Reactive transport at stressed grain contact and creep compaction of quartz sand

Abstract

[1] A kinetic model is developed to investigate intergranular pressure solution. This model couples stress-induced dissolution at grain contacts, diffusion through grain boundaries, and precipitation in pore spaces. The rate-controlling processes are evaluated according to the dimensionless concentrations at grain contacts and in the pore fluid. Constrained by the experimental results of creep compaction of quartz sands, calculations suggest that the equilibrium concentration at stressed grain contacts (c eqb ) does not exceed 1 order of magnitude higher than the hydrostatic equilibrium concentration (c eq ) at the initial stages of creep compaction. However, c eqb decays rapidly with increasing compaction and becomes close to c eq after several percent strain. The diffusivity at grain contacts is 1-2 orders of magnitude lower than the diffusivity in pore fluid. The rate-controlling process is related to grain size and strain. An increase in grain size shifts the systems toward the diffusion-controlled regime, while an increase in strain shifts the systems from dissolution-controlled regime toward either diffusion-controlled regime (larger grains) or precipitation-controlled regime (smaller grains).Intergranular pressure solution appears to be very sensitive to pore-fluid chemistry. Even a slight supersaturation in the pore fluid could prevent the diffusion along grain contacts. This may explain why the strength of intergranular pressure solution varies widely in natural sandstones.

Time‐Dependent Consolidation in Porous Geomaterials at In Situ Conditions of Temperature and Pressure

“…Previous experimental work has demonstrated that for isostatic consolidation tests on wet sand at 20, 150, and 225°C, the plastic strain curves are approximately linear and parallel in log stress for Regime 1, consistent with the Bjerrum plot (Karner et al, 2008). Overall, the strain rate, temperature, and chemical effects observed for sand and documented by Karner et al (2008), Chester et al (2004Chester et al ( , 2007, and He et al (2013), likely can be represented in a Bjerrum plot based on the parameters varied.…”

“…Although stress has primary control on brittle deformation in sand, much experimental work has shown that compaction of sand also depends on strain rate, temperature, and chemical environment Chester et al, 2004Chester et al, , 2007Dewers & Hajash, 1995;Dove, 1995;Elias & Hajash, 1992;He et al, 2003He et al, , 2013Karner et al, 2008;Rutter & Wanten, 2000). The elliptical cap describing shear-enhanced compaction collapses to lower stresses with corresponding decreases in P* at elevated temperatures in wet sand (Dewers & Hajash, 1995;Karner et al, 2008) and sandstone (Baud et al, 2000;Wong & Baud, 2012).…”

Fracture transmissivity evolution due to silica dissolution/precipitation during geothermal heat extraction

“…These deviations generally occur due to differences between the injected and initial concentration and temperature. The reaction rate (mol/m 2 s) is calculated by (He et al, 2013):…”

Hydraulic sealing due to pressure solution contact zone growth in siliciclastic rock fractures

“…With respect to the observed broadening of the contact stress distribution as smaller roughness features are being accounted for, the exponential dependency in equation highlights the sensitivity of dissolution rates on the roughness wavelength spectrum, as illustrated in Figure . The temperature‐dependent diffusion constant, (m 2 s −1 ), varies over the fracture surface field: where 0 < f < 1 is a scaling constant that expresses the reduced diffusivity of the compressed contact zone with respect to the free pore space [ Revil , ; He et al , ]. A harmonic average is used for the diffusion coefficient at the interface between the contact zone and the free fluid.…”

“…where 0 < f < 1 is a scaling constant that expresses the reduced diffusivity of the compressed contact zone with respect to the free pore space [Revil, 2001;He et al, 2013]. A harmonic average is used for the diffusion coefficient at the interface between the contact zone and the free fluid.…”