Geothermal Geological Characteristics and Genetic Model of the Shunping Area along Eastern Taihang Mountain

Abstract

Knowledge about subsurface geological characteristics and a geothermic genetic model plays an essential role in geothermal exploration and resource assessment. To solve the problem in the Shunping area along eastern Taihang Mountain, geothermal geological conditions were analyzed by geophysical, geochemical, and geological methods, such as magnetotelluric, gas geochemistry, and structural analysis. The geothermic genetic model was developed by analyzing the characteristics of the heat source, water source, migration channel, reservoir, and cap rock of the geothermal geological conditions. Favorable deep thermal conduction conditions and sufficient atmospheric precipitation in the study area provide an original heat source and water supply for geothermal formation. The faults and unconformities of different scales have become effective channels for the migration of underground hot water. The thermal reservoir formed by marine carbonate rocks with karst fissure development provides suitable space for the storage of underground hot water. Although the Cenozoic strata have good thermal insulation and water insulation function, the thermal insulation and water insulation effect is not ideal because of the shallow coverage in the Shunping area and the damage by tectonic action, which affected thermal insulation and water insulation to some extent, restricting the practical preservation of underground heat energy in the Shunping area. The bedrock geothermal resource in the Shunping area is original from the combined action of multiple indexes of source, transport, reservoir, and cap. The geothermal geologic conditions of source and reservoir in the Shunping area are very similar to those in the Xiongan new area, and have obvious advantages in hydrodynamic conditions. Although limited by the cap’s effectiveness, the geothermal resources in the Shunping area can provide some clean energy support for local production and life, thereby satisfying economic development conditions and encouraging further geological exploration.

1. Introduction

Geothermal resources provide clean and renewable energy. With the increasing environmental problems and shortage of energy, it has become a universal consensus to intensify the development of geothermal and other renewable energy sources [1,2]. China has about 16.7% of global geothermal resources, especially the medium- and low-temperature geothermal resources, which means that geothermal energy has great utilization potential [3]. It is of great significance to strengthen the study of geological characteristics of different geothermal systems for scientific guidance of regional geothermal resources exploration and exploitation.

The knowledge of subsurface geological characteristics and a thermal genetic model plays an essential role in geothermal exploration and resource assessment [4,5]. Exploration of geothermal resources needs comprehensive multidisciplinary (geological, hydrological, geochemical, and geophysical) surveys through the use of traditional methods and innovative techniques for the geothermal potential assessment [6,7]. From the viewpoint of system theory, Wang and Lin [8] put forward three typical characteristics of the genetic model of geothermal resources in China: hydrothermal heat and dry heat coexist with the same source, mantle heat flow and crustal heat flow are the most essential heat sources, and faults of different scales and levels play a role in heat accumulation.

The early exploration of geothermal resources in Hebei province was mainly aimed at heat storage in the Neogene Minghuazhen Formation and Guantao Formation. For example, the Niutuozhen, Rongcheng, and Xinji geothermal fields achieved good results and were put into thermal springs, heating, and breeding [9,10]. In recent years, the study of bedrock heat storage in Hebei Province has become a research hotspot. For example, good bedrock heat storage has been found in Niutuozhen, Xiongan new area (XNA), and Xianxian geothermal field [11,12,13,14]. Because of the limitations of early technology, the eastern margin of Taihang Mountain, where Shunping is located, has not been regarded as a promising area by geothermal researchers. With improved technical means and the deepening of heat storage exploration depth, geothermal exploration in the piedmont area of Hebei province has made significant breakthroughs. Wang Guiling et al. [15] divided the hydrothermal–geothermal resources in the Beijing–Tianjin–Hebei region into sedimentary basin conduction and uplifted convective types, according to the different tectonic types, causes, and heat transfer modes. The geothermal reservoirs in Jizhong Depression include pore type, fracture type, and fracture–cavern type. They are adjacent to the heat resources, and most of them have good cap rock [16]. Li Feng et al. [17] studied the geothermal–geological conditions near the Taihang piedmont-front fault in the Handan area and found that the thermal reservoirs of the Triassic Heshanggou and Liujiagou Formations were characterized by low water volume and high water temperature. Liu Juan [18] evaluated the rock types, reservoir space, and main controlling factors of the Wumishan Formation reservoir in the Jizhong Depression and divided the Wumishan Formation reservoir into three types. Song Mian et al. [19] analyzed the geochemical and scaling characteristics of geothermal water in Fuping County of Taihang Mountain and concluded that the underground hot water in the Fuping district was slightly corrosive and moderately corrosive, and there was a possibility of scaling by the geothermal water, mainly calcium carbonate scale. Based on the analysis of hydrochemical and isotopic data from 26 sets of Wumishan Formation geothermal fluid samples from Taihang Mountain and XNA, it was concluded that the geothermal fluid supply source in the Wumishan Formation heat reservoir in XNA is meteoric water [20]. The fluid penetrates into the deep strata through regional faults or fractures, and generates water–rock interaction and absorbs heat provided by the crust–mantle source in the long-distance runoff process, thus forming geothermal water. Therefore, although predecessors have carried out some work on understanding the bedrock heat storage and obtained some basic knowledge, research on the geothermic genetic mechanism of bedrock heat storage at the front of Taihang Mountain is insufficient.

In this paper, combined geophysical, geochemical, and geological methods, such as magnetotelluric, gas geochemistry, and structural analysis, are used to determine the geothermal geological characteristics of the Shunping area along East Taihang Mountain. Based on the analysis of the characteristics of the geothermal source, pathway, reservoir, and cap, a geothermic genetic model for the Shunping area is established.

2. Geological Background

The Shunping area is a part of the Bohai Bay Basin, within the North China Craton (NCC), located in East Taihang Mountain and connected to the North China Plain. The Taihang Mountain area is located in the northwest, and the North China Plain is located in the southeast. From northwest to southeast, mountains, hills, and plains are sequentially arranged (Figure 1). This study was mainly carried out in the middle and southeast of the Shunping area on the eastern edge of Taihang Mountain (Figure 2).

As a part of the NCC, the study area experienced a complete process of craton formation and evolution: Formation stage of continental nucleus; Massive growth stage of continental crust; Microcontinental fragmentation and cratonization; Great Oxidation events and Earth environmental upheaval during the Paleoproterozoic; Active zone structure and metamorphism to high-grade granulite facies during the Paleoproterozoic; Multistage rift and middle Earth adjustment period during the Meso-Neoproterozoic; Marginal orogeny during the Paleozoic; Tectonic transition and decratonization during the Mesozoic [21,22].

The development characteristics of the pre-Cenozoic in the study area are consistent with the whole NCC [23]. The Middle Proterozoic and overlying sedimentary cap rocks are widely developed on the Archean–Paleoproterozoic crystalline basement, but the Upper Ordovician and Lower Carboniferous are generally absent and the Neoproterozoic Qingbaikou System is partially absent. The Taihang Mountain area where the study area is located has relatively complete strata exposed at the surface. From old to new, the strata include Archaeozoic (Fuping Group); Paleoproterozoic (Hutuo Group); Meso-Neoproterozoic (Changcheng System, Jixian System, Qingbaikou System); Paleozoic (Cambrian, Ordovician, Carboniferous, and Permian), and Mesozoic (Jurassic), with sporadic distribution of Paleogene (Figure 1).

Taihang Mountain is an extensional orogenic belt composed of tectonic magma belts and metamorphic core complexes. The orogenic belt uplifted rapidly, and a large number of denuded clasts filled the North China Basin. At the same time, the deep crust–mantle material in the rift basin migrated to the Taihang Mountain uplift area to supplement the space for the lower mantle depression of the orogenic belt and the uplift of the mountain systems. Additionally, with the continuous development of the orogenic belt, the lithosphere was balanced to form the coupling relationship between the rift basin and the extensional mountains [24].

Through the MT profile from Taihang Mountain south of Shijiazhuang to the Jizhong Depression, predecessors have concluded that the lithospheric electrical properties have the characteristics of vertical stratification and horizontal block [25]. Moreover, the electrical structures of the Taihang Mountain uplift belt and the Jizhong Depression are completely different. The Taihang Mountain uplift belt is a high-resistance body. In the basin area, the electrical properties in the crust are roughly distributed in layers, and low-resistivity layers developed from the surface to a depth of about 7 km. These low-resistivity layers should be the Upper Paleogene Formation (E–Q) and composed of loose sediments.

The groundwater distribution in Shunping area is mainly controlled by stratum lithology, regional structure, and its secondary structure. Groundwater in this area mainly comes from atmospheric precipitation. The supply mode is carried out by vertical seepage of fracture and fissure. Quaternary unconsolidated sediments, Ordovician limestone, and Jixian–Changcheng dolomite are the main water-rich strata in the area. With the increase in water consumption due to population growth, the water table is decreasing yearly. Quaternary loose sediments alone can no longer meet the water needs of local residents. Local residents have mainly relied on the Ordovician Jixian System, in which groundwater is sufficient. Abundant groundwater resources provide a good source of water for geothermal exploration.

3. Methods

3.1. Magnetotelluric

Magnetotelluric (MT) sounding is a mature exploration geophysical technique. It is a frequency-domain electromagnetic sounding method for studying middle and deep geological structures. Its basic principle is to use the natural electromagnetic fields widely distributed on the Earth according to the differences in electromagnetic properties between different rock strata and between rocks and ores in the Earth’s crust. It is widely used in geothermal field exploration [26,27,28,29].

The Aether magnetotelluric system, produced by the CG Company of the United States, is used in this study. It has two electric and three magnetic (five channel) data acquisition functions. The acquisition unit is light, small, and easy to operate, with great flexibility. Additionally, it is more suitable for working environments such as terrain fluctuation and lakefront because there is no need for a cable connection between receivers. The magnetotelluric inversion and interpretation processes are shown in Figure 3.

Obtaining high-quality raw data is the basis for establishing a reasonable three-dimensional electrical structural model. The study area is densely populated, the power grid is dense, and various electromagnetic interferences are strong. This study adopted the method of combining robust analysis technology and remote reference technology (single point or multipoint) to process time-domain data to obtain apparent resistivity and impedance phase data. A “dead band” distortion correction was performed using Rhoplus analysis technology. Using impedance tensor decomposition technology, the underground geoelectric structure is analyzed, and local distortion analysis and correction are carried out. The curve translation method, the two-dimensional (2D) inversion method with terrain and surface heterogeneity, and the spatial filtering method are used to analyze and correct the static displacement generated by the shallow heterogeneity, strengthen noise identification and elimination, and improve data quality.

Before MT data inversion, we conducted dimensional analysis and strike analysis. Bahr skew determined that the underground electrical structure is mainly partial to 2D [30]. For a one-dimensional (1D) regional conductivity structure, a single coordinate-invariant phase is equal to a 1D impedance tensor, which is the characteristic of the phase–phase tensor. If the regional conductivity structure is 2D, the phase tensor is symmetric with one of its major axes parallel to the strike axis of the domain structure. In the case of 2D, the dominant values (coordinate invariants) of the phase tensor are the transverse electric and magnetic polarization phases [31]. The phase tensor analysis determined that the geoelectric strike direction is NE 35°. The nonlinear conjugate gradients (NLCG) code [32] was used for 2D inversion. The algorithm employs an NLCG scheme to minimize objective functions that penalize data residuals and second-order spatial derivatives of resistivity. After 109 iterations, the inversion was finished and root-mean-square (RMS) misfit is 2.1.

3.2. Gas Geochemistry

Joint Rn–Hg measurement of gas in the soil is a gas geochemical detection technology, and the research objective is to characterize the gas halo formed by Rn and Hg gaseous molecules migrating in gaseous form from deep sources and its geological indication [33]. The air-Hg from the deep crust is related to degassing of the upper mantle, and the air-Hg from the shallow crust is related to volcanic eruptions, tectonic magmatic activity, earthquakes, and geothermal activity. Under the action of large temperature and pressure gradients, deep air-Hg penetrates fractures of deep origin and some secondary or lower fractures leading to them. The air-Hg from shallow sources is mainly from active structures, the rock mass, or an ore body, and its air-Hg concentration is relatively higher. Air-Hg migrates from deep into the surface and diffuses to the atmosphere, which is the basis for tracing faults and structural fracture zones on the surface.

An XG-7Z mercury meter and FD-3017RaA transient radon meter were used. The active gas extraction method was adopted. A hole about 1.2 m deep is made at the measuring point with a steel drill, and the hole was tightened with an auger to prevent air leakage. The electrostatic filter membrane filter, mercury capture tube, dryer, and radon meter were connected through a silica gel tube. Three liters of soil gas (two cylinders) was extracted manually to measure Hg and Rn.

4. Geothermal Geological Characteristics

Based on MT, Rn–Hg survey results, and structural analysis, the geothermal–geological conditions in the Shunping area of Hebei province are analyzed from the aspects of source (heat source, water source), pathway (fluid pathway), reservoir (geothermal reservoir), and cap (cap rock).

4.1. Heat Source

The heat source is an essential condition for the formation of geothermal fields. The heat source in the study area is mainly composed of two parts: one is the disintegration heat of radioactive elements such as U, Th, and K in the shallow crust, and the other is heat conduction from the upper mantle [10,34]. Previous studies show that the buried depth of the Moho surface in the Shunping area is about 37–38 km, which is conducive to the heat conduction of the upper mantle (Figure 4).

The terrestrial heat flow in the Bohai Bay Basin is closely related to the regional structure and crustal thickness. The characteristics are as follows: (1) The heat flow in the basin is higher than that in the surrounding mountainous areas. The average heat flow of the whole Jizhong Depression is 63.1 mW/m² [10], which is close to the average heat flow of the Bohai Bay Basin, 64 ± 8 mW/m² [36,37,38], while the average heat flow of west Taihang Mountain is generally less than 50 mW/m² [39]. (2) The middle–high value of heat flow is where the crust is relatively thin in the basin. This is because the heat flow is higher in areas where the lithosphere is stretched and the crust is relatively thin due to more heat conduction from depth (Figure 5). The thinning of the thick lithosphere in North China was mainly caused by continental lithosphere extension caused by the rotation of the ancient Pacific subduction plate and the retraction of the ocean trench during the Late Mesozoic [40,41,42,43]. (3) Locally, the geothermal heat flow in the depression area is lower than that in the uplift area, mainly controlled by the tectonic pattern of inner convex and concave basins [39,44]. The average heat flow value of the Shunping area is about 50 mW/m², which is slightly lower than that of the Jizhong Depression in the east. However, according to the above rules, the heat flow value of the Shunping area is still higher than that of Taihang Mountain, especially since the eastern plain area is still a good heat source area.

4.2. Water Source

Atmospheric precipitation is the main supply source of underground water in the study area, mainly completed through vertical leakage between fractures or fissures [20,45]. In the piedmont area, the atmospheric precipitation becomes surface water, and rapidly becomes groundwater through channels such as faults or fissures, and enters vertically into thermal reservoirs. The geothermal water of sandstone and carbonate thermal reservoirs in and around the study area is derived from atmospheric precipitation in the Taihang Mountain area.

The Taihang Mountain area, to which the Shunping area belongs, is mainly a bedrock outcropped area with shallow carbonate strata distribution, and geothermal fluid is in an open oxidation environment with good hydrodynamic conditions, a short flow path for geothermal fluid, and a rapid water cycle [20].

4.3. Geothermal Reservoir

The exploitation and utilization of geothermal resources in Hebei plain and some piedmont areas are realized by exploiting underground hot water, so hot water must be stored. Owing to the influence of piedmont cold water recharge, the heat storage temperature of the Minghuazhen Formation in the Shunping area is less than 25 °C, which is lower than the 25 °C lower limit for geothermal resources. Therefore, only the heat storage of the Neogene Guantao Formation and the bedrock heat storage are considered in the study area. The bottom boundary of the Neogene Guantao Formation is 800–2000 m, and the stratum thickness is 200–800 m. The thickness of the thermal reservoir is generally less than 100 m, and the temperature of the thermal reservoir is 25–35 °C [46].

As can be seen from the MT interpretation profile (Figure 6), the Cenozoic thickness west of the F1 Taihang Mountain piedmont fault is less than 2000 m, the buried depth of the bottom boundary of the Guantao Formation is less than 1000 m, and the depth of the bottom boundary of the Guantao Formation to the east of the F1 fault is more than 3000 m, and the buried depth of the bottom boundary of the Guantao Formation is 200–1500 m from west to east. On both sides of the piedmont fault of Taihang Mountain, a huge thickness of Proterozoic and Paleozoic marine carbonate rocks were deposited, and the cumulative thickness of the stratum is about 6–7 Km. The Wumishan Formation of the Jixian System of Middle Proterozoic is the most important geothermal reservoir in the study area, with the most complete sequence and the largest thickness. The Jixian System comprises grayish brown siliceous dolomite in a restricted platform environment, intercalated with argillaceous dolomite and thin mudstone, rich in stromatolites and well-developed fractures (Figure 7).

Previous studies have shown that the piedmont fault zone of Taihang Mountain was mainly formed in the Paleogene [47]. It is basically developed in the upper crust, and most faults in the study area are shovel-shaped positive faults with a gentle dip. In particular, the Baoding–Shijiazhuang and other faults in the middle–north section of the fault zone are large and gentle detachment faults, extending horizontally for tens of kilometers on their inclinations. The Taihang Mountain piedmont fault is a large spade-shaped fault, accompanied by a right-slip, which controls the formation of the Bohai Bay Basin [23,25]. The Jizhong Depression formed a tectonic pattern dominated by faults in the west and superposition in the east, as shown in the profile of Figure 6.

4.4. Cap Rock

Good caking conditions are conducive to forming an excellent water-repellent layer, and the underground hot water is well stored in the thermal reservoir of the underground hot field. The cap rock in the study area is mainly Quaternary, and there is no cap rock in some piedmont areas with loose structure, large porosity, and poor thermal conductivity, which has a good thermal insulation effect. The cap rock covers the Neogene system, forming a good cap rock. Generally, a thick clay layer under the cap rock forms a good waterproof layer. In addition, the Neogene stratum is not only a thermal reservoir itself, but also a good cap rock for the underlying bedrock geothermal reservoir.

Using the F1 Taihang Mountain piedmont fault as the boundary, the cap rock thickness in the study area shows an obvious difference. The thickness of the Quaternary to the west of the F1 Taihang Mountain piedmont fault is about 0–200 m, and the thickness of the Quaternary to the east of F1 is about 100–450 m, which shows an obvious increasing trend from west to east. The Quaternary sediments are mainly composed of silty clay and clayey silt, with a clay layer locally embedded, forming a particular waterproof layer and becoming an effective cap layer for the lower geothermal reservoir.

To the west of the F2 fault, the Proterozoic Jixian System is exposed at the surface, and the cap rock conditions are poor, lacking an effective water-repellent layer.

4.5. Fluid Pathway

In general, the heat from the deep crust is transferred to the surface in two ways: firstly, the deep heat is transferred to the surface in the form of hydrothermal convection with water as the carrier along the deep fault zone; the other is the transfer of deep heat to the surface through various rock layers in the form of heat conduction. The anomalous geothermal areas are distributed beadlike along the fault zone and mainly at the intersection of deep and large faults. In these parts, the secondary structures are extremely well developed, the rock is broken, and the ground stress is relatively reduced, which provides good conditions for the upwelling of deep hot water. Meteoric water or surface water recharges groundwater along the deep fault zone. The groundwater in the fault zone upwells along the water channel of the fault zone after deep circulation heating and hydrothermal convection, and remains in the shallow heat reservoir to form an anomalous geothermal area.

The fractures and unconformities of different sizes in the study area are hot water migration channels (fluid channels). The precipitation from the Taihang Mountains in the west is transported to the thermal reservoirs through faults and unconformity surfaces, especially the faults (F2, F3, and their secondary faults) in the bedrock outcrop area of the Taihang Mountains, which are well connected with the surface water and the thermal reservoirs, together with the heat source. It can be noted from the anomaly diagram showing Hg in the soil (Figure 8) that the distribution of the Hg anomaly is obviously in the NE direction, indicating the two faults that pass through Yaozishan village and Cailiang village. Their positions are relatively consistent with the F2 fault location predicted by MT, and they are the main fault and branch fault of F2. The Hg anomaly in the middle area of the two faults indicates multiple secondary faults in the area, which can communicate atmospheric precipitation and thermal reservoir well. The intensity of the Rn anomaly is weaker than that of the Hg anomaly (Figure 9), but the predicted faults of the Rn anomaly zone in the north are consistent with the northern fault structure F2 inferred by Hg, and Rn anomalies also mainly distributed in the NE direction. Rn anomalies show that the NE-trending faults in the southeast are close to F1, confirming the existence of F1 and its secondary faults.

5. Discussion

5.1. Geological Modeling

Conclusions can be drawn by analyzing the source–pathway–reservoir–cap (SPRC) characteristics of geothermal geological conditions in the Shunping area. Favorable conditions of deep thermal conduction in the study area and ample atmospheric precipitation provide a basis for geothermal heat and water source (source). Different sizes of faults and unconformity surfaces became the effective underground hot water migration (pathway). The thermal reservoirs formed by marine carbonate rocks with karst and fissure development provide a suitable space for the storage of underground hot water (reservoir). Cenozoic, especially Quaternary and Neogene, have good thermal and water insulation functions. However, owing to the shallow cover-layer in the Shunping area, coupled with the geological framework created by tectonic activity, the effect of heat insulation and water isolation have a particular impact, which restricts the practical preservation of underground heat energy in the Shunping area (cap). Based on the MT interpretation profile, the formation depth is determined by referring to borehole data in the study area and surrounding areas (

Table 1. Formations encountered by drilling within the research area.

Borehole Number	Location	Altitude	Depth	Drilled Strata
				Q	N	E	O	∈	Jxw	Ar
ZK003	South of Zhaipozhuang Village, Shunping County, Hebei province	78.5	70	14.4	/	/	/	/	/	70
Zk501	About 500 m northwest of Zhaizi Village, Nantaiyu Town, Shunping County, Hebei province	218.72	125.58	/	/	/	124.88	125.58
g30	North of Beichaoyang Village, Shunping County, Hebei Province (shown in Figure 2)	65.4	12.5	11.8	/	/	/	12.5
SNC1	Southeast corner of cement plant, Shunping County, Hebei Province	52.5	180.14	29		/	180.14
CKB20	North of Wujiazhuang Village, Baoding city, Hebei Province	27.15	220.77	147.5	220.77
I-4	1500 m northwest of Fangshunqiao Village, Mancheng County, Hebei province	34	450.48	450.48

Note: “/” indicates that the stratum is not exposed. Data source [48].

), and the geothermic genetic model of the Shunping area is established. The bedrock geothermal resource in the Shunping area results from the comprehensive action of multiple indexes of source, pathway, reservoir, and cap (Figure 10).

5.2. Comparison with Adjacent Areas

XNA in Hebei province, located in the northwest of the study area, has played a good role in geothermal resource exploration and effective utilization [49,50]. Its tectonic unit is located in the Jizhong Depression of Bohai Bay Basin, on the east side of the Taihang Mountain piedmont fault. XNA and Shunping area are located on both Taihang Mountain piedmont fault sides.

The water supply of the XNA and Shunping area is mainly meteoric precipitation from the Taihang Mountain area [50,51]. The main bedrock thermal reservoirs are carbonate rocks of the Wumishan Formation of the Middle Proterozoic Jixian System. They have certain similarities in geothermal–geological conditions.

The differences in geothermal geological conditions between the Shunping area and the XNA are mainly reflected in two aspects: hydrodynamic and caking conditions.

The Shunping area, which belongs to the Taihang Mountain area, is mainly a bedrock outfall area, where carbonate rocks are shallowly distributed, and geothermal fluids are in an open oxidation environment with good hydrodynamic conditions, a short flow path, and a rapid water cycle. However, the deep carbonate geothermal fluid in XNA is relatively closed with poor hydrodynamic conditions, a long flow path of geothermal fluid, a slow water cycle, and significant water–rock interaction [20]. Therefore, compared with XNA, the Shunping area has apparent advantages in hydrodynamic conditions.

Owing to severe tectonic movement and denudation, the thickness of the Cenozoic in the Shunping area is generally less than 1000 m, and the thickness of the Quaternary is generally less than 200 m. The thickness of the Cenozoic in the XNA (Figure 11) is about 1500–2500 m, and the thickness of the Quaternary is 300–457 m [50]. Compared with XNA, the cover layer in the Shunping area is thinner, which restricts the practical preservation of underground heat energy to a certain extent. As mentioned above, the terrestrial heat flow value in the Taihang Mountain area in the Shunping area is slightly lower than that in the Jizhong Depression, which is also related to the thin cover-layer condition in the Shunping area. It is worth mentioning that it is not the thicker cover that is more conducive to preserving underground heat energy, but a suitable range is needed [50,52].

In addition, under the condition of the thin cover, practical geothermal fields can still exist as long as there is good water isolation. For example, the thickness of the geothermal cap in the Yangbajing area of Xizang Province is 100–250 m [53], and the thickness of the geothermal cap in the Changli area of Hebei Province is 150–420 m [54]. The thickness of the cover layer is not very large, but the geothermal field with utilization value is formed under the effective water isolation condition and a good source–pathway–reservoir–cap system.

6. Conclusions

Based on the comprehensive geophysical and geochemical exploration and geological analysis methods such as magnetotelluric, gas geochemistry, and tectonic analysis, the geothermal geological conditions of the Shunping area in the eastern margin of Taihang Mountain are analyzed. The research indexes can be divided into five aspects: heat source, water source, fluid pathway, reservoir, and cap rock characteristics.

A geothermic genetic model of the Shunping area is established. The geothermal storage space of karst-fissured marine carbonate rocks, effective convection, and migration channels formed by faults and unconformity, proper deep heat flow, sufficient water supply from Taihang Mountain, and good hydrodynamic conditions all provide favorable conditions for the occurrence of geothermal resources in the Shunping area. The Cenozoic, especially Quaternary and Neogene, has good thermal and water insulation conditions. However, owing to the shallow covering layer in the Shunping area and the damage by tectonic action, the effect of thermal preservation and water insulation is affected, which limits the practical preservation of underground thermal energy in the Shunping area.

The bedrock geothermal resource in the Shunping area resulted from the comprehensive action of multiple indexes of source, pathway, reservoir, and cap. The geological conditions of source and reservoir geothermal in the Shunping area are very similar to those in XNA and have obvious advantages in hydrodynamic conditions. Although the geothermal resources in the Shunping area are limited by the poor caprock effectiveness, with the improvement of technical means and the strengthening of geological exploration, it can still provide a certain amount of clean energy support for local production and life. A potential geothermic genetic model needs to be formed under a good source–pathway–reservoir–cap system.