In the first kilometers of the subsurface, temperature anomalies due to heat conduction processes rarely exceed 20–30 ^∘C. When fault zones are sufficiently permeable, fluid flow may lead to much larger thermal anomalies, as evidenced by the emergence of thermal springs or by fault-related geothermal reservoirs. Hydrothermal convection triggered by buoyancy effects creates thermal anomalies whose morphology and amplitude are not well known, especially when depth- and time-dependent permeability is considered. Exploitation of shallow thermal anomalies for heat and power production partly depends on the volume and temperature of the hydrothermal reservoir. This study presents a non-exhaustive numerical investigation of fluid flow models within and around simplified fault zones, wherein realistic fluid and rock properties are accounted for, as are appropriate boundary conditions. 2D simplified models point out relevant physical mechanisms for geological problems, such as “thermal inheritance” or pulsating plumes. When permeability is increased, the classic “finger-like” upwellings evolve towards a “bulb-like” geometry, resulting in a large volume of hot fluid at shallow depth. In simplified 3D models wherein the fault zone dip angle and fault zone thickness are varied, the anomalously hot reservoir exhibits a kilometer-sized “hot air balloon” morphology or, when permeability is depth-dependent, a “funnel-shaped” geometry. For thick faults, the number of thermal anomalies increases but not the amplitude. The largest amplitude (up to 80–90 ^∘C) is obtained for vertical fault zones. At the top of a vertical, 100 m wide fault zone, temperature anomalies greater than 30 ^∘C may extend laterally over more than 1 km from the fault boundary. These preliminary results should motivate further geothermal investigations of more elaborated models wherein topography and fault intersections would be accounted for.

中文翻译：

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断层区内外的浮力驱动流动引起的2D和3D热异常的形态和幅度

在地下的前几公里，由于热传导过程引起的温度异常很少超过 ^20–30∘C.当断层带具有足够的渗透性时，流体流动可能导致更大的热异常，这可以通过温泉的出现或与断层有关的地热储层来证明。由浮力作用触发的热液对流会产生热异常，其形态和振幅尚不为人所知，尤其是在考虑到与深度和时间有关的渗透率时。浅层热异常用于热力发电的开发部分取决于热液储层的体积和温度。这项研究提出了简化断层带内和周围的流体模型的非穷举性数值研究，其中考虑了实际的流体和岩石特性以及适当的边界条件。2D简化模型指出了地质问题的相关物理机制，例如“热继承”或脉动羽状流。当渗透率增加时，经典的“手指状”上升流将演变为“球状”几何形状，从而在浅深度产生大量热流体。在断层带倾角和断层带厚度变化的简化3D模型中，异常热储层呈现出千米大小的“热气球”形态，或者当渗透率与深度相关时，呈现出“漏斗形”几何形状。对于较厚的断层，热异常的数量会增加，但幅度不会增加。最大振幅（高达80–90 在断层带倾角和断层带厚度变化的简化3D模型中，异常热储层呈现出千米大小的“热气球”形态，或者当渗透率与深度相关时，呈现出“漏斗形”几何形状。对于较厚的断层，热异常的数量会增加，但幅度不会增加。最大振幅（高达80–90 在断层带倾角和断层带厚度变化的简化3D模型中，异常热储层呈现出千米大小的“热气球”形态，或者当渗透率与深度相关时，呈现出“漏斗形”几何形状。对于较厚的断层，热异常的数量会增加，但幅度不会增加。最大振幅（高达80–90 ^∘ C）是用于垂直断裂带获得。在一个垂直的顶部，百米宽断裂带，大于30的温度异常 ^∘ C可以横向地在多于从故障边界1公里延伸。这些初步的结果将促使人们对更精细的模型进行进一步的地热研究，其中将考虑地形和断层的交叉。