Characteristics And Development Of Geothermal Resources In The Middle And Deep Layers Of The Weihe Basin

The Weihe Basin is sandwiched between the Ordos block and the Qinling orogenic belt.The area is affected by four giant tectonic systems.The deep activities are intense and the geothermal resources in the area are extremely rich.The geothermal development of the basin has a long history.Up to now,the degree of development and utilization varies greatly among regions.In some areas,there are phenomena such as direct discharge without recharge,waste of geothermal resources,and excessive decline of water heads in local areas.Therefore,on the basis of the study of geothermal field and geothermal resources in the Weihe Basin,it is especially important that how to develop and utilize geothermal resources more green,scientifically and efficiently,and establish a reasonable geothermal development model for sustainable mining.This paper chooses the middle-deep geothermal resources in the Weihe Basin as the research object.Based on the analysis of the deep tectonic thermal background of the basin,and understanding deep structural features and thermal dynamics,discussed the deep background of the geothermal field in the Weihe Basin.Combining regional tectonic features,deep thermal structure,shallow reservoir conditions,basin geothermal field characteristics and geothermal resource distribution,summarized the enrichment rule of geothermal resources in the basin,preliminarily divided the favorable areas of geothermal resources,and improved the formation mechanism and mode of geothermal field in the basin.It provides partial theoretical support for the subsequent development and utilization of the basin.The Moho in the Weihe Basin has a large uplift,the thickness of the lithosphere is generally thinned,and the deep thermal activities are strong.The basin transmits heat through two ways:heat conduction and fault convection.Based on the analysis of a large number of formation temperature data,the average geothermal gradient of the Weihe Basin is determined to be3.49°C/100 m.The average geothermal gradient and heat flow value of the Xi'an Sag and Gushi Sag are higher.The geothermal gradients are 3.85 and 3.62°C/100 m,respectively,higher than the Ordos Basin,the geothermal anomaly is obvious.The vertical variation law of geothermal temperature of each tectonic unit in the Weihe Basin is summarized.The ground temperature of the basin is 40⁶0°C,65-95°C,80-135°C and 115¹75°C at 1000m,2000m,3000m and4000m depth respectively.The geothermal distribution in Xi'an and Gushi depressions is higher at different depths.Based on the analysis of different lithology thermal conductivity tests,the relationship between thermal conductivity and depth of different lithologic rocks in the basin is established.Generally,with the increase of depth,the law of thermal conductivity gradually increases.The thermal conductivity of mudstone is the lowest,the thermal conductivity of sandstone is middle,and the thermal conductivity of dolomite is the largest.The calculated total heat of the Weihe Basin is 269×10¹⁶kcal,and the standard coal is3384.84×10⁸t.The vertical difference in the amount of resources in different horizons is obvious.The Lantian-Bahe Formation and Gaoling Group are the most abundant,while the Xi'an Sag and Gushi Sag are the most abundant in the plane,which is a favorable area for geothermal development.The geothermal field in the Weihe Basin is mainly caused by the conduction of the mantle heat flow and the channel provided by the deep thermal-controlled thermal fault,and is formed by the combination of basin structure,reservoir and other factors.In view of the status quo and existing problems of geothermal development in the Weihe Basin,suggestions for geothermal development are proposed.