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Application of Water Fracturing in Geothermal Energy Mining: Insights from Experimental Investigations

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College of Construction Engineering, Jilin University, Changchun 130026, China
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Key Lab of Groundwater Resource and Environment Ministry of Education, Jilin University, Changchun 130026, China
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Center for Hydrogeology and Environmental Geology Survey, China Geological Survey, Baoding 071051, China
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Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang 050061, China
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National Hot Dry Rock Technology Innovation Platform Breeding Base, Shijiazhuang 050003, China
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Authors to whom correspondence should be addressed.
Energies 2019, 12(11), 2138; https://doi.org/10.3390/en12112138
Received: 30 April 2019 / Revised: 26 May 2019 / Accepted: 28 May 2019 / Published: 4 June 2019
Currently, water fracturing under deep geothermal conditions remains poorly understood because the reservoir rocks are usually high-strength crystalline rocks characterized by high temperatures. The aim of this study is to investigate the effects of rock properties, injection rates, and temperatures on hydraulic fracturing behavior and the induced crack characteristics through experimental investigations. A series of hydraulic fracturing experiments was conducted on two Indosinian granite types to investigate the differences in hydraulic fracturing behavior caused by rock properties. Among others, six samples were tested under a room-temperature condition at different injection rates from 1 to 30 mL/min to clarify the effect of the injection rate and three samples were tested under a high-temperature condition (150 °C) to simulate specific geothermal environments. The results indicated that granites with different rock properties have different injection rate thresholds. When the injection rate is below the threshold, the injection pressure finally reached a constant value without fracturing. For rocks with the same properties, the temperature effect can lead to a high injection rate threshold due to the occurrence of thermally-induced cracks. The number of acoustic emission events recorded during the room-temperature experiments increased linearly with increasing injection rate, while high-temperature tests increased sharply. The investigation results imply that a complex hydraulically-induced crack network is expected to be achieved in geothermal reservoirs by a high injection rate or high temperature differences (between injected fluid and rock). Additionally, the characteristics of the hydraulically-induced cracks were investigated by cutting through the sample blocks and measuring the residual pressure. The results indicated that the induced crack aperture can maintain a fluid conductivity of 0.1–0.8 mm/s at a closure pressure of 12 MPa. View Full-Text
Keywords: water fracturing; granite; geothermal; rock properties; high temperature; injection rate water fracturing; granite; geothermal; rock properties; high temperature; injection rate
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Lei, Z.; Zhang, Y.; Hu, Z.; Li, L.; Zhang, S.; Fu, L.; Yue, G. Application of Water Fracturing in Geothermal Energy Mining: Insights from Experimental Investigations. Energies 2019, 12, 2138.

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