Research on exploration methods for concealed geothermal resources in the hilly and mountainous areas of Fujian province

【Objective】Concealed geothermal resources in hilly and mountainous areas are buried deep underground, posing significant challenges for exploration and high investment risks. To date, there remains a lack of well-established experience in exploration work, making research into exploration methods critically important.【Methods】Taking a successful case study of concealed geothermal resource exploration in Zhangzhou as the research subject, this paper summarizes the methods and procedures for exploring concealed geothermal resources in hilly and mountainous areas. Based on regional geological, tectonic, and hydrogeological data, along with an analysis of regional hot spring distribution patterns, exploration target zones were delineated. The technical methods and sequence employed included geothermal geological surveys, simplified geophysical surveys, shallow borehole temperature measurements, geophysical exploration, and comprehensive research.【Results】Drilling verification confirmed a well depth of 1188m, successfully accessing concealed geothermal resources at intermediate-to-deep levels. The thermal reservoir lies at a burial depth of 967-1033m, with bottomhole temperatures ranging from 45.7-45.9°C. with a wellhead temperature of 37.7°C and a water yield of 628.82 m³/d (water level drawdown S = 58.65 m). This constitutes a low-temperature hot water resource. The system is of tectonically controlled conduction type, with a north-northeast trending structure as the primary heat-controlling feature. Secondary fractures derived from northwest, north-south, and north-northeast trending main structures serve as water-controlling features. The geothermal fluid exhibits an SO₄-Na·Ca chemical type with a pH of 8.49, mineralization of 244.57 mg/L, metasilicic acid content of 31.2 mg/L, fluoride content of 3.39 mg/L, and radon concentration of 63 Bq/L.【Conclusion】Research findings indicate that intermediate-to-deep hydrothermal geothermal resources can be identified in hilly and mountainous areas under suitable structural settings and hydrogeological conditions. This also validates the effectiveness of the technical methods and workflow adopted in this study within complex geological mountainous regions, providing a reference for exploring concealed geothermal resources in similar mountainous areas.