Heat flow and associated thermal regimes are related to the tectonic evolution and geophysical properties of the lithosphere. The Ordos Basin is located in a tectonic transitional zone: areas to the east of the basin are characterized as tectonically active, while regions to the west of the basin are characterized as tectonically stable. It is of general interest to learn the geothermal characteristics of the basin in such tectonic conditions. To clarify the spatial variability of the present-day geothermal field across the basin and its implications, we report 13 terrestrial heat flow points based on the first systematic steady-state deep borehole temperature measurements in the basin. The new data together with existing data show that the geothermal gradients in the basin range from 12.6 to 42.3 °C km⁻¹ with a mean of 27.7 ± 5.3 °C km⁻¹; the terrestrial heat flow values range from 43.3 to 88.7 mW m⁻² with a mean of 64.7 ± 8.9 mW m⁻². Such values are higher than those of typical cratonic basins and lower than those of tectonically active areas. By using all these data in the basin and adjacent areas, we plot geothermal gradient and heat flow distribution maps. The maps reveal that the basin is cooling westwards and northwards. The distribution pattern of the geothermal field is consistent with the lithospheric thickness variation in the basin. This similarity suggests that the geothermal spatial variability of the Ordos Basin is mainly influenced by heat from the deep mantle. In the southeastern basin, we locate a positive geothermal anomaly caused by the convergence of heat flow in basement highs and the high radiogenic heat production. In addition, the high heat flow in the eastern basin is related to the intense uplift during the Cenozoic Era.

The Xiong’an New Area is located at the western Bohai Bay Basin, 150 km south of Beijing, China. The area has tremendous high heat flow value within the sedimentary layer, and the average value can reach 90 mW·m^-2 within the Niutuozhen Uplift. However, combining the basal heat flow at the top of the metamorphic layer with the heat flow value which was contributed by the radiogenic heat production from the overlying formation, the surface heat flow value was only 65.1 mW·m^-2 in this area. Thus, the heat flow value within the sedimentary layer was greatly influenced by other factors. In this study, based on the continuous temperature measurements data from 4 boreholes, thermos-physical parameters (conductivity, radioactive heat production, density, and heat capacity) from 90 rock sample measurements, and the regional stratigraphic development, a two-dimensional thermal-hydraulic modelling was carried out to study the influence of the heat refraction and groundwater convection on the heat flow value. According to calculation results, the heat flow disturbance caused by heat refraction was 10 mW·m^-2, and the disturbance value was 20 mW·m^-2 for the groundwater convection. Furthermore, when the high-permeability layer thickness was a certain value, with the increasing high-permeability layer buried depth, the influence of the groundwater convection on the temperature field which was used for the heat flow calculation became weak. While when the high-permeability layer buried depth was set up, the influence of the groundwater convection on the above temperature field became stronger with the increasing high-permeability layer thickness.

The Ordos Basin is rich in oil and gas resources in the Paleozoic strata. The southern part of the basin boasts a thick Paleozoic sedimentary sequence, enriched organic matter, favorable sedimentary facies, and hydrocarbon source rocks with an over-mature thermal evolution stage. However, the lack of in-depth study of the tectono-thermal evolution in the southern basin limits regional oil and gas exploration. In this study, drill core and outcrop samples were collected from the Shanbei Slope and the Weibei Uplift, respectively. These samples were subjected to apatite fission track (AFT) and (U-Th)/He dating (AHe). The results were used to reconstruct the thermal history of the southern basin, calculate exhumation rates, and analyze the tectonic evolution of the basin. The seven annealed AFT data values from the Shanbei Slope range from 21.4 to 52.8 Ma, with mean track lengths of 13.24 μm, and the twelve unannealed AFT data values from the Weibei Uplift range from 111.9 to 204.6 Ma. The seven AHe data values from the Shanbei Slope range from 17.0 to 31.8 Ma, and the eight AHe data values from the Weibei Uplift range from 31.7 to 47.5 Ma. The thermal history is characterized by a prolonged phase of burial and heating from the Triassic to the Late Early Cretaceous, followed by a phase of uplift and cooling that continued into the Cenozoic. This cooling phase exhibits three distinct stages with varying rates of uplift and cooling. According to the dating results, the cooling timing of the southern basin was earlier than that of the central part, and the southern basin experienced higher uplift rates during the Paleogene than in other periods of the Cenozoic. This may be attributed to the far-field effects of the collision between the Indian Plate and the Eurasian Plate during the Paleogene.

Doublet system has been widely used in the geothermal system heat extraction, which mainly involved the hot groundwater extraction and geothermal water reinjection into the underground thermal reservoir. Many factors can influence the thermal reservoir performance, such as the production or injection mass flow rate, injection fluid temperature, and lateral well spacing. In this study, taking the specific heat capacity varying with the formation temperature, the rock porosity, and permeability variations into consideration, a three‐dimensional thermo‐hydraulic coupled numerical model was established to assess the influence of heat capacity variation with formation temperature and other correlation parameters on the sandstone and carbonate thermal reservoir performance over a period of 40 years. Results show that the influence of specific heat capacity variation on the thermal reservoir performance was less than the rock porosity variation and less than the rock permeability variation. On the other hand, the influence of the above three parameter variations is more significant on the sandstone reservoir than the carbonate formation, in which the specific heat capacity variation hardly made any difference for the carbonate thermal reservoir, but for the sandstone reservoir, the specific heat capacity and its temperature variation can yield a 1.3 K decreasing for the average output temperature and a 0.02 × 10⁷ W decreasing for the average energy production rate over the 40 years. Finally, in this case, the temperature and energy production rate from the production well is higher after considering the rock porosity variation no matter for the sandstone or the carbonate. But the result may be opposite after changing the initial and boundary conditions or parameter selection. The influence of rock permeability variation on the thermal reservoir performance was also studied, which can produce a decreasing 10.1 K for the average output temperature and 0.19 × 10⁷ W for the energy production rate over the 40 years.

The study of tectono-thermal evolution of sedimentary basins reveals both geothermal field characteristics and hydrocarbon generation and expulsion in the basin. However, there are only a few studies on the tectono-thermal evolution of the Fuyang Sag. This means the hydrocarbon exploration in the study area is restricted and unable to be effectively supported. Based on the geophysical exploration and drilling results, the tectono-thermal evolution of the Fuyang Sag has been studied for the first time in this paper. Using the organic geochemical data of the source rocks, the influence of tectono-thermal evolution on hydrocarbon exploration in the Fuyang Sag was discussed. The burial history of the Fuyang Sag since the late Paleozoic falls into four stages: stable sedimentation, rapid subsidence and deposition, long-term continuous uplift and denudation, and sedimentation. The heat flow evolution history of the Fuyang Sag since the late Paleozoic is characterized by ascending first and descending afterward. The main source rocks in the sag increased rapidly during the Permian and was gradually finalized in the Yanshanian period. The Fuyang Sag was reformed after the early hydrocarbon generation. The main source rocks with deeper burial depth, weaker uplift, and denudation reformation have greater potential for hydrocarbon exploration in the sag. The results of this study provide not only a scientific basis and important guidance for hydrocarbon exploration in the Fuyang Sag, and but also effective geothermal constraints for further geodynamics research in the Southern North China Basin.