Temperature field characteristics and thermal control factors of banded reservoirs geothermal field an example of Reshui-town geothermal field Hunan Province

The banded reservoirs geothermal field is a storage areas of high-quality geothermal resources, and the temperature field is a window on the thermal storage structure which is extremely unevenly distributed. Taking Reshui-town geothermal field with the highest temperature and the largest flow in Hunan Province as an example, this paper identifies six different structural areas of reservoirs through the analysis of the temperature field, water flow and drilling cores in the geothermal field, and discusses the spatial coupling relationship of thermal control factors. The main conclusions are as follows: ① The reservoir structure is controlled by the damage zone of strike-slip fracture and is divided into six areas on the plane; the main channel area, the side channel area and the seepage channel area have the well temperature curves shape of high-amplitude mushroom, high-amplitude waterfall and high-amplitude ladder; the water temperature and volume decreases accordingly; the hydrochemical type changes from HCO₃-Na type to HCO₃-Ga-Na type, and the water flow contours are distributed in bands. ② The temperature drops rapidly in the area of metamorphic rocks, indicating the water insulation effect of metamorphic rocks in the sideways; the vertical high temperature center migrates to eastward with the increase of burial depth; the fillings of SiO₂ and stilbite in the thermal reservoir cracks, and the deep hot water mainly come from the eastern granite area. ③ The geothermal fields are developed in areas with large terrain height differences, deep strike-slip faults, brittle and compact rocks area, and are jointly controlled by topography, fractures and lithology. The deep circulating hot water from the granite area is blocked laterally by metamorphic rocks in the shallow part, and finally discharged centrally in the inter-mountain depression where multiple faults intersect, forming the geothermal field with high temperature and large flow.