The thermal structure and temporal evolution of high-enthalpy geothermal systems
The thermal structure and temporal evolution of high-enthalpy geothermal systems
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DOI：
10.1016/j.geothermics.2016.02.004
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发表时间：
2016-07
期刊：
影响因子：
3.9
通讯作者：
S. Scott;T. Driesner;P. Weis
中科院分区：
文献类型：
--
作者：
S. Scott;T. Driesner;P. Weis
数值模拟是研究高焓地热系统对生产响应的有力工具，但很少有人研究这些系统的长期演化和热结构。本文报道了一系列岩浆侵入体周围流体流动和热传递的数值模拟，揭示了高焓地热系统的自然热和水力结构的关键特征。我们探讨了关键的地质控制，如围岩渗透率、侵入体的侵位深度和几何形状以及侵入体附近随温度变化的渗透率，对沸腾带的深度和范围、上行流羽流的数量和空间形态的影响，以及这些方面是如何在系统寿命内演变的。主岩渗透率是对沸腾带的总体结构、温度分布和范围的主要控制，因为高渗透率(≥10−14m2)系统显示浅沸腾带限制在≤1公里深以内，而中等渗透率(∼10−15m2)系统显示垂直扩展的沸腾带从地表延伸到侵入体。侵位深度是进一步的控制，因为在≥3公里深的侵入驱动的中等渗透率系统只显示1公里以上的沸腾。如果冷却入侵在显著超过水的临界温度时变得可渗透，则上行流的热焓变得足够高，使得高渗透率的系统在垂直方向上显示扩展沸腾区，而中等渗透率系统在入侵附近显示空间扩展的超临界水区域。单一侵入体上方多股空间分离的上升流羽流的发展是高渗透率和深部侵位深度系统的特征。根据主要的地质控制，系统在相对于侵入热源的压力、温度和热焓方面表现出特有的横向和垂直梯度，这可能有助于地热勘探和野外测量解释。
Numerical modeling is a powerful tool to investigate the response of high-enthalpy geothermal systems to production, yet few studies have examined the long-term evolution and thermal structure of these systems. Here we report a series of numerical simulations of fluid flow and heat transfer around magmatic intrusions which reveal key features of the natural thermal and hydraulic structures of high-enthalpy geothermal systems. We explore the effect of key geologic controls, such as host rock permeability, the emplacement depth and geometry of the intrusion, and temperature-dependent permeability near the intrusion, on the depth and extent of boiling zones, the number and spatial configuration of upflow plumes, and how these aspects evolve over the systems’ lifetime. Host rock permeability is a primary control on the general structure, temperature distribution and extent of boiling zones, as systems with high permeability (≥10−14m2) show shallow boiling zones restricted to ≤1 km depth, while intermediate permeability (∼10−15m2) systems display vertically extensive boiling zones reaching from the surface to the intrusion. Intrusion emplacement depth is a further control, as intermediate permeability systems driven by an intrusion at ≥3 km depth only show boiling above 1 km. If a cooling intrusion becomes permeable at temperatures significantly in excess of the critical temperature of water, the enthalpy of the upflow becomes high enough that systems with high permeability show vertically extensive boiling zones, and intermediate permeability systems spatially extensive zones of supercritical water near the intrusion. The development of multiple, spatially separated upflow plumes above a single intrusive body is characteristic of systems with high permeability and deep emplacement depth. Depending on the primary geologic controls, systems exhibit characteristic lateral and vertical gradients in pressure, temperature and enthalpy relative to the intrusive heat source which may aid in geothermal exploration and interpretation of field measurements.