largest mapped faults in the basin) is less likely to slip in response to fluid pressure increases than previously believed. However, several other basement-rooted faults that are parallel to the SHmax direction may become a seismic hazard if there is deep water disposal in their vicinity.
Detailed knowledge of stress orientation and magnitude is of first-order importance when considering a fault slip potential and its seismic hazard. Stress orientation and magnitude can vary at scales ranging from tens of meters to hundreds of kilometers. In areas where the stress orientation changes over a short distance, it is difficult to predict potentially active (critically stressed) faults. Examples for short distance stress orientation change can be found in the updated North America State of Stress Map that includes areas such as the Raton Basin and the Delaware Basin (Lund Snee and Zoback, 2020). The maximum compression orientation in the Delaware Basin of West Texas and Southeast New Mexico varies from SN in the northern part of the Basin, from E-W in the central part of the basin, and NW-SE in the southern part of the basin (Dvory and Zoback, 2021). A geomechanical investigation and classification of faults with the optimal orientation for sliding was conducted by Lund Snee and Zoback (2018). Despite the rapid increase in the geomechanical understanding of state of stress in the Delaware Basin, it was only recently that substantial evidence of direct stress measurements and detailed fault mapping were added to the reservoir dataset (Lund Snee and Zoback, 2020; Dvory and Zoback, 2021; Hennings et al., in review). The newly acquired knowledge has enabled development of a new approach for Fault Slip Potential (FSP) analysis. In this approach, we rely on the high-resolution stress orientation measurements to construct a smoothed stress map and to define a discrete stress value for each fault segment in the updated faults catalogue.
