After reviewing the development of global geothermal industry as well as that in China, this paper systematically combs the key issues including the potential and the occurrence of geothermal resources in the Yangtze River Delta region, which has been mapped and announced by the central government for integrated economic development, the innovative technologies for geothermal comprehensive utilization, and the innovative models for geothermal industry development. On this basis, the paper puts forward strategic suggestions for the development of geothermal industry in the region. The main understanding is that in the economically developed Yangtze River Delta region, the population density is high, the proportion of building energy consumption is also high, and in recent years, the air temperature in the south has repeatedly set new low, and the demand for heating and cooling of residents is increasing, while relying on coal heating causes the deterioration of air quality in winter, and the shortage of clean energy is increasing, which is a difficult demand to meet in the energy sector. It can be concluded that, the Yangtze River Delta region is rich in geothermal resources, and has a large market demand and a good foundation for development and utilization, but the degree of development and utilization is still insufficient. If the top-level master plan is formulated, which is then incorporated into local social and economic planning, and guided by supportive policies, the comprehensive development and utilization of geothermal energy is expected to make greater contributions to the energy transition and meeting the goal of carbon neutrality.

In the Yangtze River Delta, there are widely distributed shallow and medium-depth geothermal energy. Based on the geothermal geology data, we estimated the geothermal energy as 78.2 billion standard coal, and the annual recoverable amount is 0.16 billion standard coal, including both shallow and medium-depth geothermal energy. It has the potential to support space heating of 2.48 billion m²，and district cooling of 1.45 billion m². However, there is currently only 57 million m² area using geothermal heating and cooling, which is less than 4% of annual recoverable amount. Further, we showed that if the current district in the Yangtze River Delta could maximize the use of geothermal heating and cooling, the CO₂ could be reduced 10% more than the current basis, and if the new buildings could all maximize the use of geothermal heating and cooling, the CO₂ could be reduced 20% more than the current basis. Therefore, geothermal energy could play an important role in the target of carbon peaking and carbon neutrality in the Yangtze River Delta.

As a clean and renewable energy, the utilization of geothermal resources has practical significance for adjustment of national energy structure, energy conservation, emission reduction, and the realization of the "dual carbon goals". The Yangtze River Delta is a favorable area for the development and utilization of geothermal resources due to its developed economy, large population density and large reserves of geothermal resources. Based on extensive research and data collection, this paper predicts the demand for building applications of geothermal resources in the Yangtze River Delta, and evaluates and analyzes the potential environmental benefits of geothermal resources development and utilization based on the demand. The results show that the building energy of geothermal resources is abundant, and the environmental benefits are significant in the Yangtze River Delta. It is believed that the comprehensive development and utilization of geothermal resources in the Yangtze River Delta region is very beneficial to promote the "integration" and "high-quality" development of the Yangtze River Delta region.

This paper introduces the working principle of some new technologies of shallow geothermal and mid-deep geothermal utilization innovative technologies such as aquifer thermal energy storage (ATES), river water source heat pump, ice source heat pump, shallow infiltration seawater source heat pump, comprehensive energy of ground source heat pump and geothermal gradient utilization. By investigating the application cases of these technologies in the Yangtze River Delta region, this paper focuses on the analysis of their advanced technologies, excellent economy and the main problems to be solved. According to their respective characteristics, the prospects for the promotion and application of these innovative geothermal utilization technologies in regions rich in geothermal resources in China, including the Yangtze River Delta, are forecasted. For aquifer energy storage, well completion technology should be optimized to avoid damage to the underground environment. The difficulties in the promotion of river water source heat pump lie in operation management. Ice source heat pump puts forward higher requirements for the preparation and transportation system of ice slurry. The implementation of shallow infiltration seawater source heat pump project must have suitable hydrogeological conditions. The ground-source heat pump integrated energy technology emphasizes the diversification and complementarity of the energy supply system, while the geothermal integrated cascade utilization technology highlights the energy gradient of the energy consumption system. The key to the promotion of these two technologies is economy.

Driven by the integrated high-quality development of the Yangtze River Delta region and the national strategy of Peak Carbon Dioxide Emissions and Carbon Neutral, generally shortened to Dual Carbon, there is a strong demand for clean energy. The Yangtze River Delta is rich in mid-deep geothermal resources. It is of great significance to study the exploring technology and method of geothermal resources in mid-deep layers in the Yangtze River Delta. Moreover, its innovation and application which will support the low-carbon development of the Yangtze River Delta will promote the exploitation and utilization of geothermal resources in mid-deep layers in this region. Based on the exploration practice of geothermal resources in the Yangtze River Delta region, this paper analyzes and studies the applicable conditions and application effects of the main technical methods of geothermal exploration in different geological structure conditions, geothermal systems and heat storage types, and forms a method system of geothermal resources exploration in the middle and deep depths of the Yangtze River Delta region. The selection of medium and deep geothermal exploration technology and method should be carried out on the basis of fully analyzing the geological background of the exploration area. It is necessary to select appropriate technology and effective combination of methods according to different geothermal geological conditions and different exploration stages to ensure good exploration effect. Gravity and magnetic exploration are suitable for detecting the information of basement, fault structure and magmatic rock distribution in sedimentary basins. We utilize controlled source audio-frequency magnetotellurics (CSAMT) and wide-field electromagnetic method(WFEM) for detecting the location of hidden thermal reservoir and thermal control structure with high accuracy, which is the most effective method to determine the location of geothermal well. The ability of microtremor survey method(MSM) to distinguish geothermal reservoir and cap rock is better than other geophysical exploration methods. Temperature measurements in shallow drillholes and radon gas survey are the most effective means to explore convective geothermal resources in shallow cover area. Different combinations of techniques and methods should be adopted in exploring geothermal resources in different geological structural units. It is advisable to use the combination of CSAMT, WFEM, MSM, gravity and magnetic method to explore deep-buried conduction-type geothermal resources in tectonic uplift area. The combination of CSAMT, temperature measurement and radon measurement should be adopted to explore convective geothermal resources. A combination of CSAMT, large pole distance electric sounding and MSM is used to explore conduction-type pore geothermal resources in sedimentary basins. The combination of CSAMT, MSM, high precision gravity and shallow hole temperature measurement is used to explore the composite geothermal resources in the uplift and depression fault zone. In the area with strong hydrothermal activity, the underground heat storage structure and geothermal anomaly range are determined by analyzing the enrichment law of some special elements in soil and groundwater. The cationic chemical temperature scale and SiO₂ temperature scale in geothermal fluid are used to estimate geothermal reservoir temperature. In general, hydrogen and oxygen stable isotopes are used to study the genesis of geothermal system. Different drilling, well formation and well washing methods should be adopted according to different geothermal reservoir types. Pore type geothermal wells with soft lithology of thermal reservoir generally adopt positive circulation mud drilling, spray well washing, polyphosphate well washing and other methods, the casing is inserted into the whole hole, and the water intake interval is formed by winding filter water pipe. For fissure geothermal wells with high lithologic hardness of hot reservoir, positive circulation mud drilling is generally adopted, which is suitable for injection well washing, polyphosphate well washing, liquid carbon dioxide well washing, compressed air well washing and other washing methods. Open hole well formation or filter pipe well formation is adopted for water intake interval. For the karst geothermal well whose reservoir lithology is carbonate rock, reverse circulation drilling and positive circulation drilling techniques can be used, and the water intake section can be formed by open hole or filter pipe. Acidizing fracturing is the most effective way to increase the water yield of karst - fissure geothermal well.

Geothermal resources are abundant in the Yangtze River Delta, but the degree of exploitation and utilization is relatively low. The geothermal resources development and utilization status, planning and management policy status of three provinces and one city in the Yangtze river delta is summarized in this paper; and the existing problems are analyzed from the aspects of government management, operation and maintenance management of geothermal projects; and then the corresponding countermeasures and suggestions are put forward.

As a kind of building heating and cooling technology, surface water source heat pump (commonly known as "water-cooled air-conditioning") technology has been applied gradually. It provides a new way to solve the problem of refrigeration (heat) in the hot summer and cold winter areas south of the policy heating line in China. The heat energy project using the Yangtze River water is developing in scale. But theoretical research on resource potential, utilization conditions and environmental effects has not kept up. In order to study the geothermal resources contained in the Yangtze River water source, the Datong Station of Yangtze river was selected as the representative section. The means of non-uniformity coefficient of runoff, Mann-Kendall method and the moving T-test method were used to analyze the hydrological regime of the Datong Station. The average annual runoff of Datong station was calculated as 905.36 billion cubic meters, and the concentration of water flow occurs in early July. According to the data of air temperature and water temperature from 2004 to 2021, it is concluded that the monthly average temperature is the highest in July and the lowest in January. The annual average water temperature is 18.9℃, and the annual average of the days when the water temperature is lower than 5℃ is 1.5 days. Therefore, it is suitable to use volumetric surface water units for heating/cooling. The water quality of Datong section is above Class II, so it meets the standard. To sum up, the water quantity, temperature and quality are suitable for the development and utilization of geothermal energy from river sources. On this basis, according to the temperature difference between air temperature and water temperature, the total geothermal resources of Datong Station are calculated as 3.08×10¹⁸ J from November to February and 1.67×10¹⁸ J from June to September. According to the control threshold of water temperature variation in the next section, the recoverable resources were calculated as 1.28×10¹⁸ J from November to February and 6.71×10¹⁷ J from June to September. The total amount of recoverable geothermal resources is equivalent to the emission reduction of about 166.04 million tons of CO₂.

In Zhejiang Province, the development and utilization of deep hot-water type geothermal resources is mainly based on hot springs and has strong social needs. However, due to the late start of the project, there is a lack of systematic study in exploration and thus the exploration success rate is relatively low. In addition, due to the low market awareness, there are also “second-time filling”phenomena in the development of hot springs. This paper begins with the type division of geothermal resources in Zhejiang Province and the quality classification of natural hot springs, considering the structural units of geothermal resources, thermal storage properties and resources-controlling structure types, and divides the geothermal resources of Zhejiang Province into three categories and nine subcategories. In addition, combining five indicators such as temperature, resource scale, quality of geothermal fluid, degree of reserve confirmation and deepening, the natural hot spring resources are classified and graded, and the hot spring resources of the province are divided into five grades. Finally, a classification and rating system that meets the actual situation of Zhejiang Province is constructed, and typical cases are analyzed, which provides scientific reference for the exploration and development and utilization of geothermal resources.

Shallow geothermal energy is an important part of clean energy, and its development and utilization meet the needs of national and social development. The technology of ground source heat pump with borehole heat exchanger (BHE) is the main technology for developing shallow geothermal energy. BHE is the core part of ground source heat pump system (GSHP), and its heat transfer performance is affected by many factors. Because the distance between the two branches of the BHE is very small, there is a serious thermal short circuit phenomenon. In the construction process of BHE, the actual distance between two branches is unknown. And different spacing will lead to different degrees of thermal short circuit, which will affect the performance of BHE. Based on the thermal response test (TRT) of GSHP project, through the combination of field test and numerical simulation, a 3D numerical model is established to study the effect of thermal short circuit between two branches of BHE on its heat transfer performance. The results show that increasing the distance between the two branches can significantly improve the heat transfer performance of the BHE. The maximum distance of two branch pipes is 22.7% higher than that of the minimum distance. The linear relationship between heat exchange and branch distance in linear meter is presented. It is suggested that pipe clamps should be strictly used in the construction of buried pipes to ensure sufficient distance between the two branches.