Department of Environmental Studies for Advanced Society, Graduate School of Environmental Studies, Tohoku University, Sendai, 9808579, Japan.
Fukushima Renewable Energy Institute, National Institute of Advanced Industrial Science and Technology (AIST), Koriyama, 9630298, Japan.
Sci Rep. 2019 Jan 30;9(1):939. doi: 10.1038/s41598-018-37634-z.
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.
超高温地热环境（高于约 400°C）代表了一种新的地热能源前沿。然而，在大陆花岗质地壳中，可能不存在能够储存和传输流体的可渗透裂缝网络。在这里，我们报告了有史以来首次在真三轴应力下将低粘度水应用于温度≥400°C 的花岗岩的井增产实验结果。这项工作证明了在整个岩体中形成了密集分布的可渗透微裂缝网络，这被称为云状裂缝网络。研究发现，裂缝是在中间主应力和最小主应力之间相对较低的注入压力下开始形成的，并按照预先存在的微裂缝的分布进行扩展，与主应力的方向无关。这项研究证实了进行井增产以形成可允许有效提取热能的优异裂缝模式的可能性。
