Laboratory Investigation of Cryogenic Fracturing Effect of Hot Dry Rock Wellbores Under Triaxial-Confining Stresses

Abstract

Hot dry rock (HDR) contains abundant thermal energy, which can be extracted through fracturing and used for electricity generation. Due to its deep depth, high-temperature and high-pressure conditions, it is difficult to initiate fractures for conventional hydraulic fracturing technology. This paper study the advantage of cryogenic fracturing on the HDR. We conducted a series of laboratory experiments on rock samples with different length of open-hole under triaxial-confining stresses (10 MPa). The nitrogen fracturing wellbores of high temperature (100–300 ℃) granites were treated with LN (liquid nitrogen) and NO-LN and retained with 20 mm and 30 mm open-hole to form four control groups. The fracturing results show that LN cryogenic stimulation is more effective in reducing the HDR initiation pressure. When the open-hole is 20 mm, the breakdown pressure of samples with LN decreases by 13.9%–18.7% compared with untreated samples. When the open-hole changed from 20 mm to 30 mm, the breakdown pressure of samples with NO-LN are reduced by 6.7%–15%. The samples with a 30 mm open-hole inside the wellbore formed complex fracture patterns after the nitrogen fracturing. This could be attributed to the longer open-hole, the more complex micro-fractures on the surface and the force of the direction parallel to the cross section is significantly increased.

Copyright 2023, IFEDC Organizing Committee.

This paper was prepared for presentation at the 2023 International Field Exploration and Development Conference in Wuhan, China, 20–22 September 2023.

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