Geothermal field division and its geological influencing factors in Guanzhong basin

Shallow geothermal energy is a renewable and widely distributed clean energy, it has broad prospects for development and utilization. The exploitation and utilization of geothermal energy are closely related to the division of regional geothermal field; nevertheless, there are few reports about Guanzhong basin at present. Based on regional geological and hydrogeological conditions and the classification of lithology, the authors summarized the thermal properties of rocks and soil. The influence of soil thermal conductivity and the specific heat capacity based on gray relational analysis reveal the main factors controlling the thermal conductivity and specific heat. The drying severity has the greatest impact on the thermal conductivity, whereas water content, natural gravity and porosity exhibit similar influences. The dry severity has the greatest impact on the specific heat capacity, followed by the natural gravity, whereas the water content and porosity play the weakest role. Based on the long-term observation data of downhole temperatures in the Guanzhong basin, the authors presented downhole temperature logs and temperature gradient contours. Normal temperature zone lies in the depths of 15-20 m in Guanzhong basin. The geothermal gradient is high in the middle part and low in the east and west part. The areas with large geothermal gradient include Gushi depression, Xi'an depression, Pucheng bulge and faults. The geothermal gradient of Baoji bulge, Xianyang-Liquan bulge, and Lintong-Lantian bulge is relatively small. The reasons of the differences include geological structure, groundwater activity and thermal and physical parameters of rock and soil. The heat flow in the basin was calculated using thermal physical parameters and geothermal gradient values, and the reasons which produce the heat flow difference between the shallow and the deep were analyzed. Compared with the regional geothermal background, the Guanzhong basin is hotter and its geothermal resources are abundant. The purpose of this paper is to systematically analyze the characteristics of the geothermal field in the Guanzhong basin so as to provide a basis for exploration and evaluation as well as the development of geothermal energy and to serve the construction of a good environment and society.