The present study aims to understand the potential of a new and novel type of geothermal play system for high temperature and electricity production: crustal fault zones (CFZ). According to geological and geophysical data, the Pontgibaud fault zone (French Massif Central) is suspected to host an active hydrothermal system at a depth of a few kilometers. The deep geometry of the fault zone and the permeability distribution are the main unknown parameters that are required to assess the geothermal potential of the Pontgibaud site. Structural and thin-section observations, laboratory permeability and connected porosity measurements and X-ray micro-tomography observations suggest that the hydrothermal system behaves like a double matrix-fracture permeability reservoir. Numerical modeling in which we varied the fault dip and the ratio between the fault zone permeability and host rock, R, was performed. Results indicate that three main convective regimes can be identified (weak convection, single cellular-type convection and bicellular convection). For a sufficiently high fault zone permeability (> 1 × 10−15 m2), buoyancy-driven flow creates a positive thermal anomaly of several tens of °C at a depth of 2–5 km. For a vertical fault zone, the thermal anomaly is larger for higher R values. Numerical models, then applied to the geologically constrained Pontgibaud fault zone, show that a temperature of 150 °C at a depth of 2500 m can be obtained for a fault zone permeability of 1.6 × 10−14 m2. Based on a multi-disciplinary approach, this work establishes a potential predictive tool for future high-temperature geothermal operations within basement rocks hosting large-scale fault systems.

中文翻译：

---

关于地壳断层带的地热潜力：以蓬蒂鲍德地区为例（法国法国中部地块）

本研究旨在了解一种新型的高温热发电地热系统的潜力：地壳断层带（CFZ）。根据地质和地球物理数据，庞蒂鲍德断层带（法国地块中部）被怀疑在几公里深度处拥有活跃的热液系统。断层带的深层几何形状和渗透率分布是评估蓬吉鲍德站点地热潜力所需的主要未知参数。结构和薄层观测，实验室渗透率和连通孔隙率测量以及X射线显微断层扫描观测表明，热液系统的行为类似于双重基质裂缝渗透率储层。进行了数值模拟，其中我们改变了断层倾角和断层带渗透率与基岩R之比。结果表明，可以确定三种主要的对流方式（弱对流，单细胞对流和双细胞对流）。对于足够高的断层带渗透率（> 1×10-15 m2），浮力驱动的流动在2-5 km的深度处会产生数十°C的正热异常。对于垂直断层带，R值越高，热异常越大。然后，将数值模型应用于受地质约束的庞吉鲍德断层带，结果表明，对于断层带渗透率1.6×10-14 m2，可以在2500 m的深度处获得150°C的温度。基于多学科方法，