| Summary: | In order to explore the characteristics of karst reservoir and the genetic mechanism of the Nanle geothemal field in Bohai Bay Basin.Based on geophysical and geological data, this paper analyzes the factors of the geothermal field that include karstic reservoir distribution, hydro-chemical characteristics, migration channels and geothermal, and eventually we construct the conceptual model of the geothermal field. The results show that there are four stages of Ordovician weathering crust karst heat reservoirs in the Nanle geothermal field, including Caledonian, Indo-Hercynian, Yanshan and Xishan. The burial depth of the Ordovician karstic reservoir is 1 427-2 135 m (effective thickness: 46.2-91.7 m). The reservoir is characterized by good caprock and geothermal gradient (3.04-3.24℃/hm), and the groundwater is SO4+Cl-Na+Ca-B type. It is considered that the geothermal field is a conductive one, which was formed in the west slope belt of Dongpu Sag-intracontinental basin in the high heat flow. And the system is characterized by the cold water that deep into the bedrock of cycle that influenced by thermal refraction and redistribution effect of heat flow and friction heat generation of Lanliao fault, which along the regional unconformity and fracture migration, enrichment, whose recharged water source comes from atmospheric precipitation in the Taihangshan and Luxinan, and finally concentrated in Ordovician karst heat reservoir of the Nanle Sub-uplift. The total extractable geothermal resource of the Ordovician karstic reservoir in the Nanle Sub-uplift geothermal field is 1.02×109 GJ (3.5×107 t standard coal eqv.), and the annual geothermal resource can meet the indoor heating demand of 0.124 million square meter. The geothermal field has a good market potential.The results have a good guiding significance for the development and utilization of karst reservoirs in the south of Bohai Bay Basin-Nanle geothermal field.
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