Continental crust at temperatures > 400 °C and depths > 10–20 km normally deforms in a ductile manner, but can become brittle and permeable in response to changes in temperature or stress state induced by fluid injection. In this study, we quantify the theoretical power generation potential of an enhanced geothermal system (EGS) at 15–17 km depth using a numerical model considering the dynamic response of the rock to injection-induced pressurization and cooling. Our simulations suggest that an EGS circulating 80 kg s−1 of water through initially 425 ℃ hot rock can produce thermal energy at a rate of ~ 120 MWth (~ 20 MWe) for up to two decades. As the fluid temperature decreases (less than 400 ℃), the corresponding thermal energy output decreases to around 40 MWth after a century of fluid circulation. However, exploiting these resources requires that temporal embrittlement of nominally ductile rock achieves bulk permeability values of ~ 10–15–10–14 m2 in a volume of rock with dimensions ~ 0.1 km3, as lower permeabilities result in unreasonably high injection pressures and higher permeabilities accelerate thermal drawdown. After cooling of the reservoir, the model assumes that the rock behaves in a brittle manner, which may lead to decreased fluid pressures due to a lowering of thresholds for failure in a critically stressed crust. However, such an evolution may also increase the risk for short-circuiting of fluid pathways, as in regular EGS systems. Although our theoretical investigation sheds light on the roles of geologic and operational parameters, realizing the potential of the ductile crust as an energy source requires cost-effective deep drilling technology as well as further research describing rock behavior at elevated temperatures and pressures.

中文翻译：

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水文对韧性地壳增强地热系统潜力的限制

温度 > 400 °C 和深度 > 10-20 km 的大陆地壳通常会以延性方式变形，但会因流体注入引起的温度或应力状态变化而变得脆性和可渗透。在这项研究中，我们使用数值模型量化了 15-17 公里深度的增强型地热系统 (EGS) 的理论发电潜力，该模型考虑了岩石对注入引起的加压和冷却的动态响应。我们的模拟表明，EGS 将 80 kg s−1 的水循环通过最初 425 ℃ 的热岩，可以以 ~ 120 MWth (~ 20 MWe) 的速率产生热能长达二十年。随着流体温度降低（低于400℃），经过一个世纪的流体循环后，相应的热能输出减少到40MWth左右。然而，开发这些资源要求名义上延性岩石的时间脆化在尺寸约为 0.1 km3 的岩石体积中达到约 10-15-10-14 m2 的体积渗透率值，因为较低的渗透率会导致不合理的高注入压力和较高的渗透率加速热下降。储层冷却后，该模型假设岩石呈脆性行为，这可能会由于临界应力地壳破裂阈值的降低而导致流体压力降低。然而，这种演变也可能增加流体路径短路的风险，就像在常规 EGS 系统中一样。尽管我们的理论研究揭示了地质和操作参数的作用，但要实现韧性地壳作为能源的潜力，需要具有成本效益的深钻技术以及描述岩石在高温和高压下行为的进一步研究。