Collaborative Research: Coupled flow-geomechanical models applied to assess earthquake triggering in tectonically active regions – The Los Angeles basin, CA

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Induced seismicity, or earthquakes caused by human activities, are a growing societal concern affecting hydrocarbon and geothermal energy production, gas storage, and subsurface carbon sequestration efforts in the Unites States and throughout the world. Distinguishing between tectonic and induced earthquakes is generally straightforward in areas with little or no natural seismicity. In tectonically active regions, however, discriminating between natural and induced seismicity is far more challenging, particularly as the latter may only be detected by changes in the size, frequency, or geographic distribution of earthquakes over time. Moreover, induced seismicity in these regions poses great risks, as human activities may trigger larger and more destructive earthquakes. This study develops state-of-the-art, physics-based models to investigate how nearly a century of production and waste-water injection in hydrocarbon fields of the Los Angeles basin, California, have impacted the stability of faults in the area. These models will consider stress changes on faults caused both by tectonic and anthropogenic processes, thus helping to distinguish between tectonic and induced events. This study will advance methodologies to investigate and manage triggered seismicity in Los Angeles and other tectonically active regions, as well as address the growing concerns about induced seismicity in a tectonically active region with a population of nearly 20 million people.This project develops coupled geomechanical and multiphase fluid flow models to assess the impact of hydrocarbon production and wastewater reinjection in petroleum fields over the past century on seismic activity in the Los Angeles basin, CA. To describe the mechanical and hydraulic behavior of faults, and the influence of the change in pressure as well as full stress tensor on fault slip, this project will employ advanced techniques for modeling coupled flow and geomechanics in faulted reservoirs with a rigorous formulation of nonlinear multiphase geomechanics. These simulations will be performed in detailed models of reservoirs embedded in regional descriptions of the tectonically active fault systems in the basin. The Los Angeles basin serves as an excellent laboratory to study triggered seismicity because of its extensive field operations, wealth of fault and reservoir data, and history of induced seismicity and ground surface subsidence. We will begin the study with the Wilmington field, which has produced more that 2.5 billion barrels of oil causing up to 9 meters of ground subsidence. The researchers have gathered the complete production and injection schedules (1936-2020) for more than 5000 wells to calibrate their models with reservoir pressure and measurements of ground surface deformation. Simulations will then be expanded to the basin scale, assessing how field operations have influenced seismicity on more than 20 active strike-slip and thrust fault systems. This will include detailed analysis of seismicity patterns, including those recorded by machine learning-enabled catalogs, as well as focus on large events (e.g., 1933 Long Beach M 6.3) that occurred in the vicinity of fields. The goal is to gain an improved understanding of triggered seismicity, along with more capable modeling tools, that can be used to manage subsurface energy operations in ways that minimize seismic hazard.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.