Analysis of the Formation Mechanism of Medium and Low-Temperature Geothermal Water in Wuhan Based on Hydrochemical Characteristics

Abstract

Wuhan and its surrounding areas have obvious geothermal spring outcrops, which are unexplored potential geothermal resources. The degree of geothermal resource development in Wuhan is low, and there is a lack of systematic research on their hydrochemical characteristics and formation mechanism. The Wuhan area is bounded by the Xiang-Guang fault, the South Qinling-Dabie orogenic belt in the north, and the Yangtze landmass in the south, with Silurian and Quaternary outcrops and little bedrock outcrops. The Silurian is the main water barrier in the region, which separates the upper Triassic and Paleogene as shallow aquifers and the lower Cambrian and Ordovician as deep aquifers. Different strata are connected by a series of fault structures, which constitute Wuhan’s unique groundwater water-bearing system. Eleven geothermal water (23~52 °C) and six surface water samples (around 22 °C) were collected from the study area. The geothermal water in the study area is weakly alkaline, with a pH of 7.04~8.24. The chemical type of geothermal water is mainly deep SO42− with a higher TDS and shallow HCO3− type water with a lower TDS. Isotopic analysis indicates that atmospheric precipitation and water-rock interaction are the main ionic sources of geothermal water. The chemical composition of geothermal water is dominated by ion-exchange interactions and the dissolution of carbonates and silicates. The characteristic coefficients, correlation analysis, water chemistry type, recharge elevation, geothermal water age, reservoir temperature, and cycle depth were also analyzed. The performance was similar in the same geothermal reservoir, which could be judged as an obviously deep and shallow geothermal fluid reservoir, and the genetic conceptual model of Wuhan geothermal was preliminarily deduced. DXR-8 and DXR-9 had the best reservoir conditions, hydrodynamic conditions, rapid alternation of water bodies, and large circulation depth, which is a favorable location for geothermal resource development and will bring considerable economic and social benefits.