A mechanistic model for compaction of granular aggregates moderated by pressure solution

Abstract

1] A model is presented for the compaction of granular aggregates that accommodates the serial processes of grain-contact dissolution, grain-boundary diffusion, and precipitation at the pore wall. The progress of compaction and the evolution of the mass concentration of the pore fluids may be followed with time, for arbitrary mean stress, fluid pressure, and temperature conditions, for hydraulically open or closed systems, and accommodating arbitrary switching in dominant processes, from dissolution, to diffusion, to precipitation. Hindcast comparisons for compaction of quartz sands [Elias and Hajash, 1992] show excellent agreement for rates of change of porosity, the asymptotic long-term porosity, and for the development of silica concentrations in the pore fluid with time. Predictions may be extended to hydraulically open systems where flushing by meteoric fluids affects the compaction response. For basins at depths to a few kilometers, at effective stresses of 35 MPa, and temperatures in the range 75°-300°C, rates of porosity reduction and ultimate magnitudes of porosity reduction increase with increased temperature. Ultimate porosities asymptote to the order of 15% (300°C) to 25% (75°C) at the completion of dissolution-mediated compaction and durations are accelerated from a few centuries to a fraction of a year as the temperature is increased. Where the system is hydraulically open, flushing elevates the final porosity, has little effect on evolving strain in these precipitation-controlled systems, and depresses pore fluid concentrations. These effects are greatest at lower temperatures.

Spontaneous Switching between Permeability Enhancement and Degradation in Fractures in Carbonate: Lumped Parameter Representation of Mechanically- and Chemically-Mediated Dissolution

“…the validity of Equation (A7)), is supported by the experimental data (see Table I and Figure 2 in Yasuhara et al (2003)). In defining mass redistribution, it is sometimes convenient to relate dissolution mass fluxes, dM…”

The Role of Pressure Solution Creep in the Ductility of the Earth’s Upper Crust

“…The parameters may be calculated from measurable quantities in this phenomenological model and were used for comparison with quartz compaction data. The model has been modified and refined by others (Taron and Elsworth, 2010;Yasuhara et al, 2003) to include the strain hardening effect of growing grain contact areas. The idea of finding a time scale for the transition between viscous and plastic is intriguing, it would help analysis and application of compaction data, but the basis of this model is in our opinion incorrect: a plastic pore compressibility does not relieve stress from the grain contacts where pressure solution occurs, in other words the viscous and plastic elements should be in series, not in parallel.…”

Reaction-driven casing expansion: potential for wellbore leakage mitigation

“…[73]). This presumably is weak and deforms by frictional granular flow or even diffusion or pressure solution accommodated granular flow [96,131]. Accordingly, the Ca(OH) 2 phase could easily become extruded from hydrating CaO grain contacts into the intervening pores, leading to mechanical compaction of the CaO framework and to a reduction in sample porosity and permeability.…”