Accumulation Mechanism Of Geothermal Resources In Karst Thermal Reservoir In Xiong’an New Area

The carbonate karst thermal reservoir in Xiong’an area has significant development potential.Clarifying accumulation mechanism can contribute to the sustainable development and utilization of geothermal resources.In this paper,based on previous research results and measured physical parameters,the accumulation mechanism of geothermal resources in karst thermal reservoir has been analyzed.The formation of karst and fractures in the Wumishanzu formation is closely related to tectonic uplift,especially in the Yanshan and Himalayan period.The karst fractures with good transmissibility are mostly developed at this time,distributing as layers in the vertical.The thickness of fracture zone averages 4.70 m and the total fracture zone thickness accounts for 41.9% of the reservoir thickness.There are a large number of fractures having good connectivity due to their semi-filled and unfilled interstices.Thermal conductivities of 96 core samples from 34 boreholes in research area have been measured and the thermal conductivities of dolomite and sandstone average 4.95±1.19 W/(m·K)and 1.80±0.44 W/(m·K),respectively.The fracture mesh model established by joint fractures distribution is used for numerical simulation coupling groundwater movement and heat transfer.Results show that the superposition of the thermal convection in fracture fluid and the thermal conduction in rocks with high thermal conductivities are the conditions for the formation of high temperature area.Then the Niutuozhen geothermal field model and Xiong’an new area model have been built,showing that heat flow from deep depth prefers to accumulate in uplift area.In consideration of many factors including the geological structure,heat source,heat transfer ability,fault,reservoir,groundwater movement and cover layer,the accumulation mechanism of geothermal resources in karst thermal reservoir in Xiong’an new area has been established.The precipitation migrates from Taihang mountain and Yanshan mountain to the bottom of the research area through the deep fault zone,and was heated by the high heat flow during migration process.When the groundwater carrying heat encounters the impermeable faults,it moves upward along the faults and fractures,forming a high-temperature geothermal area in the top of the uplift which is covered by a cover layer.