April 14, 2022 DGS Luncheon Presentation REMINDER- Lily Horne

Characterization and Tectonic Synthesis of the Greater Permian Basin: implications for fault mapping and hazard assessment in the Midland Basin

Elizabeth Horne, Center for Integrated Seismicity Research (CISR), Bureau of Economic Geology

Abstract:

The Midland Basin of West Texas is an important petroleum producing region that has experienced an increase in the rate and magnitude of seismicity, with 38 ≥ 3.0 Mw events between 2019-2021. Earthquakes have occurred in spatiotemporally isolated clusters and are linked to oilfield practices, including the disposal of wastewater (SWD) and hydraulic fracturing. Specifically, SWD into deep and shallow formations have increased from 2015-2021 and many of the recent earthquake sequences are spatiotemporally coincident with horizontal drilling locations. To understand the causal factors of earthquakes in the region and assess the evolving hazard, we present a new in-progress semi-regional fault interpretation and the results of carrying out a Fault Slip Potential (FSP) analysis.

There are three orders of deformation observed in the Midland Basin. These include 1^st order, basement-rooted regional faults, which define the boundary between the Midland Basin and Central Basin Platform. 2^nd order structures include basement-rooted, local, fault-bounded uplifts and fault related folding. 3^rd order structures are interpreted to be segmented, parallel trending, high-angle fault zones, which locally accommodated strike-slip motion. Within each hierarchal group, faults are characterized by trend and structural style, as well as vertical extent. 1^st and 2^nd order faults are basement-rooted high-angle (~65 ± 5°) reverse faults that trend NNW-SSE and accommodated primarily dip-slip motion. 3^rd order fault segments are steeply dipping (~80 ± 10°) and trend WNW-ESE and WSW-ENE. These faults are interpreted to have locally accommodated left and right lateral strike-slip movement, and subordinate (NE-SW) normal and reverse dip-slip, right lateral strike-slipping faults formed in locations of competing strike-slip faults. Additionally, these segments formed kinematic linkages between 1^st and 2^nd-order fault zones. Deformation along first order structures remained active through the early Wolfcampian, with syntectonic deposition through the Wolfcamp D. 2^nd order and 3^rd order fault zones may have remained active, but observable dip-slip motion dissipates after Strawn deposition. Karst in Paleozoic strata accompanies 3^rd order fault and fractures zones. FSP results show that 3^rd order faults are sensitive to reactivation under modest increases in pore pressure. Karst may have a profound impact in hydraulic connectivity along sensitive 3^rd order fault corridors.

Elizabeth A. Horne (Lily) is a structural geologist at the Bureau of Economic Geology, UT Austin. She has a geology M.S. from Colorado School of Mines and a geology B.S. from Utah State University. Her research interests include integrating field and subsurface datasets to generate three-dimensional (3-D) fault models that can be used to better understand the kinematic evolution of various structural systems, as well as determine mechanisms for modern seismicity, both natural and induced.