地热系统地质要素地球化学识别方法与应用以广东省惠州市石坝盆地为例

    A geochemical method for identifying geological elements of geothermal systems and its application: A case study of the Shiba Basin, Huizhou City, Guangdong Province

    • 摘要: 地热系统有“源、通、盖、储”4个地质要素,目前主要依据物探、地震、地质成果来识别和解析。地热系统引起的地球物理、地球化学效应导致各地质要素都可以在地表形成地球化学异常。本文以石坝盆地地热系统为勘探实例,参照邻区黄沙洞地热田的地球化学特征,结合地热地质条件、指标的来源及物理化学性质特征,优选出 “源、通、盖、储”地质要素的识别指标,探索建立了对应的识别方法。结果显示:石坝盆地地热系统的热源为壳幔混源,幔源热贡献率为54.42%、壳源热贡献率为45.58%;热储存在3种供热方式:河源深大断裂传热、花岗岩放射性生热、侵入岩传热;水源主要为大气降水,降水通过河源深大断裂和紫金—博罗大断裂给有利区补水。根据该方法,石坝盆地识别出3个地热有利区,预测这3个有利区平均盖层厚度为2 629 m,平均热储温度为167 ℃,热储类型为水热—干热岩组合高温地热系统。

       

      Abstract: A geothermal system is composed of four geological elements: sources, pathways, cap rocks, and reservoirs. Currently, these elements are primarily identified and analyzed based on geophysical, seismic, and geological results. The geophysical and geochemical effects induced by geothermal systems can lead to the formation of geochemical anomalies of these elements on the surface. This study investigated the geothermal system in the Shiba Basin, Huizhou City, Guangdong Province. By referring to the geochemical characteristics of the neighboring Huangshadong geothermal field and combining the geothermal geological conditions, sources of various indicators, and physicochemical properties, this study selected the optimal indicators for identifying the four geological elements mentioned above. Accordingly, a corresponding geochemical identification method was developed. The results indicate that the geothermal system in the Shiba Basin has a heat source of a mixed crust-mantle source, with mantle- and crust-derived heat accounting for 54.42% and 45.58%, respectively. The geothermal reservoirs exhibit three heat supply modes: heat transfer via the Heyuan deep-seated fault, radioactive heat generation by granites, and heat transfer via intrusions. Meteoric water serves as the primary water source, recharging geothermal play fairways through the Heyuan and Zijin-Boluo deep-seated faults. Using the proposed geochemical identification method, three geothermal play fairways have been identified in the Shiba Basin. They are predicted to have an average cap rock thickness of 2 629 m and an average reservoir temperature of 167 ℃, identified as composite hydrothermal-hot dry rock (HDR) high-temperature geothermal systems.

       

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