Stabilization of fault slip by fluid injection in the laboratory and in situ

Abstract

Faults can slip seismically or aseismically depending on their hydromechanical properties, which can be measured in the laboratory. Here, we demonstrate that fault slip induced by fluid injection in a natural fault at the decametric scale is quantitatively consistent with fault slip and frictional properties measured in the laboratory. The increase in fluid pressure first induces accelerating aseismic creep and fault opening. As the fluid pressure increases further, friction becomes mainly rate strengthening, favoring aseismic slip. Our study reveals how coupling between fault slip and fluid flow promotes stable fault creep during fluid injection. Seismicity is most probably triggered indirectly by the fluid injection due to loading of nonpressurized fault patches by aseismic creep.

Seismic Response to Injection Well Stimulation in a High‐Temperature, High‐Permeability Reservoir

“…While these temperatures could be interpreted to be near the brittle-ductile transition for quartz-bearing rock (e.g., Scholz, 1988), this is unlikely given that seismicity at the nearby (and lithologically similar) Rotokawa geothermal field occurs in host rock with measured temperatures in excess of 330 • C . In addition, recent results have shown that a significant portion of induced seismicity may be triggered not by pore pressure perturbation, implying hydraulic connection to a wellbore, but by static and dynamic stress transfer onto suitably oriented fractures outside the reservoir (e.g., Cappa et al, 2019;Riffault et al, 2018). In addition, recent results have shown that a significant portion of induced seismicity may be triggered not by pore pressure perturbation, implying hydraulic connection to a wellbore, but by static and dynamic stress transfer onto suitably oriented fractures outside the reservoir (e.g., Cappa et al, 2019;Riffault et al, 2018).…”

“…The advance of the induced pressure front is controlled by the hydraulic diffusivity of the reservoir (also referred to as transmissivity, the permeability thickness product: kh), which is closely linked to the reservoir permeability. However, a variety of mechanisms are responsible for triggering seismicity, many of which are unrelated to the hydraulic properties of the reservoir, leading to speculation as to the utility of SBRC (Cappa et al, 2019;Riffault et al, 2018). At Ngatamariki, and at most other naturally fractured reservoirs, flow is strongly influenced by the spacing and permeability of fractures (Grant & Bixley, 2011).…”

“…If we consider an alternative scenario, in which NM08 was always hydraulically connected to the fracture zone, then we would expect seismicity to have been triggered by the diffusion of the maximum observed WHP to the fracture zone (2.6 MPa during NF; Figure 5). It may also be the case that undetected seismic (or entirely aseismic) slip/opening near the wellbore transferred stress onto a remote, hydraulically isolated fracture zone, triggering failure (e.g., Cappa et al, 2019;Rinaldi & Rutqvist, 2019). It may also be the case that undetected seismic (or entirely aseismic) slip/opening near the wellbore transferred stress onto a remote, hydraulically isolated fracture zone, triggering failure (e.g., Cappa et al, 2019;Rinaldi & Rutqvist, 2019).…”

“…Recent research by Cappa et al (2019) shows that fluid injection can encourage rate-strengthening behavior of a fracture, implying that seismic slip, even on a targeted fracture or fault, is triggered by poroelastic stress transfer away from the pressurized zone due to aseismic, near-well displacement. Therefore, an alternative explanation for the triggering of seismicity at NM08 never requires a hydraulic connection between the well and the seismically active zone.…”

Deciphering the Stress State of Seismogenic Faults in Oklahoma and Southern Kansas Based on an Improved Stress Map

“…While previous studies have provided overall knowledge of the ambient stress field in Oklahoma and southern Kansas, a high‐resolution stress map is needed to systematically assess fault criticality under the local stress field. This is especially important with the growing evidence that poroelastic stress (e.g., Barbour et al, ; Deng et al, ; Goebel et al, ; Segall & Lu, ) and aseismic creep propagation (e.g., Cappa et al, ; Eyre et al, ) could, in part, drive some of the induced seismicity. In this study, we develop a stress map with relatively high spatial resolution using a suite of 2,047 focal mechanism solutions obtained from Oklahoma and southern Kansas, allowing for more precise quantitative analysis of the fault stress state.…”