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Geothermal Reservoir Characteristics and Geothermal Resource Evaluation of Mesoproterozoic Wumishan Formation In Xiong'An New Area, China
In order to deepen the large-scale development and utilization of the middle and deep geothermal resources in Xiong’an New Area, based on the outcrop, core, rock slice, drilling data and seismic line interpretation results, the buried depth, thickness, petrology and reservoir space characteristics of the thermal reservoir of Wumishan Formation of Jixian System in the Mesoproterozoic are analyzed, the thermal reservoir sedimentary microfacies model is established, and the fault distribution, porosity, permeability distribution characteristics and diagenesis controlling karst development factors are studied. The characteristics of karst thermal reservoir and caprock, geothermal gradient and hydrodynamic conditions of Wumishan Formation are clarified, the geothermal resource accumulation model in this area is established, and the favorable exploration target area of Wumishan Formation thermal reservoir is optimized. Finally, geothermal water reserve and recoverable geothermal water amount in the reservoir of Wumishan Formation with the roof buried no more than 5000m both in Xiong’an New Area and in the main construction of Xiong’an New Area are evaluated. The research results show that the Wumishan Formation in Xiong’an New Area is the main geothermal reservoir at present. The geothermal resources of this formation are a large-scale conductive hot water storage system enriched in the Rise belts under the normal heat flow background, with atmospheric precipitation as the water source, weathered crust karst and deep faults as the migration channels, mainly through the long-distance supply of Taihang Mountain and Yanshan mountain. The wellhead water temperature of Wumishan Formation thermal reservoir is generally 57 ℃ ~ 83 ℃, up to 109 ℃, the water flow is generally 80 ~ 120 m^3/h, and the mineralization is 1900 ~ 3100 mg/L; The buried depth of thermal reservoir is relatively shallow in Rongcheng Rise and Nutuozhen Rise, with a roof of 700m ~ 2600m and a thickness of 800m ~ 1400m; In Gaoyang low Rise, the depth is relatively deep, the roof is generally 3000m ~ 4000m, the thickness is generally 700m ~ 1000m, and the temperature is relatively Rise. The thickness of the caprock is generally greater than 700m, and the geothermal gradient is between 3 ℃ ~ 8 ℃/100m in the Rise areas. The lithology is mainly dolomite, and the sedimentary microfacies are characterized by the development of dolomite tidal flat and algae dolomite tidal flat, which are easy to develop various dissolution and fractures; The karst development period is mainly Early Yanshanian - Himalayanian; 61.3% of the porosity is between 1% and 6%, and 87.8% of the permeability is between 0.01 and 100mD. The thermal reservoir of Wumishan Formation can be divided into the most favorable area, the second favorable area, the third favorable area, the general favorable area and the unfavorable area, according to the structural development, the porosity and permeability properties, the geothermal gradient, the buried depth of the top surface and the sedimentary microfactors, etc. For the Wumishan Formation thermal reservoir with the roof buried no more than 5000m, according to the principle that the recoverable geothermal water in 100 years accounts for 50% of the total storage water reserve, the recoverable geothermal water is 142.68×10^8 m^3, which content recoverable heat 33.25×10^8 GJ, converted into standard coal 1.136×10^8 t；Among them, the recoverable geothermal water in the main construction area of Xiong’an New Area is 42.476×10^8 m^3 , the heat content of recoverable geothermal water is 7.928×10^8 GJ, equivalent to standard coal 0.2708×10^8t , the annual heating area can meet accounting for 30.1% to 48.6% of the actual demand . The geothermal resource endowment of Wumishan Formation in Xiong’an New Area is very good, which could not meet the actual energy demand of the main construction area alone.