Cloud-fracture networks as a means of accessing superhot geothermal energy

Noriaki Watanabe, Kiyotoshi Sakaguchi, Ryota Goto, Takahiro Miura, Kota Yamane, Takuya Ishibashi, Youqing Chen, Takeshi Komai, Noriyoshi Tsuchiya

Research output: Contribution to journalArticlepeer-review

29 Citations (Scopus)


Superhot geothermal environments (above ca. 400 °C) represent a new geothermal energy frontier. However, the networks of permeable fractures capable of storing and transmitting fluids are likely to be absent in the continental granitic crust. Here we report the first-ever experimental results for well stimulation involving the application of low-viscosity water to granite at temperatures ≥400 °C under true triaxial stress. This work demonstrates the formation of a network of permeable microfractures densely distributed throughout the entire rock body, representing a so-called cloud-fracture network. Fracturing was found to be initiated at a relatively low injection pressure between the intermediate and minimum principal stresses and propagated in accordance with the distribution of preexisting microfractures, independent of the directions of the principal stresses. This study confirms the possibility of well stimulation to create excellent fracture patterns that should allow the effective extraction of thermal energy.

Original languageEnglish
Article number939
JournalScientific Reports
Issue number1
Publication statusPublished - 2019 Dec 1


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