Present-day deep geothermal field and lithospheric thermal structure in the Ordos Basin

The Ordos Basin, a pivotal large-scale superimposed basin in China, boasts substantial oil and gas reserves. This article employs steady-state temperature (SST) from 42 wells and oil testing temperature (OTT) data from over 400 wells to conduct a comprehensive analysis of the present-day geothermal gradient, thermal properties, heat flow, and deep temperature (4 000 m, 6 000 m, and the top surface of the Proterozoic and Ordovician) in the Ordos Basin. Furthermore, the thermal lithospheric thickness (TLT), Moho temperature, and heat flow ratio of crustal to mantle are calculated. The findings reveal that the geothermal gradient within the basin mainly distributed between 22-31 °C/km, averaging at 28 °C/km. The surface heat flow, ranging from 46 to 71 mW/m², with a mean of 62 mW/m², positions the basin as a medium-temperature. Temperatures at 4 000 m and 6 000 m depths vary from 105-155 °C and 150-230 °C respectively, exhibiting a "high in the east and south and low in the west and north" pattern. Temperature at the top surface of the Ordovician ranges from 60 to 130 °C and exceeds 145 °C in the Proterozoic. The present-day TLT in the basin varies between 80 and 160 km, gradually increasing towards the west. Intriguingly, heat flow ratio of crustal to mantle in the west is significantly greater than 1, indicating a lithospheric structure of "hot crust and cold mantle". The present-day geothermal field in the basin is primarily influenced by deep thermal structures and rock thermal properties. This study contributes to the deep oil and gas exploration and basin dynamics in the Ordos Basin.