青海共和盆地干热岩赋存地质特征及开发潜力

OCCURRENCE GEOLOGICAL CHARACTERISTICS AND DEVELOPMENT POTENTIAL OF HOT DRY ROCKS IN QINGHAI GONGHE BASIN

青海共和盆地贮藏有丰富的干热岩地热资源。为提升共和盆地干热岩地热资源成因的理论认识,进一步推动干热岩资源的勘探,文章从共和盆地干热岩热源机制、盖层条件、储层特征等方面对共和盆地干热岩资源成因件进行了全面分析。首先,结合区域地质构造分析、地热地质调查、地球物理(航磁、地震)解译等手段,在共和盆地恰卜恰岩体内实施了4口深度为2927~3705 m的干热岩勘查孔,并在3705 m处钻获236 ℃的优质干热岩资源,为中国非现代火山区干热岩地热资源勘探的首个重大突破。其次,系统测试了钻孔不同深度花岗岩放射性,结果表明,共和盆地花岗岩体铀、钍、钾放射性含量略高于大地背景值,放射性生热率较低,对干热岩热源的贡献小,其热源可能来自壳内熔融体。第三,基于地质资料分析和航磁解译,圈定了共和盆地总体面积约1.4×10 4 km 2的潜在干热岩分布区。最后,采用体积法评估了共和盆地干热岩资源潜力,结果表明,共和盆地3.0~6.0 km深度范围保守的、静态干热岩资源总量为8974.74×10 18 J,换算标准煤可达3066.19×10 8 t,具有广阔的开发利用前景。

The Gonghe Basin is rich in hot dry rock geothermal resources. In order to enhance the theoretical understanding of the genesis of hot dry rock geothermal resources in the Gonghe Basin and further promote the exploration of hot dry rock resources, a comprehensive analysis of the genesis of hot dry rock resources in the Gonghe Basin is made from the heat source mechanism, caprock conditions and reservoir characteristics. Firstly, combined with regional geological structure analysis, geothermal geological survey, geophysical (aeromagnetic, earthquake) interpretation, four hot dry rock exploration wells with the depth of 2927-3705 m were drilled in the Gonghe Basin. At 3705 m, the high-quality hot dry rock resources of 236 ℃ were obtained, which was the first major breakthrough in the exploration of hot dry rock geothermal resources in China’ s non-modern volcanic areas. Secondly, radioactivities of granites from different depths were tested. The results show that the radioactive elements content of U, Th and K in the granitoids of the Gonghe Basin is slightly higher than the background value of the earth, and the radioactive heat generation rate is relatively low, the contribution of radioactive heat to the heat source of hot dry rock is less and the heat source may come from the melt in the Crust. Thirdly, based on geological data analysis and aeromagnetic interpretation, the potential hot dry rock distribution area of the Gonghe Basin is about 1.4×10 4 km 2. Finally, the volumetric method is used to evaluate the potential of hot dry rock resources in the Gonghe Basin. The results show that the total conservative and static amount of hot dry rock resources in the 3.0-6.0 km range of the Gonghe Basin is 8974.74×10 18 J, and the converted standard coal can reach 306.619 billion tons, showing the broad prospects for development and utilization.