Experimental Study and Numerical Simulation of Rock Fracture Caused by Rapid Decompression of Sub / Supercritical Fluid

Abstract

Geothermal energy is remarkable as a clean and renewable energy source. Most of the existing geothermal power plants utilize steam and hot water from hydrothermal reservoirs. Recent data showed that intrusive rock body with supercritical fluid may exist at the bottom of old volcanos. Large power generation and suppression of felt earthquake can be expected, if we can develop the supercritical resources. For the development of supercritical geothermal resources, it is necessary to create high permeable fracture networks by well stimulation. Hydraulic fracturing is one of the most practical methods for well stimulation. We have conducted hydrothermal experiments using granite sample and observed tensile fracture by thermal stress by liquid/vapor phase transition with temperature drop by rapid decompression (Flash) in sub/supercritical condition. And we proposed a conceptual idea of flash fracturing technology for developing high temperature high pressure (deep) geothermal reservoir. However, the experimental conditions of our previous studies are limited and none of these studies have revealed the mechanism of flash fracturing. Therefore, we conducted rapid decompression experiments at more conditions. Moreover, FEM simulation analysis for rapid cooling rock is carried out to consider the mechanism of rock fracturing by thermal stresses due to rapid decompression. This article is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).