High density oilfield wastewater disposal causes deeper, stronger, and more persistent earthquakes

Abstract

Oilfield wastewater disposal causes fluid pressure transients that induce earthquakes. Here we show that, in addition to pressure transients related to pumping, there are pressure transients caused by density differences between the wastewater and host rock fluids. In northern Oklahoma, this effect caused earthquakes to migrate downward at ~0.5 km per year during a period of high-rate injections. Following substantial injection rate reductions, the downward earthquake migration rate slowed to ~0.1 km per year. Our model of this scenario shows that the density-driven pressure front migrates downward at comparable rates. This effect may locally increase fluid pressure below injection wells for 10+ years after substantial injection rate reductions. We also show that in north-central Oklahoma the relative proportion of high-magnitude earthquakes increases at 8+ km depth. Thus, our study implies that, following injection rate reductions, the frequency of high-magnitude earthquakes may decay more slowly than the overall earthquake rate.

Explications des pressions de fluides transitoires à longue portée engendrées par le stockage d’eaux usées de champs pétrolifères à l’aide du principe de superposition hydrogéologique

“…Kansas (Pollyea et al, 2019). The simulation results presented here further indicate that the principle of superposition explains how these residual pressure fronts merge to produce a region of elevated fluid pressure that systematically deepens even after injection operations cease (Fig 4d-f).…”

“…In closing, the hypothetical models developed for this study comprise idealized geology that neglects detailed fault structures and hydro-mechanical couplings that are known to influence earthquake triggering processes. Nevertheless, this study does account for several hydrogeological phenomenon that are now known to be critically important to fluid pressure accumulation and recovery, specifically thermal effects on fluid flow and variable fluid composition between wastewater and host rock (Pollyea et al, 2019). As a result, this modeling study provides the hydrogeological basis to apply the principle of superposition as a framework to understand and deconvolve complex interactions between pressure transients when numerous wastewater injection wells operate in close spatial proximity.…”

“…To understand the hydrogeology of long-range pressure transients during oilfield wastewater disposal, this study models several hypothetical wastewater injection scenarios using characteristics of the Anadarko Shelf geologic province of north-central Oklahoma. Between 2011 and 2015, this region experienced rapid increases in both oilfield wastewater disposal and earthquake occurrence (Pollyea et al, 2019;Pollyea et al, 2018b). The primary target reservoir for oilfield wastewater disposal is the Arbuckle formation, which is in direct hydraulic communication with the underlying Precambrian basement (Johnson, 1991 (Fig.…”

“…All model scenarios simulate 10 years of oilfield wastewater disposal followed by 10 years of post-injection fluid pressure recovery. These models also account for variable fluid composition, which has been shown to drive fluid pressure transients deeper into the seismogenic zone even after injection operations cease (Pollyea et al, 2019). The wastewater is representative of brine produced from the Mississippi Lime formation, which is reported to have a mean total dissolved solids (TDS) concentration of 207,000 ppm (Blondes et al, 2017).…”

Experimental measurements and modelling of viscosity and density of calcium and potassium chlorides ternary solutions

“…The calculated values were inserted into Eqs. (14) to (16) in order to predict the viscosity of ternary mixtures. Validity of GF model against KCl + CaCl 2 + H 2 O viscosity data was investigated by calculating AAD.…”