Abstract
AbstractAn increase in injection activity associated with energy production in southern Kansas starting in 2013 has been linked to the occurrence of more than 130,000 earthquakes (M −1.5 to 4.9) between 2014 and 2017. Studies suggest that the dramatic increase in seismicity rate is related to wastewater injection into the highly permeable Arbuckle formation. Most of the seismicity is located in the underlying crystalline basement, for which hydrological properties and specific fault geometries are unknown. Additionally, some earthquake clusters occurred relatively far (tens of kilometers) from the main injection wells. Therefore, the effect of pore pressure diffusion may be insufficient to explain the relation between the volume of injected fluids and the spatiotemporal evolution of seismicity. Combining physical models (static stress and poroelasticity) and a statistical cluster analysis applied to a high‐resolution relocated catalog, we analyze the evolution of seismicity in southern Kansas. We find that pore pressure changes (Δp) and Coulomb stress changes (ΔCFS) due to fluid diffusion smaller than 0.1 MPa are enough to initiate seismic sequences, which then evolve depending on their distance from the major injection wells. However, we find that earthquake sequences have different seismogenic responses to Δp and ΔCFS in terms of triggering threshold. In regions located close to disposal wells (Harper area) our cluster analysis suggests that both earthquake interactions and fluid diffusion control the evolution of seismicity. On the other hand, at greater distances (Milan area), where clustering behavior suggests greater earthquake interactions, we find that coseismic ΔCFS are larger than Δp.
Highlights
Pore fluid pressure increase and poroelastic stresses resulting from wastewater disposal are responsible for the sharp increase in seismicity in Oklahoma and southern Kansas over the past 6 years (Keranen et al, 2014; Langenbruch et al, 2018; Peterie et al, 2018; Rubinstein et al, 2018; Weingarten et al, 2015; Zhai et al, 2019, 2020)
We find that pore pressure changes (Δp) and Coulomb stress changes (ΔCFS) due to fluid diffusion smaller than 0.1 MPa are enough to initiate seismic sequences, which evolve depending on their distance from the major injection wells
We use the finite element software Comsol Multiphysics® following the linear poroelasticity theory (Biot, 1941) to simulate the coupled relation between pore pressure and solid matrix stress changes induced by wastewater injection in the Arbuckle formation from 102 Class II disposal wells located in southern Kansas and northern Oklahoma (Figure 1), which operated from January 2012 to December 2016
Summary
Pore fluid pressure increase and poroelastic stresses resulting from wastewater disposal are responsible for the sharp increase in seismicity in Oklahoma and southern Kansas over the past 6 years (Keranen et al, 2014; Langenbruch et al, 2018; Peterie et al, 2018; Rubinstein et al, 2018; Weingarten et al, 2015; Zhai et al, 2019, 2020). Atop the Arbuckle Group is the Ordovician-Mississippian shale layer, which acts as a seal (Carr et al, 1986). Both the Arbuckle Group and the Precambrian basement are thought to be highly fractured. In addition to pore pressure changes and poroelastic stresses, studies have invoked static Coulomb failure stress changes (ΔCFS) due to moderate (M ≥ 3) injection-induced foreshocks as possible triggering sources for the M5.7 Prague (Sumy et al, 2014) and the M5.8 Pawnee (Chen et al, 2017) earthquakes that both occurred in Oklahoma. Studies have suggested the important role of earthquake-earthquake interactions in several cases of seismicity induced by hydraulic fracturing (Kettlety et al, 2019; Peña Castro et al, 2020) and geothermal enhancement (Catalli et al, 2016)
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