Complex Shear-Wave Anisotropy from Induced Earthquakes in West Texas

2020 ◽  
Vol 110 (5) ◽  
pp. 2242-2251 ◽  
Author(s):  
Regan Robinson ◽  
Aibing Li ◽  
Alexandros Savvaidis ◽  
Hongru Hu
Keyword(s):  
Shear Wave ◽  
Induced Seismicity ◽  
High Rate ◽  
Normal Faults ◽  
Permian Basin ◽  
Induced Earthquakes ◽  
Large Delay ◽  
Delaware Basin ◽  
West Texas ◽  
Shallow Earthquakes

ABSTRACT We have analyzed shear-wave splitting (SWS) data from local earthquakes in the Permian basin in west Texas to understand crustal stress change and induced seismicity. Two SWS parameters, the fast polarization direction and the delay time, are computed using a semiautomatic algorithm. Most measurements are determined in the Delaware basin and the Snyder area. In both regions, SWS fast directions are mostly consistent with local SHmax at stations that are relatively far from the earthquake clusters. Varying fast directions at one station are related to different ray paths and are probably caused by heterogeneity. In the Snyder area, most northeast–southwest fast directions are from the events in the northern part of the cluster, whereas the northwest–southeast fast directions are mostly from the southern part. The northeast–southwest and northwest–southeast fast directions could be attributed to the northeast-trending normal faults and the northwest-trending strike-slip faults, respectively. SWS results in the Delaware basin have two unique features. First, most shallow earthquakes less than 4 km deep produce relatively large delay times. This observation implies that the upper crust of the Delaware basin is highly fractured, as indicated by the increasing number of induced earthquakes. Second, diverse fast directions are observed at the stations in the high-seismicity region, likely caused by the presence of multiple sets of cracks with different orientations. This situation is possible in the crust with high pore pressure, which is expected in the Delaware basin due to extensive wastewater injection and hydraulic fracturing. We propose that the diversity of SWS fast directions could be a typical phenomenon in regions with a high rate of induced seismicity.

Short-Term Probabilistic Hazard Assessment in Regions of Induced Seismicity

2020 ◽  
Vol 110 (5) ◽  
pp. 2441-2453 ◽  
Author(s):  
Ganyu Teng ◽  
Jack W. Baker
Keyword(s):  
Hydraulic Fracturing ◽  
Induced Seismicity ◽  
Aftershock Sequence ◽  
Earthquake Occurrence ◽  
Induced Earthquakes ◽  
Short Term ◽  
Wastewater Disposal ◽  
West Texas ◽  
Hazard Level ◽  
Natural Earthquakes

ABSTRACT This project introduces short-term hazard assessment frameworks for regions with induced seismicity. The short-term hazard is the hazard induced during the injection for hydraulic-fracturing-induced earthquakes. For wastewater-disposal-induced earthquakes, it is the hazard within a few days after an observed earthquake. In West Texas, hydraulic-fracturing-induced earthquakes cluster around the injection activities, and the earthquake occurrence varies greatly in time and space. We develop a method to estimate the hazard level at the production site during the injection, based on past injection and earthquake records. The results suggest that the injection volume has a negligible effect on short-term earthquake occurrence in this case, because injection volumes per well fall within a relatively narrow range, whereas the regional variations in seismic productivity of wells and b-values are important. The framework could be easily modified for implementation in other regions with hydraulic-fracturing-induced earthquakes. We then compare the framework with wastewater-disposal-induced earthquakes in Oklahoma–Kansas and natural earthquakes in California. We found that drivers of short-term seismic hazard differ for the three cases. In West Texas, clustered earthquakes dominate seismic hazards near production sites. However, for Oklahoma–Kansas and California, the short-term earthquake occurrence after an observed mainshock could be well described by the mainshock–aftershock sequence. For Stillwater in Oklahoma, aftershocks contribute less to the hazard than San Francisco in California, due to the high Poissonian mainshock rate. For the rate of exceeding a modified Mercalli intensity of 3 within 7 days after an M 4 earthquake, the aftershock sequence from natural earthquakes contributed 85% of the hazard level, whereas the aftershock contribution was only 60% for induced earthquakes in Oklahoma. Although different models were implemented for hazard calculations in regions with hydraulic fracturing versus wastewater injection, injection activities could be drivers of short-term hazard in both cases.

scholarly journals Stability of the Fault Systems That Host-Induced Earthquakes in the Delaware Basin of West Texas and Southeast New Mexico

2021 ◽  
Vol 1 (2) ◽  
pp. 96-106
Author(s):  
Peter Hennings ◽  
Noam Dvory ◽  
Elizabeth Horne ◽  
Peng Li ◽  
Alexandros Savvaidis ◽  
...  
Keyword(s):  
New Mexico ◽  
Natural State ◽  
Fault Rupture ◽  
Induced Earthquakes ◽  
Delaware Basin ◽  
West Texas ◽  
Geomechanical State ◽  
Earthquake Zone ◽  
Earthquake Sequences

Abstract The Delaware basin of west Texas and southeast New Mexico has experienced elevated earthquake rates linked spatiotemporally to unconventional petroleum operations. Limited knowledge of subsurface faults, the in situ geomechanical state, and the exact way in which petroleum operations have affected pore pressure (Pp) and stress state at depth makes causative assessment difficult, and the actions required for mitigation uncertain. To advance both goals, we integrate comprehensive regional fault interpretations, deterministic fault-slip potential (DFSP), and multiple earthquake catalogs to assess specifically how faults of two systems—deeper basement-rooted (BR) and shallow normal (SN)—can be made to slip as Pp is elevated. In their natural state, the overall population faults in both the systems have relatively stable DFSP, which explains the low earthquake rate prior to human inducement. BR faults with naturally unstable DFSP and associated earthquake sequences are few but include the Culberson–Mentone earthquake zone, which is near areas of wastewater injection into strata above basement. As a system, the SN faults in the southcentral Delaware basin are uniformly susceptible to slip with small increases in Pp. Many earthquakes sequences have occurred along these shallow faults in association with elevated Pp from shallow wastewater injection and hydraulic fracturing. Our new maps and methods can be used to better plan and regulate petroleum operations to avoid fault rupture.

scholarly journals Widespread deep seismicity in the Delaware Basin, Texas, is mainly driven by shallow wastewater injection

2021 ◽  
Vol 118 (20) ◽  
pp. e2102338118
Author(s):  
Guang Zhai ◽  
Manoochehr Shirzaei ◽  
Michael Manga
Keyword(s):  
Induced Seismicity ◽  
The United States ◽  
Plate Boundaries ◽  
Induced Earthquakes ◽  
Wastewater Disposal ◽  
Delaware Basin ◽  
The North ◽  
Hydrogeological Parameters ◽  
Stress Changes ◽  
Deep Seismicity

Industrial activity away from plate boundaries can induce earthquakes and has evolved into a global issue. Much of the induced seismicity in the United States' midcontinent is attributed to a direct pressure increase from deep wastewater disposal. This mechanism is not applicable where deep basement faults are hydraulically isolated from shallow injection aquifers, leading to a debate about the mechanisms for induced seismicity. Here, we compile industrial, seismic, geodetic, and geological data within the Delaware Basin, western Texas, and calculate stress and pressure changes at seismogenic depth using a coupled poroelastic model. We show that the widespread deep seismicity is mainly driven by shallow wastewater injection through the transmission of poroelastic stresses assuming that unfractured shales are hydraulic barriers over decadal time scales. A zone of seismic quiescence to the north, where injection-induced stress changes would promote seismicity, suggests a regional tectonic control on the occurrence of induced earthquakes. Comparing the poroelastic responses from injection and extraction operations, we find that the basement stress is most sensitive to shallow reservoir hydrogeological parameters, particularly hydraulic diffusivity. These results demonstrate that intraplate seismicity can be caused by shallow human activities that poroelastically perturb stresses at hydraulically isolated seismogenic depths, with impacts on seismicity that are preconditioned by regional tectonics.

Sign in / Sign up

Export Citation Format

Share Document