Subparallel faults and horizontal-stress orientations: an evaluation of in-situ stresses inferred from elliptical wellbore enlargements

Abstract

Stress-induced wellbore-enlargement (breakout) data from the Marietta basin in south-central Oklahoma and the Bravo dome area of the central Texas Panhandle show a possible variation in the orientation of horizontal stress trajectories across areas bounded by subparallel faults. Regional studies of breakout and hydraulic fracturing-stress data indicate a northeast-southwest-oriented maximum principal horizontal stress ( SH max ) oriented oblique to westnorthwest-striking subparallel faults in these two study areas. Subtle variation in long-axis orientations of elliptically shaped wellbore enlargements from wells located between and near the ends of mapped subparallel faults in the Marietta basin and in the Bravo dome area indicates a possible local rotation of SH max . From the observed variation in the mean orientations of wellbore enlargements from selected wells, it is inferred that as much as 52° and 22° of stress trajectory rotation occurs between subparallel faults in the Marietta basin and the Bravo dome area, respectively. Assuming the areas bounded by these subparallel faults are functioning as stress field discontinuities, factors affecting local stress trajectory reorientation may include the amount of fault overlap, fault separation and differences in Young's modulus of the faulted rock units. Another factor contributing to or controlling suspected stress trajectory reorientation might be the influence of anisotropic rock-fabric properties.