Electrical resistivity structure of the Meizhuang geothermal field in South Poyang Depression, China, revealed by 3-D magnetotelluric inversion

The Meizhuang area, located in the South Poyang Depression, is characterized by the widespread occurrence of fold-fault systems and carbonate strata. With an average surface heat flow of 72 mW/m², this region presents promising potential for developing geothermal energy. Our study aims to delineate the stratigraphic features and the components of the hydrothermal system through the interpretation of 117 broadband magnetotelluric (MT) soundings within this area. Prior dimensionality analysis using phase tensor revealed that the MT data reflects substantial lateral heterogeneities in the resistivity structure, necessitating a three-dimensional resistivity inversion. We employed the ModEM program to invert the off-diagonal components of MT impedance tensor data and comprehensively interpreted the electrical structure combined with geological information. The resistivity model major includes one low-resistivity anomaly and two high-resistivity anomalies. The conductive anomaly was attributed to the Cretaceous sandy mudstone overlaid on Permian limestone, suggesting a favorable reservoir-cap system in this location. The two high-resistivity bodies are distributed on either side of the conductive anomaly, corresponding to the Junshanhu uplift and the Meizhuang anticline respectively. These structures are mainly oriented in a northeast direction, forming a pattern of “two uplifts sandwiching one sag”. Results from this study indicate that the Permian carbonate rocks are regarded as the geothermal reservoir, while the overlying Quaternary and Cretaceous sediments serve as suitable caprocks. The presence of the Meizhuang anticline and the Junshanhu uplift facilitates deep hydrothermal circulation of groundwater along the faults.