The Role of Mineral Composition on the Frictional and Stability Properties of Powdered Reservoir Rocks

Abstract

The growing hazard of induced seismicity driven by the boom in unconventional resources exploitation is strongly linked to fault activation. We perform laboratory measurements on simulated fault gouges comprising powdered reservoir rocks from major oil and gas production sites in China, to probe the control of mineral composition on fault friction and stability responses during reservoir stimulation. Double direct shear experiments were conducted on gouges with phyllosilicate content ranging from 0 to 30 wt.% and grain sizes <150 μm, at constant normal stresses of 10–40 MPa and conditions of room temperature and water saturation. The velocity step and slide‐hold‐slide sequences were employed to evaluate frictional stability and static healing, respectively. Results indicate that the mineralogy of the gouges exhibit a strong control on the frictional strength, stability, and healing. Phyllosilicate‐rich samples show lower frictional strength μ and higher values of (a − b), promoting stable sliding. For the gouges studied, the frictional strength decreases monotonically with increasing phyllosilicate content, and a transition from velocity weakening to velocity strengthening behavior is evident at 15 wt.% phyllosilicates. Intermediate healing rates are common in gouges with higher content of phyllosilicates, with high healing rates predominantly in phyllosilicate‐poor gouges. As an indispensable component in reservoir rocks, the carbonates are shown to affect both the frictional stability and healing response. These findings can have important implications for understanding the effects of mineralogy on fault behavior and induced seismic potential in geoengineering activities, particularly in reservoirs in China.

Friction of Longmaxi Shale Gouges and Implications for Seismicity During Hydraulic Fracturing

“…The experimental data presented in this study indicate that the frictional properties of Longmaxi shale are heterogeneous and potentially unstable layers exist in the formation. One potential mechanism (Figure 16) is where fluid injection drives slip on aseismic faults with stress transfer onto adjacent for gouges with different proportions of tectosilicates and pyrite, phyllosilicates and TOC, and carbonates both from this study and previous laboratory results (Boulton et al, 2012;Fang et al, 2016;Giorgetti et al, 2015;Kohli & Zoback, 2013;Moore & Lockner, 2011;Zhang et al, 2019). The red symbols in the left panel indicate μ > 0.5, and the green symbols represent μ < 0.5.…”

“…Figure 15. (left) Frictional strength μ and (right) frictional stability (a − b) for gouges with different proportions of tectosilicates and pyrite, phyllosilicates and TOC, and carbonates both from this study and previous laboratory results(Boulton et al, 2012;Fang et al, 2016;Giorgetti et al, 2015;Kohli & Zoback, 2013;Moore & Lockner, 2011;Zhang et al, 2019). The red symbols in the left panel indicate μ > 0.5, and the green symbols represent μ < 0.5.…”

“…These shales are highly variable in composition and cover the majority of the ternary space of Figure 14. We further compare the measured frictional strength μ and stability (a − b) for different fault gouges with varied proportions of this ternary group of minerals, both from this study and from previous studies (Boulton et al, 2012;Fang et al, 2017;Giorgetti et al, 2015;Kohli & Zoback, 2013;Moore & Lockner, 2011;Zhang et al, 2019) in Figure 15. Compared with phyllosilicate and TOC-rich gouges (top vertex of the ternary plot), the tectosilicate and pyrite-rich (basal left vertex) and carbonate-rich (basal right vertex) gouges generally exhibit higher frictional strength μ and lower frictional stability (a − b) manifested as velocity-weakening behavior.…”

“…With the growth in shale gas recovery, more attention has been applied to understanding the frictional and stability properties of shale fault gouges and fractures that are implicated in injection‐induced seismicity (Fang et al, 2017; Jia et al, 2019; Kohli & Zoback, 2013; Scuderi & Collettini, 2018; Shen et al, 2019; Zhang et al, 2019). These studies have identified relationships between mineral composition and the frictional characteristics of shale gouges/fractures in a variety of experimental configurations and boundary conditions (e.g., applied stresses, humidity, and shear velocities).…”

Temperature and Fluid Pressurization Effects on Frictional Stability of Shale Faults Reactivated by Hydraulic Fracturing in the Changning Block, Southwest China

“…There is growing interest in understanding the mechanisms of induced seismicity associated with shale gas extraction. At room temperature, the frictional strength and stability of powdered shale gouge are dependent on the mineralogy of the gouge, primarily the phyllosilicates and organic carbon (Fang et al, 2017; Kohli & Zoback, 2013; Zhang, An, et al, 2019). With an increase in pore fluid pressure, phyllosilicate‐rich shale gouges do not weaken but instead promote aseismic creep (de Barros et al, 2016; Scuderi & Collettini, 2018).…”