A preliminary study of the geothermal geological characteristics and exploration potential of the Sichuan Basin

The Sichuan Basin located in the intersection of the Tethys−Himalaya and Pacific domains is a multicycle sedimentary basin surrounded by orogenic belts. The geothermal resources are good, but with complex geological structures. Geothermal conditions and heat generation models are different in different tectonic zones in the basin, which seriously restrict the geothermal exploration, development and utilization of geothermal resources. In this paper, the distribution of geothermal resources, characteristics of geothermal fluids, heat flow and geothermal gradients in the Sichuan Basin are comprehensively analyzed by collecting the existing geothermal and petroleum exploration and development data. The geothermal reservoirs and caprocks, the burial depth and the resource conditions of different types of the basin-mountain structure areas in the Sichuan Basin are analyzed. The suggested exploration target for exploration and development are proposed in different tectonic units of the Sichuan Basin. The results show (1) the terrestrial heat flow values in the Sichuan Basin and its surrounding areas are from medium to low, and the geothermal gradient varies between 16 °C/km and 30 °C/km. The terrestrial heat source is obviously controlled by active faults and basement structure, and the hydrothermal systems are conductive and belong to the low-moderate temperature geothermal resources in the Sichuan Basin. (2) The distribution of geothermal resources in the Sichuan Basin is mainly controlled by basin structure, stratigraphic distribution and hydrologic conditions. (4) There are at least 4 karst-type geothermal reservoirs in the marine strata, and 1 − 2 glutenite-type geothermal reservoirs in clastic strata. Geothermal water is of SO₄—Ca type and is brackish. The Middle-Lower Triassic and Middle Permian carbonate rocks are considered as the best marine reservoirs, especially in the eastern and western basin. Secondly, other marine karst-type geothermal reservoirs are selected for exploration. The continental clastic rocks should be cautious because their caprocks, groundwater recharge and heat source are worse than the geothermal conditions of the marine carbonate rocks. This study may provide important guidance for further promoting geothermal exploration, exploitation and utilization in the Sichuan Basin.