Stress perturbations associated with active faults penetrated by boreholes: Possible evidence for near‐complete stress drop and a new technique for stress magnitude measurement

Abstract

Detailed studies of stress-induced wellbore breakouts in wells drilled through active faults reveal stress field discontinuities that are apparently associated with recent fault movements. These discontinuities are expressed as localized rotations in wellbore breakout orientation in the vicinity of the fault penetrated by the borehole. This phenomenon is observed in a variety of tectonic environments and rock types. Utilizing cases where relatively complete knowledge of the horizontal principal stresses is available from in situ measurements, we use three-dimensional dislocation modeling to demonstrate that these discontinuities can be explained as the superposition of a reference stress state and a perturbation caused by movement on preexisting faults. Case studies from normal, strike-slip and reverse faulting stress states indicate that nearly complete stress drop is required to match the observed breakout orientation anomalies. Hydraulic fracturing data independently confirm the occurrence of nearcomplete stress drop on some faults penetrated by drilling. Modeling of the observed interactions between breakouts and fractures can also be used to obtain information about the magnitude of in situ stress. ! ' I BARTON AND ZOBACK: STRESS PERTURBATIONS AT ACTIVE FAULTS 9375 AND ZOBACK: STRESS PERTURBATIONS AT ACTIVE FAULTS 9383 ods, lnt. J. Rock Mech. Min. $ci. Geomech. Abstr., 26(6), 461-469, 1989. Baumgfirtner, J., F. Rummel, and M.D. Zoback, Hydraulic fracturing in situ stress measurements to 3 km depth in the KTB pilot hole VB, KTB Rep. 90-6a, edited by K. Bram, J. K. Draxler, W. Kessels, and G. Zoth, Niedersfichsisches Landesamt far Bodenforschung, Hannover, 1990.

IODP Expedition 319, NanTroSEIZE Stage 2: First IODP Riser Drilling Operations and Observatory Installation Towards Understanding Subduction Zone Seismogenesis

“…This orientation is similar to that measured at other sites across the prism during NanTroSEIZE Stage 1 and similar to the orientation at Site C0009 in the central forearc basin. An abrupt downhole change in breakout orientation across the megasplay fault zone at Site C0010 is consistent with a sharp mechanical discontinuity at the fault zone (Barton and Zoback, 1994); such a change is not observed at nearby Site C0004, where the megasplay is defined as a broad ~50-m-thick fault-bounded package. Minor faults are concentrated around the thrust zone, as might be expected.…”

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“…F7). A sharp discontinuity in stress orientation occurs across the base of the thrust wedge and is consistent with a fault discontinuity (Barton and Zoback, 1994). In contrast, the trend of breakouts at Site C0004 changes gradually downhole and is continuous across the base of the wedge (Kinoshita et al, 2008).…”

How faults wake up: The Guthrie-Langston, Oklahoma earthquakes

“…However, stress rotations of 20° or more are frequently observed locally in borehole data. Such rotations can be explained by slip on faults and reflect the heterogeneity of the state of stress (Barton and Zoback, 1994;Sahara et al, 2014;Schoenball and Davatzes, 2017).…”