Numerical Simulation of Water-Rock Interaction through an Artificial Water Circulation in a Hot Dry Rock

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  • 高温岩体貯留層内の岩石相互作用に関する数値シミュレーション

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Abstract

A numerical simulator was developed to analyze the coupled hydrological-thermalchemical processes encountered in a heat extraction system used from a hot dry rock reservoir. In this system, cold water is injected into a re-injection well drilled in a hot dry rock reservoir that has an artificially created fracture, and steam or hot water is recovered from a production well located a few hundred meters from the re-injection well. Fluid, energy, and chemical transport processes in the fracture are described as a two-dimensional problem, and energy transport processes in the rock matrix as a three-dimensional one. The convection-diffusion type equations used to model these transport processes are solved numerically by a finite difference method.<BR>The effect of temperature on the precipitation and dissolution of silica was investigated for various injected silica concentrations. Fracture aperture decreases in the low temperature region near the re-injection well due to the precipitation of silica, whereas in the high temperature region it increases due to the dissolution of silica. The temperature dependence of precipitation and dissolution rates was confirmed by the numerical simulator. Numerical analysis, however, shows that the dissolution and deposition of silica resulted in very small change in the fracture permeability after injecting water for 1,800 days.

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