Structural characteristics of geothermal reservoirs in southwest Guizhou:Taking Pingdong geothermal reservoir in Wangmo county as an example
As future advantageous resources as well as renewable energy sources,geothermal resources are widely distributed and used due to their large reserves.They are also clean,environmental and recyclable.Therefore,the development and utilization of geothermal resources has become an important means of global energy transformation and mitigation of global warming.In this context,understanding the dynamics of geothermal fluid movement and the distribution characteristics of geothermal resources in the study area becomes important before the development of these resources.Such knowledge is essential for harnessing the full potential of geothermal energy in the area under consideration.The development of geothermal resources based on geothermal temperature gradients is controlled by regional geothermal reservoir structures and water-conducting structures.In order to gain a deeper understanding of the circulation mechanism of the geothermal fluids in the study area,this study takes Pingdong geothermal reservoir in Wangmo county of Guizhou Province as the research object,and analyzes the lithological characteristics,thermal reservoir structures,water-conducting structures,characteristics of geothermal fields,and hydrochemical characteristics of geothermal fluids in this area on the basis of the geological survey and the structural characteristics of geothermal reservoir exposed by ZK1 borehole.The results show that the study area is located at a national key metallogenic zone—the Youjiang rift of Jiangnan composite orogenic belt at the north of Youjiang metallogenic zone,i.e.Shangli geoanticlinal inclined end of the combination part of NW Wangmo fold belt in the foreland basin and the deformation area of EW Ceheng closed fold.The tectonic stress is concentrated in this area.Geothermal fluids in the study area receive atmospheric precipitation and are replenished along the distribution area of carbonate rock in the core of the Shangli geoanticline on the northwest side.Then they fall into deep circulation along the fissure and fracture zones and converge in the geothermal reservoir(from the reef limestone to the limestone of Houziguan Formation)and in the fault-fracture zone of western Wangmocheng.After the interaction with the surrounding rocks,the geothermal fluids carry out the deep circulation from northwest to southeast,during which they continuously absorb the heat flow transmitted upward from the deep part of the earth's crust through deep faults.The heated and upwelling geothermal fluids move upward due to the buoyancy produced by volume expansion(decreasing density).The fluids at low temperature in the upper part move under gravity due to high density,forming a deep circulation system of the geothermal water in this area.Geothermal fluids in the study area are enriched in the fault-fracture zone of western Wangmocheng and in the combination part of the Permian reef limestone and the limestone of Houziguan Formation in the thermal reservoir.The runoff process of geothermal fluid is mainly affected by the fault structure.The recharge,runoff and discharge conditions of underground geothermal water in the study area generally follow the hydrogeological conditions of deep circulation.The geothermal resources in the study area show typical convective characteristics of folds,uplifts and faults.The analysis of Piper's three-line diagram shows that the hydrochemical type of geothermal fluids and shallow groundwater in the study area is HCO3-Ca-Mg type,which is mainly controlled by carbonate minerals in thermal storage aquifers(Pjh and P2h).The warming process of geothermal fluid is mainly controlled by the geothermal temperature gradient,with the average of 2.34℃·(100m)-1.The thermal storage structure and water-conducting structure also have a certain influence on the warming contribution.This research contributes significantly to our comprehension and prediction of the movement patterns of geothermal fluids and the distribution traits of geothermal resources.As a result,it offers invaluable reference for the development of geothermal energy in other analogous geothermal reservoirs within Southwest Guizhou.
thermal reservoirgeothermal gradientstructural featurePingdong geothermal system in Wangmo county
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