Exploring the occurrence characteristics of geothermal resources in the Nangong geothermal field based on the magnetotelluric method
LU Xing-Chen1,2(), XING Qian1(), XU Yong2, LYU Guo-Sen3, CHEN Xiang-Zhong4, WANG Rui-Xing4, HUANG Shen-Shuo4
1. Sinopec Star Petroleum Co.,Ltd.,Beijing 100083,China 2. Sinopec Green Energy Geothermal Development Co.,Ltd.,Xiong'an 071800,China 3. School of Environmental Studies,China University of Geosciences(Wuhan),Wuhan 430074,China 4. Beijing Judeng Geological Exploration Technology Co.,Ltd.,Beijing 102299,China
To clarify the occurrence characteristics of geothermal resources in the Nangong geothermal field,this study revealed the subsurface strata and structures in the geothermal field using the magnetotelluric(MT) method in combination with drilling and geologic data.Furthermore,this study systematically analyzed the distributions of shallow and deep geothermal resources and elucidated the heat source mechanisms.Finally,this study constructed the geological model of the Nangong geothermal field.The results show that within a depth of 4000 m,the strata in the Nangong geothermal field comprise the Quaternary,Neogene,Paleogene,Permian,Carboniferous,Ordovician,and Cambrian strata from top to bottom.On the east side of the urban area of Nangong City, there are two concealed NE-trending normal faults(i.e.,F1 and F2),exhibiting a NW dip direction and steep dip angles.The fault-affected zone displays well-developed tectonic fractures and high water abundance.The Nangong geothermal field presents a dual geothermal reservoir system,comprising shallow porous sandstone reservoirs in the Neogene Minghuazhen(lower portion) and Guantao formations,and deep fissured-karstic bedrock reservoirs in the Paleozoic Cambrian-Ordovician strata.These reservoirs host significant geothermal resources in the Nangong area.The Nangong geothermal field belongs to a heat conduction-type geothermal system within a sedimentary basin.Specifically,the heat of shallow geothermal reservoirs(temperatures:30 ℃ to 63 ℃) is sourced from the vertical conduction of regionally high terrestrial heat flow,whereas the heat of deep geothermal reservoirs(temperatures:60 ℃ to 78 ℃) originates primarily from hydrothermal convection ascending through tectonic fractures along F1 and F2,and heat transfer from surrounding rocks.The geological model for geothermal reservoirs constructed in this study demonstrates that the deep fissured-karstic bedrock reservoirs in the Nangong geothermal field are characterized by high connectivity,deep circulation,considerable thickness,extensive karst fissure development,and high permeability.Therefore,deep geothermal reservoirs in the karst fissure zone along F2 are recommended for prioritized exploitation.
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LU Xing-Chen, XING Qian, XU Yong, LYU Guo-Sen, CHEN Xiang-Zhong, WANG Rui-Xing, HUANG Shen-Shuo. Exploring the occurrence characteristics of geothermal resources in the Nangong geothermal field based on the magnetotelluric method. Geophysical and Geochemical Exploration, 2025, 49(3): 559-568.
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