Mechanism of fracture permeability in crystalline rock under controlled stress and temperature conditions

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In this study, flow-through experiments on a single fracture in granite has been carried out under confining pressures of 5-10 MPa, and at temperatures of 20-90℃. The fracture aperture and the permeability monotonically decreased with time at room temperature, and reached a quasi-steady state. Then, after the temperature was raised to 90℃, the aperture decreased again throughout the rest of the experiments. Fluid samples were taken from the outlet to examine the elemental concentrations that were evaluated by inductively-coupled plasma atomic emission spectrometry(ICP-AES). The elemental concentrations increased with increase of temperature. After the flow-through experiments, the fracture surface was observed by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy(SEM-EDX). The formation of a few kinds of precipitated minerals such as silica and calcite was revealed. The precipitation was limited to quite local and small areas. However, the precipitated minerals seemed to have had some influences on the permeability.