Long‐period long‐duration seismic events during hydraulic fracturing: Implications for tensile fracture development

Abstract

Long‐period long‐duration (LPLD) seismic events are observed from a microseismic data set acquired by surface receivers in the Eagle Ford Shale. These events are characterized by low frequencies of 10–60 Hz and long durations of 30–60 s. The seismograms are dominated with P waves, and the frequency spectra have peaks at several isolated frequencies, similar to volcanic tremors. The LPLD events are located close to the horizontal hydraulic treatment well and migrate away from the well with time. These observations suggest that the LPLD events are related to hydraulic fracturing and are possibly caused by the jerky opening and resonance of fluid‐filled cracks. Imaging this type of LPLD events can potentially map fluid flow and tensile fracture development during hydraulic fracturing.

Long‐Period Long‐Duration Events Detected by the IRIS Community Wavefield Demonstration Experiment in Oklahoma: Tremor or Train Signals?

“…For example, the duration of our detected LPLD events is more than 300 s, much longer than the typical duration of 30-60 s for the LPLDs in the other studies. Furthermore, whereas the dominant frequency of our LPLD events is less than 10 Hz, the LPLD events during hydraulic fracturing can reach up to 60-100 Hz (Das and Zoback, 2013a,b;Hu et al, 2017;Chen et al, 2018). These differences suggest that the source mechanisms of LPLD events observed in this study are different from recent observations near hydraulic fracturing sites.…”

“…Recent studies have shown that hydraulic-fracture operations could induce LPLD tremor-like events (Das and Zoback, 2013a,b;Hu et al, 2017). Although some LPLD events in their studies might be small regional earthquakes (Caffagni et al, 2015;Chen et al, 2018), the characteristics of the LPLD events observed in this study are different from any of them.…”

“…Shallow long-period long-duration (LPLD) tremor-like events have not been widely observed at major faults in continental settings, although episodic creep and slow-slip events have long been reported along several plateboundary faults that creep at shallow depths (Linde et al, 1996;Wei et al, 2013;Schwartz, 2015;Harris, 2017). On the other hand, similar LPLD events at shallower depths have been observed during slow-moving landslides and glaciers (Helmstetter and Garambois, 2010;Gomberg et al, 2011;Winberry et al, 2013), as well as during hydraulic fracturing operations in oil fields (Kanamori and Hauksson, 1992;Das and Zoback, 2013a,b;Hu et al, 2017).…”

“…The significant increase in small-to moderate-size earthquakes in Oklahoma since 2009 was mostly attributed to wastewater injections after shale gas developments in that region (Ellsworth, 2013;Keranen et al, 2014). Motivated by recent laboratory and field observations of tremor-type events during aseismic slip induced by fluid injections (Zigone et al, 2011;Guglielmi et al, 2015;Hu et al, 2017), our initial target was to identify potential tremor-like signals recorded by the dense nodal array in Oklahoma (Li et al, 2017). In the following sections, we first apply a recently developed local similarity method (Li et al, 2018) to identify LPLD tremor-like signals and then analyze their frequency content, wavespeed, and direction.…”

Fluid Injection and the Mechanics of Frictional Stability of Shale‐Bearing Faults

“…However, during hydraulic fracturing of shale reservoirs, the moment released by microearthquakes within the stimulated rock volume is much smaller than theoretical prediction based on the amount of fluid injected in the formation, revealing an energy deficit (e.g., Das & Zoback, 2013;Goodfellow et al, 2015;Kumar et al, 2017;Warpinski et al, 2012). Recently, it has been shown that this energy deficit is related with other deformation mechanisms associated with slow but accelerated shear slip along preexisting faults (Boroumand & Eaton, 2012;Caffagni et al, 2016;Das & Zoback, 2013;Eaton et al, 2013;Hu et al, 2017;Kumar et al, 2017;McGarr & Barbour, 2018;Zecevic et al, 2016). In addition, long-period long-duration (LPLD) events are commonly observed during the hydraulic stimulation of shale reservoirs and they have similar characteristics as tectonic tremors observed during slow-slip events at the plate boundary (Kumar et al, 2017).…”