Abstract

The geothermal energy extraction using the fracture-type reservoir in deep crust more than 350–400 °C is suggested. When using the fracture-type reservoir, there is a possibility of aseismic slip rather than seismic slip. However, characteristic and influence on permeability of the aseismic slip is unknown. Therefore, in this study, to clarify the occurrence condition, characteristics and influence on permeability of aseismic slip, injection-induced slip experiment using cylindrical specimen with a 45° tilted tensile fracture was conducted under the condition 200–500 °C. As a result, the followings were clarified. 1) there was a difference in characteristics between the slip start and the subsequent slip, 2) the slip velocity at the beginning of slip was affected by the surface shape of the fracture, 3) and the slip velocity of the subsequent steady slip tended to decrease as the temperature increased. Under 350–500 °C, the pore pressure at the beginning of slip decreased as temperature increased. Therefore, it is suggested that slower slip with a smaller pore pressure, namely, a more stable slip, may occur as the temperature increases. The permeability change before and after the slip experiment was increased at 200, 250 and 300 °C, didn't change at 350 °C and decreased by half at 500 °C. But since it is not a large decrease of more than one order, it is considered that a sufficient permeability can be maintained in the real geothermal reservoir.

1.
Introduction

New concept of engineered geothermal development where reservoirs are created in ductile basement is proposed (Asanuma et al., 2012). This potentially has a number of advantages. Suppression of felt earthquakes from/around the reservoirs is one of them (Muraoka et al., 2013). When using this type reservoir, there is a possibility of aseismic slip rather than seismic slip. However, characteristic and influence on permeability of the aseismic slip is unknown. Therefore, in this study, to clarify the occurrence condition, characteristics and influence on permeability of aseismic slip, injection-induced slip experiment using cylindrical specimen with a 45° tilted tensile fracture was conducted under the condition 200–500 °C.

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