Experimental investigation on thermal cracking, permeability under HTHP and application for geothermal mining of HDR

Yangsheng Zhao, Zijun Feng, Yu Zhao and Zhijun Wan

Energy, 2017, vol. 132, issue C, 305-314

Abstract: Thermal cracking behavior of granite at high temperature and high pressure (HTHP) is the key to the performance of Hot Dry Rock (HDR) geothermal energy extraction system. In this study, permeability tests accompanying acoustic emission (AE) tests in granites are first conducted under HTHP by 600 °C 20MN servo control rock triaxial testing machine. The test results show that granites, nearly impermeable rocks, can show a striking increase of permeability by heating from the critical temperature. The growth curve of granite permeability shows two phases because of the multi-period of thermal-cracking in the heating process from room temperature to 500 °C. The coupled effect of temperature and pressure shows that critical temperature of permeability change decreases with increasing confining pressure. Then, a detailed characterization of the sample microstructure is presented using Micro-CT method. It is discovered that thermal cracking mainly occurs at grain boundaries in forms of inter-granular microcracks along apparent weaknesses, and develops with increasing temperature. Meanwhile intra-granular cracks are observed when heating to 500 °C, indicating that thermal cracking in granite under HTHP is induced by both intra-granular and inter-granular thermal stress. At last, experimental stimulation and application for geothermal mining of HDR are discussed.

Keywords: Thermal cracking; Permeability; AE event; Micro-CT; Hot Dry Rock (search for similar items in EconPapers)
Date: 2017
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (11)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:132:y:2017:i:c:p:305-314

DOI: 10.1016/j.energy.2017.05.093

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