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 [] 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.
Abstract Geothermal reservoirs are significant sources of renewable energy. Accurate geometric modeling of these reservoirs is essential for understanding the distribution of heat and fluid dynamics within them. This study aims to develop a geometric model of the Sibayak geothermal field using borehole data. Borehole data provide detailed geological information, which is crucial for constructing a realistic geometric model. The methodology of this research involves several key steps: the collection of borehole data from the Sibayak geothermal field, the construction of a 3D geometric model of the reservoir using COMSOL Multiphysics based on the borehole data, and the validation of the model through comparison with field data and previous research findings. The results indicate that the developed geometric model successfully identifies zones with high geothermal potential and provides an accurate depiction of the reservoir’s boundaries and characteristics. Modeling the geometry of geothermal reservoirs using borehole data offers profound insights into the internal dynamics of the reservoir and can serve as a valuable tool for planning and optimizing geothermal energy exploitation.
Laboratory and field observations note the significant role of strength recovery (healing) on faults during interseismic periods and implicate pressure solution as a plausible mechanism. Plausible rates for pressure solution to activate, and the magnitudes of ultimate strength gain, are examined through slide‐hold‐slide experiments using simulated quartz gouge. Experiments are conducted on fine‐grained (110 μm) granular silica gouge, saturated with deionized water, confined under constant normal stress of 5 MPa and at modest temperatures of 20 and 65°C, and sheared at a maximum rate of 20 μm/s. Data at 20°C show a log linear relation between strength gain and the duration of holding periods, whereas the higher temperature observations indicate higher healing rates than the log linear dependencies; these are apparent for hold times greater than ∼1000 s. This behavior is attributed to the growth and welding of grain contact areas, mediated by pressure solution. The physical dependencies of this behavior are investigated through a mechanistic model incorporating the serial processes of grain contact dissolution, grain boundary diffusion, and precipitation at the rim of contacts. We use the model to predict strength gain for arbitrary conditions of mean stress, fluid pressure, and temperature. The strength gain predicted under the experimental conditions (σ eff = 5 MPa and T = 65°C) underestimates experimental measurements for hold periods of less than ∼1000 s where other frictional mechanisms contribute to strength gain. Beyond this threshold, laboratory observations resemble the trend in the prediction by our mechanistic model, implicating that pressure solution is likely the dominant mechanism for strength gain. The model is applied to the long‐term prediction of healing behavior in quartzite fault zones. Predictions show that both rates and magnitudes of gain in contact area increase with an increase in applied stresses and temperatures and that fault healing aided by pressure solution should reach completion within recurrence interval durations ranging from <1 to ∼10 4 years, depending on applied stresses, temperatures, and reaction rates.
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