Characteristics of Geothermal Resource and Geothermal Reservoir In Central Guangdong Depression

Huizhou area is situated at east of Guangzhou City in southern Guangdong Province, adjacent to developed cities, such as Shenzhen and Hong Kong. Previous studies in Huizhou area proved that Huizhou area is rich in intermediate- to high-temperature geothermal resources for their exceptional geological advantages, for instance, abundant heat source from intense geotectonic and magmatic events since late Mesozoic, deep faults as geothermal channel, i.e. Lianhuashan and Heyuan faults, favorable reservoirs like limestone and fractured granite, ideal cap-rocks with proper depth to prevent thermal fluid from dissipating upwards. Nevertheless, forming mechanism and detailed distribution of geothermal resources in the area are still unclear, which retard exploration and production of geothermal energy in Huizhou area. In order to improve exploration efficiency and decrease cost expenditure for geothermal companies, the paper try to figure out problems of geothermal formation and distribution of Huizhou area through analyzing thermophysical properties and geochemical ingredient for geothermal reservoir. In the area, deep geothermal is mostly developed in Meso-Cenozoic sedimentary basins and the surrounding areas, such as Yanshanian granite and Paleozoic carbonate reservoirs, which were buried in a proper depth and distributed widely, the most potential for large-scale geothermal resource development. It can be easily concluded from thermophysical property analysis that the Yanshanian granite presents higher thermal conductivity but lower specific heat capacity than Paleozoic limestone, implying that limestone is an ideal geothermal reservoir rather than granite. Observed from outcrops and drilling cores, Paleozoic limestones are mostly featured by corrosion holes or pores because of dissolution, which are favorable reservoir for storage of geothermal fluid, while granites are difficult to be dissolved instead of fractures. Geochemically, limestone is more dissolvable than granite and sandstone that enable reservoir-form easily and scale-forming. Accordingly, reservoirs in Huizhou area are divided into three types considering their thermophysical properties, geochemical and exploration prospect, i.e., carbonate reservoir, granite reservoir and sandstone reservoir. As a potential geothermal area, upper Carboniferous and middle to upper Devonian carbonate rocks are excellent for geothermal reservoir.