渭河盆地大地热流测量与地热系统热源机理研究

As the local renewable energy, geothermal energy has many advantages, such as large amount of resources, high efficiency, low cost, good effect of energy saving and emission reduction. Therefore, geothermal energy is considered to be one of the most important alternative energy for the future of human beings. Heat source analysis is one of the basic contents on the formation mechanism of geothermal system. The basic method to analyze the heat source of the geothermal system is by the terrestrial heat flow measurement and lithospheric thermal structure calculation. A variety of geological and geophysical data show that the Weihe basin is a passive rift, which means that there must be differences in heat source mechanism of geothermal system between the Weihe basin and other active rifts. Accordingly, the thermal genetic model of the geothermal system in the Weihe basin, which was based on the active rift basin, also needs to be reestablished. The purpose of this project is to study the geothermal field and the lithospheric thermal structure of the Weihe basin on the basis of the temperature logging and the thermal physical properties measurement. Then, on the base of the thermal anomaly distribution and tectonic division of hydrogeological conditions, geothermal systems will be divided and heat source mechanism (heat source composition and tectonic-thermal channel) of representative geothermal systems will be analyzed. Finally, the geothermal resources potential in Weihe basin will be carried out and the heat source model of geothermal system in passive rifts will be build. The result of the project will lay the foundation for sustainable exploration and development and help realize the goal of geothermal resources development and utilization in the "13th Five-Year" planning in Shanxi province.

作为地球的本土可再生能源，地热能具有资源量大、利用效率高、成本低、节能减排效果好等诸多优点，是人类未来的重要替代新能源之一。热源解析是地热系统形成机理研究的基本内容之一，其基本方法是开展大地热流测量与岩石圈热结构精细研究。多种地质、地球物理资料表明，渭河盆地为被动裂谷盆地，其地热系统热源机理与主动裂谷盆地必定存在差异，而传统建立在主动裂谷盆地基础之上的渭河盆地地热系统热成因模式亦需要重新建立。本项目拟在深井稳态地温测量和岩石热物性测试基础上，开展渭河盆地地温场和岩石圈热结构精细研究，进而根据热异常分布及构造-水文地质条件，划分地热系统，解析代表性地热系统的热源机理——热源构成与构造-热通道，建立被动裂谷盆地地热系统的热源模式，评价渭河盆地典型地热系统地热资源潜力，为研究区地热资源的可持续勘探开发提供合理建议，助力渭河盆地地热资源开发利用“十三五”规划目标顺利实现。

渭河盆地地热资源极其丰富，发育多个大型整装地热田，资源量大、水温高、水质优良、易于开采。本项目在深井稳态地温测量和岩石热物性测试基础上，开展渭河盆地地温场和岩石圈热结构精细研究，进而根据热异常分布及构造-水文地质条件，划分地热系统，解析地热系统的热源机理，建立被动裂谷盆地地热系统的热源模式，评价渭河盆地典型地热系统地热资源潜力。.研究认为，咸阳地热田属于以传导为主的沉积盆地型地热田，但与典型的传导型地热田相比，咸阳地热田的地温场特征又存在特殊性，表现为钻孔温度—深度曲线分段性明显。测温资料揭示了咸阳地热田水动力系统在垂向上存在多层结构：浅部为垂向重力驱动型，中上部为正常压实型，中下部为侧向重力驱动型，下部为封闭型。渭河盆地现今大地热流值分布范围为62.5~80.2mW/m2，平均为70.8±4.8mW/m2，西部明显高于东部，西安坳陷陷最高，咸礼凸起次之；渭河断裂并不是控热断裂，其沟通作用引起的水热循环一定程度上影响了浅部热量再分配，对渭河盆地地温场并没有起到明显的控制作用。渭河盆地与鄂尔多斯盆地的壳/幔热流比类似，为典型的“温壳温幔”，符合被动裂谷的热结构特征。综合渭河盆地多种地质、地球物理资料，论证了渭河盆地为被动伸展裂陷模式。从华北裂谷、山西裂谷到渭河裂谷，伸展裂陷模式经历了从主动到被动的有序变化，表明太平洋板块俯冲引起的深部热扰动在华北地块东部和西部存在明显差异，同时暗示了华北克拉通破坏的序列性。综合分析渭河盆地地质—地球物理资料认为，岩石圈表层伸展破裂、深部重力均衡调整进而引起软流圈被动上涌，其产生的相对高地幔热流的热传导和深大断裂沟通的水体热对流相互叠加作用，共同构成了渭河盆地中—低温地热田的热源机理。研究成果为渭河盆地地热资源的可持续勘探开发提供重要科学依据。