How to Seal Hydraulic Fracturing Boreholes in the Large-Size HDR Rocks under HTHP Conditions

The hydraulic fracturing (HF) is a key technique to enhance the permeability and heat production of hot-dry-rock (HDR) geothermal reservoirs. Normally, laboratory HF tests should be preconducted to understand the HF characteristics of HDR samples. However, in the laboratory test, sealing failure between boreholes and injection pipes always limits the experimental efficiency and data accuracy, especially for the HF tests under high-temperature and high-pressure (HTHP) conditions. Traditional sealing methods, such as rubber and cement sealing, are easy to be failed because of their poor load and/or thermal bear performance under HTHP conditions. Therefore, in this study, we proposed a novel HTHP seal by using wedge-buckled copper components and steel rings. The sealing efficiency was verified by successfully conducting the HF tests of HDR rocks with a dimension of φ200×400 mm under various high temperatures ranging from 100°C to 400°C. As expected, the unfavorable factors such as HTHP and high injection pressure could be turned into favorable ones during the introduced seal method. By this investigation, we expect to provide some sealing solutions for researchers when conducting HF tests under HTHP environments.