Geothermal Development Model in Granite Area: a Case Study of Shangyun Area, Yunnan Province, China

Abstract

The Shangyun area is classified as a medium-high temperature geothermal region situated in western Yunnan, inside the tropical zone of Yunnan and Tibet. Granites exhibit a wide distribution, while active faults demonstrate a rather advanced state of development. Consequently, the geological conditions are favourable for the creation of geothermal resources. Drawing upon previous research findings and geothermal drilling data, this study undertakes an analysis of the principal geological factors contributing to the development of the Shangyun geothermal system in Yunnan. The investigation reveals several noteworthy characteristics of geothermal activity within the granite region, including proximity to heat sources, substantial thermal gradients, water accumulation within fractures, the coexistence of deep and shallow geothermal phenomena, and the occurrence of hot springs along extensive and profound fault lines. The determined ground heat flow value in the Shangyun area is 142.74 mW/m², with its primary heat source being predominantly influenced by high mantle heat flow and the radioactive heat generation of the Lincang granite located in the eastern region with the mean rate of radioactive heat generation of 7.6 μW/m³. The reservoir space mostly consists of weathered crust and fracture type heat storage. Additionally, the upper Jurassic mudstone, which has a thickness ranging from 500 to 1000 m and a thermal conductivity of 2.39 W/(m K), serves as an effective regional cap layer. The dissolution of silicate has a significant impact on the composition of geothermal water, with the primary type being HCO₃–Na. The process of atmospheric precipitation infiltration and recharge contributes significantly to the availability of ample water resources for geothermal systems. Based on an analysis of the electrical data pertaining to the region, it can be inferred that the primary source of the water supply originates from the eastern mountain. Furthermore, it is seen that the active fault serves as the conduit for the deep circulation of geothermal water. This study presents a comprehensive examination of several geothermal geological features, including heat source, heat storage, hot channel, and geothermal water, in order to build a geothermal model specific to the Shangyun region.