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Frictional and Poromechanical Properties of the Delaware Mountain Group: Implications for Seismic and Aseismic Faulting Associated With Induced Earthquakes

Description: 

Tectonic faults can slip through a spectrum of slip modes depending upon their frictional properties and the elastic stiffness surrounding the fault zone. Hence, quantifying the frictional properties of fault zones under in-situ conditions is critical for determining what conditions permit stable (aseismic) or unstable (earthquake rupture) behavior. In the southern Delaware Basin (DB) of west Texas there is a widespread system of steeply-dipping faults that have been made neotectonically active by injection, production and hydraulic fracturing. InSAR and seismic data show that the faults host seismic and aseismic slip, however the frictional properties that permit these different slip modes is not well understood. Here, we measure rate and state frictional properties with velocity stepping and slide-hold-slide experiments conducted on Delaware Mountain Group (DMG) cores that delineate the southern DB. Experiments were conducted inside a true-triaxial pressure vessel in a double direct shearing configuration at the Penn State University Rock and Sediment Mechanics Laboratory. Our data show that the DMG is frictionally weak, with steady-state coefficients of friction of 0.3 – 0.5. Most samples show a systematic progression from velocity strengthening to velocity neutral behavior as function of increasing slip displacement. This is consistent with the idea that fault zone maturity and shear localization play key roles in modulating frictional behavior and fault stability. In addition, we observe a systematic increase in volumetric flow rate at the upstream reservoir due to a step increase in sliding velocity. Presumably, the fault zone dilates during the velocity step, causing a local reduction in pore-fluid pressure, and thus, a local increase in effective normal stress and frictional strength. The poromechanical properties are in agreement with the velocity strengthening behavior of the cores. Broadly speaking, our data are consistent with the lack of seismic activity along the northern extent of the southern DB and suggest that tectonic faulting within this region should favor aseismic creep.

Session: Advances in Characterizing Seismic Hazard and Forecasting Risk in Hydrocarbon Systems

Type: Oral

Date: 4/18/2023

Presentation Time: 05:00 PM (local time)

Presenting Author: Chas Bolton

Student Presenter: No

Invited Presentation: 

Authors