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    陕西省华阴-华州地区干热岩资源热源机制研究及开采潜力评价

    • 摘要: 干热岩资源具有清洁环保、储量丰富、稳定性好等优点,科学开发利用干热岩资源有助于我国双碳战略目标的实现。陕西省关中盆地是一个典型的中低温地热田,其中华阴华州地区具备良好的地热地质条件,是潜在的干热岩勘查有利地段。在收集整理研究区地热地质资料基础上,通过地热地质调查、地球物理勘探、样品采集测试等手段,基本查明了研究区干热岩分布范围及储层、盖层的结构特征,分析了岩石圈热结构特征和热源机理,研究了热流格局形成机制,评价了资源潜力。主要结果表明:(1)研究区干热岩资源类型属于典型的沉积盆地型,主要源自地幔底辟上涌、岩石圈减薄拉张导致的较高地幔热流,其次为地壳岩石放射性元素衰变热。在莫霍面隆起、岩石圈明显减薄造成的高热流背景下,浅部地层导热系数横向不均一,太古界太华群花岗岩导热系数高,新生界砂岩、含砾砂岩、泥岩导热系数小,引起热流重新分配,在基底隆起区再汇聚是区内干热岩主要成热机制。(2)研究区地温梯度为22.2~36.5℃/km,平均为33.0±2.0℃/km,大地热流为53.7~89.2 mW/m2,平均为80.3±4.9 mW/m2,地温梯度和大地热流由西向东均呈高-低-高-低的变化趋势。(3)沉积层底界热流为45.5~86.8 mW/m2,平均值为75.5±5.3 mW/m2;上地壳底界热流为29.2~62.5 mW/m2,平均值为54.5±4.8 mW/m2;中地壳底界热流为17.1~50.0 mW/m2,平均值为42.2±4.9 mW/m2;下地壳底界热流为15.3~48.1 mW/m2,平均值为40.4±4.9 mW/m2。(4)研究区壳幔热流比为0.85~2.52,中部壳幔热流比小于1,面积占比为67%。莫霍面温度为496.8~845.9℃,平均温度为768.6±52.5℃,莫霍面温度在西北角及中部最高,在东北角最低。(5)评价了研究区8km埋深范围内干热岩(≥150℃)地热资源量。深部地层温度为150℃时对应的地层深度为3.5~6.3 km,8km深度对应温度为182.7~260.6℃。干热岩地热资源总储量为46.1 EJ,折合标煤262, 631万吨,按照回收率2%计算,可开采资源储量为0.92EJ,折合标煤5253万吨。本文通过分析华阴华州地区干热岩的热源机制及资源潜力,为今后干热岩资源的科学利用与热源供给可持续性评价提供理论依据。

       

      Abstract: Dry hot rock resources have advantages such as clean environmental protection, abundant reserves, and good stability. The scientific development and utilization of dry hot rock can help achieve China's dual carbon strategy goals. The Guanzhong Basin in Shaanxi Province is a typical low-temperature geothermal field, and the Huayin Huazhou area has good geothermal geological conditions, making it a potential favorable area for dry hot rock exploration. On the basis of collecting and organizing geothermal geological data in the study area, this article has basically identified the distribution range of dry hot rocks and the structural characteristics of reservoirs and caprocks in the study area through geothermal geological surveys, geophysical exploration, sample collection and testing, analyzed the thermal structure characteristics and heat source mechanism of the lithosphere, studied the formation mechanism of heat flow patterns, and evaluated resource potential.The main results : (1) The type of dry hot rock resources in the study area is a typical sedimentary basin type, and the heat mainly comes from the higher mantle heat flow caused by the upwelling of the mantle diapir and the thinning and stretching of the lithosphere, followed by the decay heat of radioactive elements in crustal rocks. Under the background of high heat flow caused by Moho uplift and significant thinning of the lithosphere, the thermal conductivity of shallow strata is laterally uneven. The thermal conductivity of the Taihua Group granite in the Archean is high, while the thermal conductivity of the Cenozoic sandstone, gravel bearing sandstone, and mudstone is low, causing redistribution of heat flow. The re convergence in the basement uplift area is the main heating mechanism of dry hot rocks in the area. (2) The geothermal gradient in the study area is 22.2-36.5 ℃/km, with an average of 33.0 ± 2.0 ℃/km. The geothermal heat flow is 53.7-89.2 mW/m2, with an average of 80.3 ± 4.9 mW/m2. The geothermal gradient and geothermal heat flow show a trend of high low high low from west to east. (3) The heat flux at the bottom boundary of the sedimentary layer is 45.5~86.8 mW/m2, with an average value of 75.5 ± 5.3 mW/m2; The heat flux at the bottom boundary of the upper crust is 29.2~62.5 mW/m2, with an average value of 54.5 ± 4.8 mW/m2; The heat flux at the bottom of the middle crust is 17.1-50.0 mW/m2, with an average value of 42.2 ± 4.9 mW/m2; The heat flux at the bottom of the lower crust is 15.3~48.1 mW/m2, with an average value of 40.4 ± 4.9 mW/m2. (4) The heat flux ratio between the crust and mantle in the study area is 0.85-2.52, and the heat flux ratio between the middle crust and mantle is less than 1, accounting for 67% of the area. The Moho surface temperature ranges from 496.8 to 845.9 ℃, with an average temperature of 768.6 ± 52.5 ℃. The Moho surface temperature is highest in the northwest and central corners, and lowest in the northeast corner. (5) Calculated the geothermal resources of hot dry rocks (≥ 150 ℃) within a depth range of 8km in the study area. When the temperature of the deep formation is 150 ℃, the corresponding depth of the formation is 3.5-6.3 km, and the temperature at a depth of 8 km is 182.7-260.6 ℃. The total reserve of geothermal resources in dry hot rock is 46.1 EJ, equivalent to 2626.31 million tons of standard coal. Calculated based on a recovery rate of 2%, the exploitable resource reserve is 0.92 EJ, equivalent to 52.53 million tons of standard coal. This article analyzes the heat source mechanism and resource potential of dry hot rocks in the Huayin Huazhou area, providing a theoretical basis for the scientific utilization of dry hot rock resources and the sustainable evaluation of heat source supply in the future.

       

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