Evaluation of favourable hot dry rock areas in the east of the Yishu fault zone in China

Abstract

Hot dry rock (HDR) geothermal resources have great development potential and prospects, owing to their wide distribution and high thermal storage temperature. HDR resources are abundant in China, but their exploration and exploitation remain in the early stages. The Yishu fault zone in Shandong Province in eastern China is in a high-temperature geothermal zone of the Pacific Rim. Three craters and 15 hot springs are in this area, which possesses abundant geothermal resources and favourable conditions for the occurrence of HDR resources. Nevertheless, HDR resources in this area have not been studied in detail, and the index-evaluation system for HDR is still imperfect. In this paper, five index layers are selected, including: the gravity and magnetic fields, geothermal field, tectonic activity, reservoir and cover characteristics, and remotely sensed features. Thirteen index elements were also selected as evaluation factors. In combination, these index layers and index elements have established a favourable evaluation index system for HDR resources in this region, and the analytic hierarchy process has been used to determine the weight of each factor. Then, the GIS spatial analysis function is used to carry out spatial superposition analyses for each index element, and finally the distribution characteristics of HDR resources east of the Yishu fault zone were determined, with four favourable selection areas being delineated. The occurrence conditions of HDR resources are analysed in detail with evaluation indexes. It is believed that HDR resources are closely related to neotectonic movement, volcanism and rocks with high heat-generation rates. Searching for areas with geothermal anomalies is indispensable for the evaluation of HDR resources. This study provides a basis for the exploration and development of HDR resources in the region, and it can also provide a reference for similar work in other parts of the country. KEY POINTS A set of evaluation indexes to determine favourable areas for HDR resources, including gravity, geothermal field, geological structure and crustal stability, heat storage and heat cover and features on remotely sensed images, is established. East of Yishu fault zone, there is a great potential of HDR resources, with an area of 19 399 km2 of favourable and more favourable areas, accounting for approximately 38.8% of the total area. HDR resources are likely closely associated with neotectonics, igneous activity, geothermal anomalies and rocks with a high heat-generation rate such as granites.