The Wuyi‐Yunkai Orogen experienced a polyphase tectonomagmatism and is a key region for deciphering the alteration and thermal structure of the South China Block lithosphere. Herein, an electrical resistivity model of the lithosphere is presented via the three‐dimensional inversion of broadband (0.003–3600 s) magnetotelluric (MT) data collected along a 380‐km‐long profile comprising 62 MT sites across the Wuyi‐Yunkai Orogen, and the robustness of this model is critically evaluated through a series of sensitivity tests. The resistivity model reveals that the upper crust of the Cathaysia Block and the Wuyi‐Yunkai Orogen is dominated by high‐resistivity sedimentary cover interposed with low‐resistivity features, mainly along fault zones. High‐resistivity bodies and strong conductors in the upper crust are interpreted as magmatic rocks and tectonic mélanges, respectively. Another feature of this resistivity model is the presence of zones featuring enhanced electrical conductivity (<30 Ωm) extending from the lower crust to the upper mantle beneath the Wuyi‐Yunkai Orogen. The conductors in the lower crust are attributed to saline fluids from either the dehydration of the subducting Paleo‐Pacific slab or the regional metamorphism‐induced dehydration of sandy argillaceous rocks. In contrast, the conductors in the upper mantle are attributed to 4%–7% partial melt, which corresponds to the analyses of mantle xenoliths in South China. These conductors in the upper crust and upper mantle supply volatiles and heat to shallow geothermal systems. This work ultimately shows that the lithospheric thinning of South China is controlled mainly by mantle upwelling caused by the retreat of the subducting Paleo‐Pacific slab.

Assessment of available geothermal resources in the deep oil field is important to the synergy exploitation of oil and geothermal resources. A revised volumetric approach is proposed in this work for evaluating deep geothermal potential in an active oil field by integrating a 3D geological model into a hydrothermal (HT)-coupled numerical model. Based on the analysis of the geological data and geothermal conditions, a 3D geological model is established with respect to the study area, which is discretized into grids or elements represented in the geological model. An HT-coupled numerical model was applied based on the static geological model to approximate the natural-state model of the geothermal reservoir, where the thermal distribution information can be extracted. Then the geothermal resource in each small grid element is calculated using a volumetric method, and the overall geothermal resource of the reservoirs can be obtained by making an integration over each element of the geological model. A further parametric study is carried out to investigate the influence of oil and gas saturations on the overall heat resources. The 3D geological model can provide detailed information on the reservoir volume, while the HT natural-state numerical model addressed the temperature distribution in the reservoir by taking into account complex geological structures and contrast heterogeneity. Therefore, integrating the 3D geological modeling and HT numerical model into the geothermal resource assessment improved its accuracy and helped to identify the distribution map of the available geothermal resources, which indicate optimal locations for further development and utilization of the geothermal resources. The Caofeidian new town Jidong oil field serves as an example to depict the calculation workflow. The simulation results demonstrate in the Caofeidian new town geothermal reservoir that the total amount of geothermal resources, using the proposed calculation method, is found to be 1.23e+18 J, and the total geothermal fluid volume is 8.97e+8 m³. Moreover, this approach clearly identifies the regions with the highest potential for geothermal resources. We believe this approach provides an alternative method for geothermal potential assessment in oil fields, which can be also applied globally.