1. 引言
1. Introduction

在全球能源革命和能源产业优化升级的背景下，地热能作为不受天气变化影响的可再生能源，因其储量丰富、安全高效和运维成本低等优点，正成为能源消费转型的重点【1】。2022年6月，国家发展改革委公布的《“十四五”可再生能源发展规划》中强调了积极推进地热能的大规模开发，并持续优化地热能开发利用的政策框架，为地热能产业的稳定增长和高质量进步提供了坚实的政策支撑。自2015年起，我国地热能直接利用规模稳居世界第一，取得了良好的经济、社会与环境效益。据研究表明，我国地热资源呈“东高、中低、西南高、西北低”的总体分布格局。受板块边缘高温地热带影响，其中藏南、滇西、川西及台湾等地是我国高温地热资源开发利用的主要靶区；而中低温地热资源分布较为广泛，主要集中于东部华北盆地、苏北盆地、松辽盆地及西部鄂尔多斯盆地等沉积盆地处【23】。迄今为止，我国已确认的地热资源储量占全球地热资源总量的8%，约等同于4000亿吨标准煤。【4】。其中，受隆起山地及沉积盆地等地质构造特征影响，安徽省内地热资源丰富【5】，预计到2025年地热能建筑供暖制冷应用面积将达到2000万平方米。因此，我国地热能开发应用潜力巨大，有望成为我国能源结构中的重要组成部分，为实现碳中和目标做出积极贡献。
In the context of the global energy revolution and the optimization and upgrading of the energy industry, geothermal energy, as a renewable energy that is not affected by weather changes, is becoming the focus of energy consumption transformation due to its abundant reserves, safety and efficiency, and low operation and maintenance costs [1]. In June 2022, the National Development and Reform Commission (NDRC) announced the 14th Five-Year Plan for Renewable Energy Development, which emphasizes actively promoting the large-scale development of geothermal energy and continuously optimizing the policy framework for the development and utilization of geothermal energy. It provides a solid policy support for the stable growth and high-quality progress of the geothermal energy industry. Since 2015, China's direct utilization of geothermal energy has ranked first in the world, and has achieved good economic, social and environmental benefits. According to the research, the geothermal resources in China show an overall distribution pattern of "high in the east, middle and low, high in the southwest and low in the northwest". Affected by the high-temperature geotropical area at the plate margin, southern Tibet, western Yunnan, western Sichuan and Taiwan are the main target areas for the development and utilization of high-temperature geothermal resources in China. However, the medium and low temperature geothermal resources are widely distributed, mainly concentrated in the sedimentary basins such as the North China Basin, the North Jiangsu Basin, the Songliao Basin, and the Ordos Basin in the west [23]. So far, China's confirmed geothermal resource reserves account for 8% of the world's total geothermal resources, which is equivalent to about 400 billion tons of standard coal. 【4】。 Among them, due to the influence of geological structural characteristics such as uplifted mountains and sedimentary basins, Anhui Province is rich in thermal resources [5], and it is estimated that by 2025, the application area of geothermal energy building heating and cooling will reach 20 million square meters. Therefore, China's geothermal energy development and application potential is huge, and it is expected to become an important part of China's energy structure and make positive contributions to the realization of carbon neutrality goals.

据统计预测，在接下来的10到15年内，我国预计有一半的铁矿资源、三分之一的有色金属矿资源以及超过半数的煤炭资源将在千米深的地下进行开采。随着开采深度的增加，矿井高温热害问题日益严峻，其与高地应力、高岩溶水压一同构成了深部开采的典型环境特征。近期，部分学者针对矿山地热资源开发利用提出了若干新颖观点。张发旺【6】等通过文献综述法总结了中国煤矿地热资源分布特征，认为利用矿山地热资源可为碳减排目标作出积极贡献。Linqi Huang等【7】针对深部开采提出了一个结合CRITIC方法和不确定性测量理论的新型热害评估框架（CRITICUM），为确保现场安全和促进地热能的可持续利用提供了有价值的参考。张吉雄【8】等提出通过相变蓄热功能充填材料置换煤炭资源，构造煤系热储开发系统，实现矿山地热能的高效开发。Austin Anderson【9】等系统讨论了地热技术的发展趋势以及利用废弃矿井进行地下能源存储和地热应用的潜力，指出矿山地热技术在未来具有重要地位。
According to statistics, it is predicted that in the next 10 to 15 years, half of China's iron ore resources, one-third of non-ferrous metal ore resources and more than half of coal resources will be mined underground at a depth of kilometers. With the increase of mining depth, the problem of high temperature and heat damage in mines is becoming more and more severe, which together with high geostress and high karst water pressure constitute the typical environmental characteristics of deep mining. Recently, some scholars have put forward some novel views on the development and utilization of geothermal resources in mines. Zhang Fawang et al. [6] summarized the distribution characteristics of geothermal resources in China's coal mines through a literature review method, and concluded that the use of geothermal resources in mines can make a positive contribution to the goal of carbon emission reduction. Linqi Huang et al. [7] proposed a novel thermal hazard assessment framework (CRITICUM) that combines the CRITIC method and the uncertainty measurement theory for deep mining ), which provides a valuable reference for ensuring site safety and promoting the sustainable use of geothermal energy. Zhang Jixiong et al. [8] proposed to replace coal resources with phase change heat storage function filling materials, and construct a coal measure heat storage development system to realize the efficient development of mine geothermal energy. Austin Anderson et al. [9] discussed the development trend of geothermal technology and the potential of using abandoned mine shafts for underground energy storage and geothermal applications, pointing out that mine geothermal technology has an important place in the future.

此外，在水热型矿山地热系统聚热模式研究方面，王贵玲【10】等提出了“同源共生－壳幔生热－构造聚热”的中国地热资源的成因理论，并基于系统论观点，详细分析了典型水热系统的运移条件、热源机制及成因模式，为区域地热资源勘查开发提供了理论依据。Yanhe Li等【11】揭示了平顶山煤田地热系统的二元构造聚热模式，指出该地区岩石热导率和区域构造的空间配置共同决定了其高地温状态。李金玺【12】等基于四川盆地及其周缘地质构造，提出了褶皱型、单斜型和褶皱-断裂复合型三种水热型地热资源的构造成因模式，认为构造运动是形成现今地温分布的主要原因。H.Barcelona【13】提出了Bañitos-Gollete地热系统的概念模型，认为研究区内N-S走向的断层系统对流体循环路径有显著控制作用，并为该地区地热研究指明方向。由此可见，矿山地热资源的开发利用已成为地热领域的重要课题，其不仅是解决深部开采热害问题的重要途径，也是实现矿山可持续发展的战略选择。
In addition, in the study of the heat accumulation mode of geothermal systems in hydrothermal mines, Wang Guiling et al. [10] proposed the genesis theory of "homologous symbiosis-crust-mantle heat generation-tectonic heat accumulation" of geothermal resources in China, and analyzed in detail the migration conditions, heat source mechanism and genesis mode of typical hydrothermal systems based on the perspective of system theory, which provides a theoretical basis for the exploration and development of regional geothermal resources. Yanhe Li et al. [11] revealed the binary tectonic heat accumulation model of the geothermal system in the Pingdingshan coalfield, and pointed out that the thermal conductivity of the rocks and the spatial configuration of the regional structure in this area jointly determine the highlandTemperature status. Based on the geological structure of the Sichuan Basin and its surrounding areas, Li Jinxi et al. [12] proposed three tectonic models of hydrothermal geothermal resources: fold type, monoclinic type and fold-fault composite type. It is believed that tectonic movements are the main reason for the formation of the current geothermal distribution. H.Barcelona [1, 3] proposed a conceptual model of the Bañitos-Gollette geothermal system, arguing that in the study areaThe N-S trending fault system has a significant control effect on the fluid circulation path and points out the direction for geothermal research in this area. It can be seen that the development and utilization of geothermal resources in mines has become an important topic in the field of geothermal energy, which is not only an important way to solve the problem of heat damage in deep mining, but also a strategic choice to achieve sustainable development of mines.

本次研究采用试验与理论分析相结合的手段，基于淮北煤田信湖煤矿地热地质背景条件，分析该区域地热水的化学组成特征及其指示意义，揭示热储温度和水循环深度。同时，查明矿区地温梯度分布规律，确定区域构造对深部矿山岩溶地热系统的控制作用，并提出信湖煤矿地热系统富水聚热模式。旨在推动地热能与煤炭生产的协同发展，优化矿山地热资源的综合利用，改善矿井作业环境，同时为碳减排及我国能源结构转型贡献力量。
Based on the geothermal geological background conditions of Xinhu Coal Mine in Huaibei Coalfield, this study analyzed the chemical composition characteristics and indicative significance of geothermal water in the Huaibei Coalfield, and revealed the heat storage temperature and water circulation depth. At the same time, the distribution law of geothermal gradient in the mining area was determined, the control effect of regional structure on the karst geothermal system of deep mines was determined, and the water-rich heat accumulation model of the geothermal system of Xinhu coal mine was proposed. It aims to promote the coordinated development of geothermal energy and coal production, optimize the comprehensive utilization of geothermal resources in mines, improve the operating environment of mines, and contribute to carbon emission reduction and the transformation of China's energy structure.

2. 区域地质概况
2. Regional geology

2.1 构造特征
2.1 Structural features

信湖煤矿坐落于淮北煤田涡阳矿区中部，该煤田是华北板块东南缘，豫淮坳陷东部的中心地带。东以郯庐断裂为界与扬子板块相接，西以夏邑-阜阳断裂为界与河淮沉降带为邻。煤田构造的形成、发展与板内构造和板缘构造的演化密切相关。区内构造受东西向构造、北东向构造、徐宿弧形构造所控制，东西向和北东向构造为主要格局。主要表现为北东向构造改造早期的东西向构造。由于多期构造运动叠加的结果，区内东西向大断裂和北北东向大断裂纵横交错，形成了许多近网状的断块构造（图1）。
Xinhu Coal Mine is located in the middle of the Wuyang Mining Area of the Huaibei Coalfield, which is the southeastern margin of the North China Plate and the center of the eastern part of the Henan-Huai Depression. It is bounded by the Tanlu fault in the east and the Yangtze plate, and is adjacent to the Hehuai subsidence zone by the Xiayi-Fuyang fault in the west. The formation and development of coalfield structure are closely related to the evolution of intraplate structure and plate edge structure. The structure in the area is controlled by the east-west trending structure, the north-east trending structure and the Xusu arc structure, and the east-west and north-east trending structures are the main patterns. It is mainly manifested in the north-east-trending tectonic transformation of the early east-west tectonic structure. As a result of the superposition of multi-stage tectonic movements, the east-west and north-north-east faults criss-cross the area, forming many near-network fault block structures (Fig. 1).

图1 淮北煤田地质构造纲要图
Fig.1 Outline map of the geological structure of the Huaibei coalfield

信湖煤矿矿井为全隐蔽区，据钻探揭露，其地层层序与淮北煤田各勘查区相同，同属华北型地层范畴。在地层层序中，淮北煤田除晚奥陶世—下石炭世和三叠纪地层缺失外，其余均发育比较齐全，各地岩性和厚度虽存在一些差异，但均可对比。具体地层岩性如图2所示，其中石炭系、二叠系为含煤地层，从上至下主要由上石盒子组、下石盒子组和山西组组成。石炭系含薄煤4～5层，宿北断裂以北局部有可采煤层，宿北断裂以南无可采煤层，二叠系含煤15～30余层，可采5～10层，主要岩性为泥岩、砂岩和煤。
According to drilling, the stratigraphic sequence of Xinhu Coal Mine is the same as that of the exploration areas of Huaibei Coalfield, and it belongs to the North China type stratigraphy. In the stratigraphic sequence, except for the absence of Late Ordovician-Lower Carboniferous and Triassic strata, the Huaibei coalfield is relatively well developed, and although there are some differences in lithology and thickness, they can be compared. The specific stratigraphic lithology is shown in Figure 2, in which the Carboniferous and Permian are coal-bearing strata, which are mainly composed of the Upper Shihezi Formation, the Lower Shihezi Formation and the Shanxi Formation from top to bottom. The Carboniferous contains 4~5 layers of thin coal, there are local mineable coal seams in the north of the Subei fault, there are no minable coal seams in the south of the Subei fault, and there are more than 15~30 layers of Permian coal, which can be mined 5~10layers, the main lithologies are mudstone, sandstone and coal.

图2 淮北煤田地层综合柱状图
Fig.2 Comprehensive histogram of Huaibei coalfield stratigraph

2.2 水文地质条件
2.2 Hydrogeological conditions

信湖煤矿作为淮北煤田水文地质单元的重要组成部分，其水文地质特征受到区域构造格局的显著影响。如图1所示，淮北煤田东有固镇～长丰断层，南有板桥断层与淮南煤田相望，西有夏邑～阜阳断层及丰涡断层与太康隆起和周口坳陷为邻。周围大的断裂构造控制了该区地下水的补给、径流、排泄条件，使其基本上形成为一个封闭～半封闭的网格状水文地质单元。根据区域地层岩性的含水条件、含水赋存空间分布，可划分为新生界松散层孔隙含水层（组）、二叠系主采煤层砂岩裂隙含水层（段）和太原组及奥陶系石灰岩岩溶裂隙含水层（段）。淮北煤田各生产矿正常涌水量为100～700m³/h，矿坑直接充水水源为煤层顶底板砂岩裂隙含水层，具有补给量不足，以静储量为主的特征。出水点水量大小与构造裂隙发育程度和补给水源有密切关系，只要没有富水含水层补给，一般水量呈衰减趋势。
As an important part of the hydrogeological unit of Huaibei coalfield, the hydrogeological characteristics of Xinhu Coal Mine are significantly affected by the regional tectonic pattern. As shown in Figure 1, the Huaibei coalfield is bordered by the Guzhen~Changfeng fault in the east, the Banqiao fault in the south and the Huainan coalfield, and the Xiayi~Fuyang fault and the Fengwu fault in the west, which are adjacent to the Taikang uplift and Zhoukou depression. The surrounding large fault structure controls the recharge, runoff and discharge conditions of groundwater in the area, making it basically form a closed ~ semi-closed grid-like hydrogeological unit. According to the water aquifer conditions and spatial distribution of water occurrence of regional stratigraphic lithology, it can be divided into Cenozoic loose layer pore aquifer (group), Permian main coal mining seam sandstone fissure aquifer (section) and Taiyuan Formation and Ordovician limestone karst fissure aquifer (section). The normal water inflow of each production mine in Huaibei coalfield is 100~700m³/h, and the direct water source of the pit is the sandstone fissure aquifer of the top and bottom plate of the coal seam, which has the characteristics of insufficient recharge and static reserves. The amount of water at the outlet point is closely related to the development degree of tectonic fractures and the recharge source, and as long as there is no recharge from the water-rich aquifer, the general water volume shows a decreasing trend.

3. Sample and method

本研究共采集信湖煤矿12份地热水样品，分别来自G1、G2、G3井基岩混合层，G4、G7、G8、G11、G12井奥陶系灰岩层，G5、G6、G10井煤层顶底板砂岩层，以及G9井F1断层处，进行水质全分析检验。样品采集后被保存于预先经过酸洗和去离子水冲洗的瓶子内，以避免外部污染。并在每个采样点均收集了充足的样本量，以便进行后续pH、TDS、主要和微量元素的测定。在现场，首先利用经过校准的便携式仪器（HQ40D）完成pH值的测定。主要阳离子和微量元素的分析样本通过使用纯硝酸酸化处理，使其pH值低于2。其中阳离子如Na⁺、K⁺、Ca²⁺和Mg²⁺等的浓度测定是通过ICP-OES（ThermoFisher IRIS Intrepid II XSP）进行的，仪器准确度在1%以内。微量元素的分析则通过ICP-MS（Agilent 7800）完成。对于阴离子的定量分析，我们采用了离子色谱法（ICS-1000）来测定F⁻、Cl⁻、NO₃⁻和SO₄²⁻等的含量，精度在5%以内。此外，SiO₂的含量测定是通过分光光度法实现的。
A total of 12 geothermal water samples were collected from the bedrock mixed layers of well G1, G2 and G3 in this study. Ordovician limestone formations in well G4, G7, G8, G11 and G12, the sandstone layers of the coal seam roof and floor in well G5, G6 and G10, and F1 in well G9At the fault, the water quality is fully analyzed and tested. After collection, samples are stored in bottles that have been pre-pickled and rinsed with deionized water to avoid external contamination. Sufficient sample volumes were collected at each sampling point for subsequent determination of pH, TDS, major and trace elements. In the field, the pH is first determined using a calibrated portable instrument (HQ40D). Samples for the analysis of major cations and trace elements were acidified with pure nitric acid to bring their pH below 2. Among them, cations such as Na⁺, K⁺, ^Ca2+and ^Mg2+, etc., concentration determination is performed by ICP-OES (ThermoFisher IRIS Intrepid II XSP).The accuracy of the instrument is within 1%. Trace element analysis is performed by ICP-MS (Agilent 7800).For the quantitative analysis of anions, we used ion chromatography (ICS-1000) to determine F⁻, Cl⁻, NO₃⁻ and SO^{4 2−}and so on, and the precision is within 5%. In addition, the determination of SiO2 content is achieved by spectrophotometry.

4. 地热水地球化学特征
4. Geochemical characterization of geothermal water

4.1 水化学分析结果
41 Results of water chemistry analysis

通过piper三线图（图3）用以描述地下水中的阴阳离子含量，可以直观地看出各水样点中的占优离子，从而对水化学相进行分类。本次研究中，我们收集来自信湖煤矿12个矿井的水文地球化学数据（表1），进行水化学特征分析。结果表明，在阳离子中，Na⁺+K⁺占阳离子总量的70%以上，Mg²⁺占比不足10%，Ca²⁺占比不足20%，说明信湖煤矿地热水中阳离子以Na⁺+K⁺为主。在阴离子中，水样点多位于右下方，主要有Cl^-、SO₄^2-、HCO₃^-等，其中以Cl^-为甚，占阴离子总量的50%~80%，表明该区域地热水主要以Na-K-Cl-SO₄型为主。此外，在水文地质学中，常利用Gibbs图（图4）分析地下水化学成分的来源和控制因素。Gibbs模型将地下水化学组分的控制因素分为降雨控制型、岩石风化型和蒸发浓缩作用型三类。图示绝大部分水样点具有高TDS，高Cl^-/Cl^-+HCO₃^-值的特征，处于蒸发沉淀区。这表明水体中的化学成分主要是由于水分蒸发导致的盐分浓缩控制的。
The Piper three-line diagram (Fig. 3) is used to describe the anions and cations in groundwater, and the dominant ions in each water sample can be visually seen, so as to classify the water chemical phases. In this study, we collected hydrogeochemical data from 12 shafts in Xinhu Coal Mine (Table 1) for hydrochemical characterization. The results showed that Na⁺+K⁺ accounted for more than 70% of the total cations, and Mg2+ accounted for more than 70% of the total cations The proportion was less than 10%, and the proportion of ^Ca2+ was less than 20%, indicating that the cation in the geothermal water of Xinhu Coal Mine was Na⁺+K⁺-based. In the anions, the water samples are mostly located in the lower right, mainly Cl^-, _SO42^-, and HCO₃^-, of which Cl^- is the most important, accounting for the total anion50%~80%, indicating that the geothermal water in this area is mainly Na-K-Cl-SO₄ type. In addition, in hydrogeology, Gibbs diagrams (Figure 4) are often used to analyze the sources and controlling factors of groundwater chemical composition. The Gibbs model divides the controlling factors of groundwater chemical composition into three types: rainfall control type, rock weathering type and evaporation concentration type. The figure shows that most of the water samples have high TDS and high Cl^-/Cl^-+HCO3^- Characteristics of the value, which is in the zone of evaporation precipitation. This indicates that the chemical composition in the water body is mainly controlled by salt concentration due to water evaporation.

图3 地热水Piper三线图
Figure 3: Three-line diagram of geothermal water Piper

表1 地热水样品水文地球化学组成
Table 1: Hydrogeochemical composition of geothermal water samples

图4 TDS与的Gibbs图
Fig.4 TDS vsGibbs diagram

Cl^-作为一种惰性示踪剂，在水岩相互作用中几乎不发生变化。因此，通过研究Cl^-与其他溶质间的相互关系，可以有效地揭示地下水中溶质的变化过程，是理解水化学演化的关键途径之一【14】。地下水中的HCO₃⁻/Cl⁻的质量浓度比是评估水循环特性的一个重要指标，当HCO₃⁻/Cl⁻的比值较高时，通常意味着地下水通过较短的流动路径迅速循环。相反，较低的比值则指示地下水经历了较慢的循环过程和较长的流动路径【15】。如图5（a）所示，信湖煤矿大部分水样分布于HCO₃⁻/Cl⁻质量浓度比低且Cl⁻质量浓度高区域，表明其热储环境较为封闭，地热流体径流时间较长，应为经历深循环所形成的岩溶地热水。在图5（b）中，Na⁺+K⁺与Cl^-之间的高度正相关性则揭示了研究区内广泛存在盐岩溶解现象。同时推测地下水发生了硅酸盐溶解或阳离子交替吸附作用，使得部分水样位于y=x线下部。
^Cl-acts as an inert tracer with little change in water-rock interactions. Therefore, studying the interrelationship between Cl^- and other solutes can effectively reveal the change process of solutes in groundwater, which is one of the key ways to understand the evolution of water chemistry [1]. 4】。 The mass concentration ratio of HCO3⁻/Cl⁻ in groundwater is an important indicator to evaluate the characteristics of the water cycleWhen the ratio of HCO₃⁻/Cl⁻ is high, it usually means that groundwater circulates rapidly through a short flow path. Conversely, lower ratios indicate that groundwater has undergone a slower cycle and a longer flow path [1, 5]. As shown in Fig. 5(a), most of the water samples from Xinhu Coal Mine are distributed in HCO₃⁻/Cl⁻The area with low mass concentration ratio and high Cl⁻ mass concentration indicates that the heat storage environment is relatively closed, and the runoff time of geothermal fluid is long, which should be karst geothermal water formed by deep circulation. In Figure 5(b), Na⁺+K⁺ vs. Cl^The high positive correlation between -indicates that there is a wide range of salt dissolution in the study area. At the same time, it is speculated that the groundwater underwent silicate dissolution or cation adsorption alternately, so that some water samples were located below the y=x line.

分析水样中的离子比例是确定水岩作用类型的重要途径。图5（c）展示了Ca²⁺与HCO₃^-之间的关系，其中G2和G3水样点位于y=2x和y=4x线之间，该分布模式表明了方解石和白云石的溶解是其水岩作用的主要过程。同时，图5（c）中G1、G4、G7、G8和G12水样点位于y=2x线的下部，其Ca²⁺浓度相对较高。结合图5（d）中相应点位于y=x线上方，共同指示这些水样中还存在着石膏（CaSO₄·2H₂O）的溶解，同时Ca²⁺参与了阳离子交替吸附作用，导致SO₄^2-的富集。此外，图5（c）中的G5、G6、G10和G11水样点分布于y=4x线的上部。结合图5（e）中对应点的Ca²⁺+Mg²⁺相较于HCO₃^-+SO₄^2-明显表现不足，该现象揭示其中可能存在硅酸盐矿物风化产生的额外阳离子中和了水中的阴离子，进而影响了水样点的离子平衡。
Analyzing the proportion of ions in water samples is an important way to determine the type of water-rock interaction. Figure 5(c) illustrates ^Ca2+ vs. HCO3^-where the G2 and G3 water samples are located between the y=2x and y=4x lines, the distribution pattern indicatesThe dissolution of calcite and dolomite is the main process of its hydrolithography. Meanwhile, G1, G4, G7, G8 in Figure 5(c). and G12 water samples were located in the lower part of the y=2x line, and their ^Ca2+ concentrations were relatively high. Combined with the fact that the corresponding point in Figure 5(d) is above the y=x-line, it indicates that these water samples are still presentGypsum (_CaSO4·_2H2O), while ^Ca2+ is involved in cation alternating adsorption, resulting in _SO42-enrichment. In addition, the water samples for G5, G6, G10, and G11 in Figure 5(c). It is distributed in the upper part of the y=4x line. Combine ^Ca2+ at the corresponding point in Figure 5(e).+^Mg2+ compared to HCO3^-+SO₄^2- Manifest deficiencies, the phenomenon reveals that there may be silicate minerals produced by weatheringThe additional cations neutralize the anions in the water, which in turn affects the ionic balance of the water samples.

图5（f）为地热水TDS质量浓度与取样标高的关系散点图，其中水样TDS与标高整体呈现负相关，此外部分浅部地热水也呈现高TDS现象。表明地热水沿倾向向深部流动并与围岩发生一系列水−岩作用致使TDS质量浓度逐渐增加，而在深部由于水压和热动力驱动使得地热水由深部向上运移，TDS质量浓度继续增加，进而导致处于浅部的水样呈现较高的TDS质量浓度。
Fig. 5(f) is a scatter plot of the relationship between the TDS concentration of geothermal water and the sampling elevation, in which the TDS of the water sample is negatively correlated with the elevation as a whole. In addition, some shallow geothermal water also exhibits high TDS. The results show that the concentration of TDS increases gradually due to a series of water-rock interactions with the surrounding rocks, while the concentration of TDS continues to increase due to the upward migration of geothermal water from the deep part due to water pressure and thermodynamic drive in the deep part, which leads to a higher water sample in the shallow partTDS mass concentration.

4.2 地球化学温标法估算热储层温度
4.2 Geochemical temperature scale method to estimate the temperature of thermal reservoirs

SiO₂地热温标作为地热勘探开发中的一个重要工具，广泛应用于地热井温度的计算。其主要基于水中溶解的SiO₂的浓度与温度之间的关系，推算出水体的温度。在许多情况下，SiO₂温标与实际温度具有较好的相关性，能够提供有效的温度估计。以下为其温度的计算公式：
As an important tool in geothermal exploration and development, SiO₂ geothermal temperature scale is widely used in the calculation of geothermal well temperature. It is mainly based on the relationship between the concentration of dissolved SiO₂ in water and the temperature, and the temperature of the water body is calculated. In many cases, the SiO₂ temperature scale has a good correlation with the actual temperature, providing a valid temperature estimate. The following is the formula for calculating the temperature:

式中，S为SiO₂的溶解度，T为热储温度。将表中灰岩段的水质全测试结果进行SiO₂温标计算，最终计算得到热储平均温度T＝48.2℃。同样的方法计算得砂岩层温度为42.9℃，其高地温特征表明存在着高温深循环地下水上升的过程。
where S is the solubility of SiO₂ and T is the heat storage temperature. The SiO₂ temperature scale was calculated from the water quality test results of the limestone section in the table, and the average temperature of heat storage T=48.2°C was finally calculated. The temperature of the sandstone layer is calculated by the same method as 42.9°C, and its high geothermal characteristics indicate that there is a process of groundwater rising in high temperature and deep circulation.

地热井中热水温度取决于地热流体循环深度，呈正相关趋势。其计算公式可表示为：
The temperature of hot water in geothermal wells depends on the depth of geothermal fluid circulation, which shows a positive correlation trend. It can be calculated as follows:

式中，Z为地下水循环深度，m；t为热储温度，℃；t₀为恒温带温度，℃；K为地温梯度，℃/m；Z₀为恒温带深度，m。结合相关资料，信湖煤矿恒温带温度约17.1℃，深度约30m【16】。由钻孔测温曲线（图6）知，煤矿平均地温梯度值为27.7℃/km。经计算得，该区地热水循环的平均深度为1153m。
where Z is the depth of groundwater circulation, m; t is the heat storage temperature, °C; t₀ is the temperature of the constant temperature zone, °C; K is the geothermal gradient, °C/m; Z₀ is the depth of the constant temperature zone, m. Combined with relevant data, the temperature of the constant temperature zone of Xinhu Coal Mine is about 17.1 °C, and the depth is about 30 m [16]. According to the borehole temperature curve (Fig. 6), the average geothermal gradient value of the coal mine is 27.7°C/km. The average depth of geothermal water circulation in this area is calculated to be 1153m.

图5 研究区水样主要离子比例图
Fig. 5: Proportion of major ions in water samples in the study area

5. 地温场分布特征及成因机制
5. Geothermal field distribution characteristics and causal mechanism

5.1 钻孔测温
51 borehole temperature measurement

钻孔测温技术在地热学领域中占据着核心地位，是直接获取区域地温分布最精确的手段。本研究选取信湖煤矿6条钻井测温曲线，测温深度0～1265m，六口钻井地温梯度值经校正后在2.4～3.2℃/hm范围内，平均地温梯度2.77℃/hm，研究区处于较低地温梯度区域。如图6所示，G2、G3、G4、G9及G11的钻孔测温曲线在整个井段内随深度的增加，温度呈线性增加，地温增温幅度基本不变，属于典型的传导型测温曲线。然而，在G1测温曲线中，随着深度的增加，地温梯度值明显减小。G1测温曲线在500～580m内表现出恒温分布特征，在500m埋深以浅时地温梯度为3.59℃/hm，处于高地温梯度水平，而在580～1026层段内地温梯度仅为2.35℃/hm。据张剑研究信湖煤矿循环上升的地下水是造成地温异常的主要因素。且信湖煤矿煤炭储层位于二叠系中下层与石炭系中，该区域具有石灰岩裂隙岩溶含水层，为地热水的循环创造了条件。由此可以推断，G1井深部岩层间存在良好的水力联系，导致地下水的活动加快了地温向地表的传导。
Borehole temperature measurement technology occupies a central position in the field of geothermal science and is the most accurate means to directly obtain the regional geothermal distribution. In this study, six drilling temperature curves were selected from Xinhu Coal Mine, with a temperature depth of 0~1265m, and the geothermal gradient values of six drilling wells were correctedIn 2In the range of 4~3.2°C/hm, the average ground temperature gradient is 2At 77°C/hm, the study area was in a lower geothermal gradient area. As shown in Figure 6, G2, G3, G4, G9 and G11The temperature measurement curve of the borehole increases linearly with the increase of depth in the whole well section, and the temperature increase amplitude of ground temperature is basically unchanged, which is a typical conductive temperature measurement curve. However, in the G1 temperature measurement curve, the geothermal gradient value decreases significantly with the increase of depth. The temperature measurement curve of G1 showed the characteristics of constant temperature distribution within 500~580m, and the ground temperature gradient was 3.59°C when the buried depth was shallow at 500m/hm, which is at the high ground temperature gradient level, while the internal temperature gradient in the 580~1026 layer is only 2.35°C/hm. According to Zhang Jian's research, the circulating rise of groundwater in Xinhu Coal Mine is the main factor causing the abnormal ground temperature. The coal reservoir of Xinhu Coal Mine is located in the middle and lower Permian and Carboniferous, and the area has limestone fissure karst aquifer, which is geothermalThe water cycle creates the conditions. It can be inferred that there is a good hydraulic connection between the deep rock layers of Well G1, which leads to the acceleration of the transmission of ground temperature to the surface due to groundwater activities.

图6 信湖煤矿典型钻孔测温曲线
Fig.6 Typical borehole temperature measurement curve of Xinhu Coal Mine

5.2 温度场
5.2 Temperature field

据研究表明，在沉积岩和火成岩中，由放射性元素（U、Th、K）衰变引起的热流密度值相对较小。此外，对信湖煤矿区域内的多个钻孔温度数据进行分析，并未发现由岩浆侵入导致的地温异常现象。因此，可以推断该地区的地热主要来源于地球深部，通过岩石介质的热传导和热对流作用，将热量传递至沉积岩层。受矿物组成及孔隙结构影响，不同岩石间的导热性能有所差异。在导热性较差的地层中，因其传热慢通常具有较高的地温梯度。
According to studies, in sedimentary rocks and igneous rocks, radioactive elements (U, Th, K) are usedThe value of heat flux due to decay is relatively small. In addition, the analysis of the temperature data of multiple boreholes in the Xinhu coal mine area shows that no geothermal anomalies caused by magma intrusion are found. Therefore, it can be inferred that the geothermal energy in this area is mainly from the deep part of the earth, which transfers heat to sedimentary rock layers through heat conduction and heat convection in rock media. Due to the influence of mineral composition and pore structure, the thermal conductivity of different rocks is different. In formations with poor thermal conductivity, they usually have a high geothermal gradient due to their slow heat transfer.

结合钻孔测温结果及前人研究，以此获得信湖煤矿北区地温梯度分布图（图7）。整体上，信湖煤矿地温梯度值为2.2~3.3℃/hm，全区平均地温梯度值为2.72℃/hm，处于正常地温梯度范围内。信湖煤矿北区内绝大部分为正断层，张性和张扭性的断裂形成了良好的导水及导热通道。其中F1断层位于井田中东部，是纵贯全区的正断层，且向东西两侧地温逐渐减小。位于F1断层西侧和F9断层北侧的区域，地温梯度相对较高，大部分在3℃/hm以上。F9断层贯穿东西，延展长度5km，其以北区域正断层密集，地温梯度明显增高；南部区域断层较少，与北部相比地温梯度值较低。这一构造热状态分布特征表明信湖煤矿北区分布着厚层的奥陶系灰岩，优先吸收变质岩深处的热量形成高温热储区。另一方面，地下水通过F9断层以北张性断裂运移沟通灰岩热储，导致煤系和灰岩热储中存在较强的水力联系，呈现高地温梯度分布特征。
Combined with the results of borehole temperature measurement and previous research, the geothermal gradient distribution map of the northern area of Xinhu Coal Mine was obtained (Fig. 7). On the whole, the geothermal gradient value of Xinhu Coal Mine is 2.2~3.3°C/hm, and the average geothermal gradient value of the whole area is 2.72°C/hm, which is in the normal geothermal gradientrange. Most of the northern area of Xinhu Coal Mine is a normal fault, and the tensile and torsional faults form good water and heat conduction channels. Among them, the F1 fault is located in the central and eastern part of the well field, which is a normal fault running through the whole area, and the ground temperature gradually decreases to the east and west. The area located on the west side of the F1 fault and the north side of the F9 fault has a relatively high geothermal gradient, most of which are above 3°C/hm. The F9 fault runs through the east and west, with an extension length of 5km, and the normal fault in the north of the fault is dense, and the geothermal gradient is significantly increased. There are fewer faults in the southern region, and the geothermal gradient value is lower than that in the northern region. This tectonic thermal state distribution indicates that there are thick layers of Ordovician limestone distributed in the northern area of Xinhu Coal Mine, which preferentially absorbs heat from the depths of metamorphic rocksFormation of high-temperature heat storage areas. On the other hand, groundwater is transported through the tensile fault north of the F9 fault to communicate with the limestone heat reservoir, resulting in a strong hydraulic connection between the coal measure and the limestone heat reservoir, showing a high geothermal gradientDistribution characteristics.

图7 信湖煤矿北区地温梯度分布
Fig.7 Geothermal gradient distribution in the northern area of Xinhu Coal Mine

5.3 地热系统成因机制
5.3 Genesis of geothermal systems

综合上述分析，在查明研究区的构造特征、断层、地层以及水文地质条件的基础上，并结合北区高地温梯度的分布特征，本研究提出了信湖煤矿地热系统的成因机制模型（图8）。该模型揭示了北区高地温梯度的分布特征是由深部热量的传导作用与地热水的对流作用共同影响的结果。
Based on the above analysis, on the basis of identifying the tectonic characteristics, faults, strata and hydrogeological conditions of the study area, and combining with the distribution characteristics of the geothermal gradient in the northern area, a genetic mechanism model of the geothermal system of Xinhu Coal Mine was proposed in this study (Fig. 8). The model reveals that the distribution characteristics of the geothermal gradient in the northern region are the result of the combined influence of deep heat conduction and geothermal water convection.

（1）信湖煤矿北区广泛发育张性及张扭性的导水正断层，为不同层位间提供了有效的水力连接。此外，煤系地层之下赋存着厚层奥陶系灰岩，这些地质特征共同构成了北区高地温梯度现象的地质基础。（2）相较于煤层及砂岩，灰岩具有更高的热导率，是一种高效的热传导介质。其能够优先吸收来自深部变质岩层的传导热量，随着温度的逐渐升高，形成了位于煤层之下的优质富水热储层，温度约为48.2℃。（3）研究区的热储环境相对封闭，地热水经历了漫长的径流过程，表现为经历深层循环的岩溶地热水。地热水的循环深度约为1153米，并在径流过程中与周围围岩进行了充分的热交换，从而形成了高温地热水。（4）在深层循环对流过程中，被加热的地下水在热动力和地压的共同作用下，沿着导水断层（例如F9、F1断层）上升，将深层的热量输送回煤系地层，导致断层周边区域出现地温梯度显著增加的现象。
(1) Tensile and torsional transducible normal faults are widely developed in the northern area of Xinhu Coal Mine, which provides an effective hydraulic connection between different horizons. In addition, the thick Ordovician limestone is hosted under the coal measure strata, and these geological features together form the geological basis of the high-geothermal gradient phenomenon in the northern region. (2) Compared with coal seam and sandstone, limestone has higher thermal conductivity and is an efficient heat conduction medium. It can preferentially absorb the conduction heat from the deep metamorphic rock formation, and with the gradual increase of temperature, a high-quality water-rich heat reservoir is formed under the coal seam, with a temperature of about 48.2°C. (3) The heat storage environment in the study area is relatively closed, and the geothermal water has undergone a long runoff process, which is manifested as karst geothermal water undergoing deep circulation. The geothermal water circulates to a depth of about 1,153 meters and is fully heat exchanged with the surrounding rock during the runoff, resulting in high-temperature geothermal water. (4) In the process of deep circulating convection, the heated groundwater rises along the water diversion faults (such as F9 and F1 faults) under the combined action of thermodynamics and ground pressure, and transports the heat from the deep layers back to the coal measure strata, resulting in a significant increase in the geothermal gradient in the surrounding area of the fault.

图8 信湖煤矿北区地热系统成因机制
Fig.8 The genesis mechanism of the geothermal system in the northern area of Xinhu Coal Mine

6. 结论
6. Conclusion

（1）淮北煤田信湖煤矿地热水化学组成特征表明，地热水中阳离子以Na⁺和K⁺为主，阴离子主要为Cl^-、SO₄^2-、HCO₃^-，地热水类型主要为Na-K-Cl-SO₄型。水化学分析和Gibbs模型揭示了水体化学成分主要受蒸发浓缩控制，且存在盐岩溶解现象。
(1) The chemical composition characteristics of geothermal water in Xinhu Coal Mine in Huaibei Coalfield show that the cations in the geothermal water are mainly Na⁺ and K⁺, and the anions are mainly Cl^-, _SO42^-, HCO3^-, geothermal water types are mainlyNa-K-Cl-SO type ₄. The water chemistry analysis and Gibbs model revealed that the chemical composition of the water was mainly controlled by evaporation and concentration, and there was salt rock dissolution.

（2）通过SiO₂地热温标法估算，信湖煤矿热储平均温度为48.2℃，砂岩层温度为42.9℃，显示出深部高温地下水上升的地热特征。奥陶系灰岩水平均循环深度为1153米，是经历深循环的岩溶地热水。
(2) According to the SiO₂ geothermal temperature scaling method, the average temperature of Xinhu coal mine heat storage is 48.2°C, and the temperature of sandstone layer is 42.9°C, which shows the geothermal characteristics of the rise of deep high-temperature groundwater. The Ordovician limestone has an average circulation depth of 1153 meters and is karst geothermal water that undergoes a deep cycle.

（3）信湖煤矿地温梯度分布特征显示，全区平均地温梯度值为2.72℃/hm，处于正常地温梯度范围内。特别是在F1以西及F9以北的区域，地温梯度较高，表明该区域存在较强的水力和热力联系。
(3) The geothermal gradient distribution characteristics of Xinhu Coal Mine show that the average geothermal gradient value of the whole area is 2.72°C/hm, which is within the normal geothermal gradient range. In particular, the geothermal gradient is higher in the area west of F1 and north of F9, indicating that there is a strong hydraulic and thermal connection in this region.

（4）信湖煤矿地热系统的成因机制模型表明，北区高地温梯度分布特征是由深部热量的传导作用与地热水的对流作用共同影响的结果。地温梯度的分布受到构造特征、断层和地层的综合影响，煤系下伏的奥陶系灰岩和伸展断裂奠定了热储富水及导热的地质基础。
(4) The genesis mechanism model of the geothermal system of Xinhu Coal Mine shows that the distribution characteristics of high geothermal gradient in the northern area are the result of the combined influence of deep heat conduction and geothermal water convection. The distribution of geothermal gradient is affected by the comprehensive influence of tectonic characteristics, faults and strata, and the Ordovician limestone and extensional faults under the coal measure have laid the geological foundation for heat storage, water enrichment and heat conduction.

1我国中深层地热资源赋存特征、发展现状及展望
1. Occurrence characteristics, development status and prospect of medium and deep geothermal resources in China

2中国中-高温地热资源勘探方向与优选靶区
2. Exploration direction and preferred target area of medium-high temperature geothermal resources in China

3中国地热资源概况及开发利用建议
3. Overview of geothermal resources in China and suggestions for development and utilization

4中国地热资源及其潜力评估
4. Evaluation of geothermal resources and their potential in China

5安徽长江经济带地热资源赋存特征及潜力评价
5Evaluation of geothermal resource occurrence characteristics and potential in the Yangtze River Economic Belt in Anhui Province

6废弃煤矿山地热资源开发利用研究
6. Research on the development and utilization of geothermal resources in abandoned coal mines

7 Huang, L., Wei, Y., Chen, Z., Wang, Z., Liu, Y., Sun, L., & Li, C. (2024). Thermal Hazard Evaluation and Prediction in Deep Excavations for Sustainable Underground Mining. Sustainability, 16(24), 10863.

8深部矿山相变蓄热功能充填采热构想及技术体系
8. Phase change heat storage function filling and heat mining concept and technical system of deep mines

9 Anderson, A., & Rezaie, B. (2019). Geothermal technology: Trends and potential role in a sustainable future. Applied Energy, 248, 18-34.

10我国主要水热型地热系统形成机制与成因模式
10 Formation mechanism and genesis mode of major hydrothermal geothermal systems in China

11 Li, Y., Yu, K., Wan, Z., Zhang, Y., Wang, Z., Shi, P., ... & Zhang, B. (2024). Regional structural controls on a hydrothermal geothermal system in the eastern dingshan coalfield, China: A comprehensive review. Geothermics, 123, 103131.

12四川盆地水热型地热资源构造成因模式
12 Structural genesis model of hydrothermal geothermal resources in Sichuan Basin

13 Barcelona, H., Lelli, M., Norelli, F., Peri, G., & Winocur, D. (2019). Hydrochemical and geological model of the Bañitos-Gollete geothermal system in Valle del Cura, main Andes Cordillera of San Juan, Argentina. Journal of South American Earth Sciences, 96, 102378.

14苏北盆地典型地区中低温地热流体地球化学特征研究
14 Study on the geochemical characteristics of low-temperature geothermal fluids in typical areas of the North Jiangsu Basin

15华北型煤田奥陶系岩溶水水文地球化学特征及其对地热的指示意义
15 Hydrogeochemical characteristics of Ordovician karst water in North China coalfield and its indicative significance to geothermal energy

16信湖煤矿地温分布特征及影响因素分析
16 Analysis of geothermal temperature distribution characteristics and influencing factors in Xinhu Coal Mine