Pressure Solution Compaction During Creep Deformation of Tournemire Shale: Implications for Temporal Sealing in Shales

Abstract

The temporal evolution of gouge compaction determines fluid transfer and rock rupture dynamics. Thus, studies on the time‐dependent creep compaction processes of shale materials may elucidate the chemo‐mechanical behavior of shallow clay‐rich zones. We investigated this problem by combining creep experiments conducted in triaxial compression under upper crustal conditions with modeled pressure solution processes in Tournemire shale. The shale samples were deformed parallel and perpendicular to the bedding at low (10 MPa, 26°C, this study) and high (80 MPa, 26°C, published by Geng et al., 2018, https://doi.org/10.1029/2018JB016169) pressures. We monitored the deformation during stepping creep experiments until sample failure. Our results differ from those of traditional creep experiments and show that the creep failure strength of Tournemire shale samples increased significantly (by ∼64%) at both pressures. Our experiments suggest that at appropriate temperatures, the pressure solution is highly active and is the dominant temporal sealing mechanism in the shale. Using our experimental data and the statistical rock physics method, we modeled the temporal reduction of effective porosity in terms of depth and temperature. Our thermal‐stress coupled modeling results suggest that the pressure solution induced sealing is the most active at middle‐shallow depths (∼3.8 km). We believe that the sealing capacity and creep failure strength of dolomite‐rich shales may change significantly at middle‐shallow depths, indicating an important influence on reservoir fluids transfer and fault gouge strength.

Strain Partitioning and Frictional Behavior of Opalinus Clay During Fault Reactivation

“…The resulting Error bars lie within the symbol size stress exponents are significantly higher compared to the characteristic stress exponents (n < 5) for pressure solution Schutjens 1991;Zhang and Spiers 2005;Zhang et al 2010;Geng et al 2018) or stress exponents inferred for dislocation creep in calcite or quartz (Hirth and Tullis 1992;Renner et al 2002). Stress exponents with n > 10 were used to describe the brittle creep of different sandstones with n = 20 -70 Heap et al 2009a, b), Tavel limestone with n = 40-66 (Nicolas et al 2017), Westerly granite n = 59-64 (Lockner 1993) and Tournemire shale with n = 27-63 (Geng et al 2018;Geng et al 2021). These studies interpret determined stress exponents to be indicative of stress-and temperaturedependent, sub-critical crack growth by stress corrosion (Atkinson 1984) as governing deformation mechanism.…”

A Viscoplasticity Model for Shale Creep Behavior and Its Application on Fracture Closure and Conductivity

“…The bedding planes and the fractures within them are the main sources of creep anisotropy [10], and the results of many shale creep experiments show that the strain of shale in the horizontal bedding sample is larger than that in the vertical bedding sample [4,21]. Shale comprises hard materials (quartz, feldspar, and pyrite) and soft materials (clay, kerogen, etc.).…”