ABSTRACT The deep karstic aquifer containing hot water is ideal for space heating and maybe also for geothermal power generation. The hot water is characterized by high single-well yield, low salinity, gravity injection and less impact on environment when it is exploited. In order to run a karstic geothermal field sustainably, it is of high importance to identify the local groundwater circulation pattern in the field. Here we take Xiongxian geothermal field as an example to get insights into the characteristics of local groundwater circulation in karstic aquifers. Groundwater samples and surface water samples were collected, and analyzed for their hydrochemical and isotopic contents. Results show that the TDS of groundwater in karstic aquifers is between 1.9 and 2.6 g/L. According to the data of water table, the local groundwater flow direction is from Southwest to Northeast. This is confirmed by the TDS data, which increases gradually in this direction. However, this is orthogonal to the regional groundwater flow direction that is from Northwest to Southeast. This phenomenon highlights the control of aquifer lithology and geological structures on the groundwater flow field. Isotopic data illustrates some oxygen isotope shifts, although the reservoir temperature is less than 90 ℃. Finally, a conceptual model is proposed to depict the deep groundwater cycle in Xiongxian geothermal field, which will serve as a basis for the further simulated model for exploitation strategy and could be used as a reference in similar karstic aquifers

Ji Luo

Jumei Pang

Lu Luo

Olaf Kolditz

Shao Habing

Yanlong Kong

Zhonghe Pang

CiteSeerX

Proceedings World Geothermal Congress 2015  
Melbourne, Australia, 19-25 April 2015 
1 
Deep groundwater cycle in Xiongxian geothermal field 
Yanlong Kong
1, 2
, Zhonghe Pang
1*
, Jumei Pang
1
, Lu Luo
1
, Ji, Luo
1
, Habing, Shao
2
 and Olaf, Kolditz
2
 
1 Key Laboratory of Engineering Geomechanics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 
100029, China  
2 Helmholtz Centre for Environmental Research (UFZ), Leipzig, Germany 
*Corresponding author: z.pang@mail.iggcas.ac.cn 
 
Keywords: Groundwater cycle; Geothermal system; Karstic reservior; Isotope; Xiongxian; China 
ABSTRACT  
The deep karstic aquifer containing hot water is ideal for space heating and maybe also for geothermal power generation. The hot 
water is characterized by high single-well yield, low salinity, gravity injection and less impact on environment when it is exploited. 
In order to run a karstic geothermal field sustainably, it is of high importance to identify the local groundwater circulation pattern in 
the field. Here we take Xiongxian geothermal field as an example to get insights into the characteristics of local groundwater 
circulation in karstic aquifers. Groundwater samples and surface water samples were collected, and analyzed for their hydro-
chemical and isotopic contents. Results show that the TDS of groundwater in karstic aquifers is between 1.9 and 2.6 g/L. According 
to the data of water table, the local groundwater flow direction is from Southwest to Northeast. This is confirmed by the TDS data, 
which increases gradually in this direction. However, this is orthogonal to the regional groundwater flow direction that is from 
Northwest to Southeast. This phenomenon highlights the control of aquifer lithology and geological structures on the groundwater 
flow field. Isotopic data illustrates some oxygen isotope shifts, although the reservoir temperature is less than 90 ℃. Finally, a 
conceptual model is proposed to depict the deep groundwater cycle in Xiongxian geothermal field, which will serve as a basis for 
the further simulated model for exploitation strategy and could be used as a reference in similar karstic aquifers. 
1. INTRODUCTION  
The geothermal energy available from the Earth is potentially enormous, spanning a wide range of heat sources including 
hydrothermal resources and hot dry rock (HDR) energy. Among them, the hydrothermal systems taking advantage of heated 
groundwater is the kind in wide use. 
Sufficient production of groundwater with constant temperature is most crucial for large scale utilization of hydrothermal resources. 
In this regard, the deep karstic aquifer containing hot water is ideal for space heating and maybe for geothermal power generation. 
The features of high single-well yield, low salinity, gravity injection and less impact on environment characterize the exploitation 
of karstic aquifers. In China, more than 80% of geothermal water is obtained from karstic aquifers (Pang et al., 2012). 
Xiongxian geothermal field is located in Niutuozhen uplift, which has a total area of 640 km2, with the area within Xiongxian 
territory being around 320 km2. The recoverable heat in Xiongxian geothermal field is estimated to be 2.5 × 1018 J (Huang et al., 
2012; Liu et al, 2014). Geothermal water in Xiongxian has been used for more than 30 years, with reservoir temperature ranging 
from 50°C to 95°C. The geothermal energy is mainly used for space heating, bathing and greenhouse agriculture. Space heating 
starts from November 15th every year and ends on March 15th the next year.  
With the rapidly growing demand for energy, and increasing concern for climate change, large use of geothermal energy is highly 
expected. But overexploitation may cause resource depletion and other environmental problems (Duan et al., 2011). Taking 
Xiongxian as an example, we note that the water table has dropped by 30 m from 2001 to 2009. After 2009, many injection wells 
were installed in order to maintain the water table. For the sustainable use of geothermal water in Xiongxian, subsurface 
characterization is critical, while the research on deep groundwater cycle could serve as a basis. 
2. STUDY AREA 
Xiongxian lies in the North China Plain (NCP). It is at a distance of 108 km from Beijing and 100 km from Tianjin (Fig. 1). The 
Xiongxian geothermal system is situated in the Niutuozhen uplift, which is located north of the Jizhong Depression, and is a part of 
the Bohai Bay Basin (BBB). The BBB, one of the major petroleum and gas producing areas in eastern China, covers Bohai Bay and 
coastal areas with an area of about 200,000 km2. It is a large Mesozoic - Cenozoic intra-cratonic sedimentary basin filled by 
continental sediments of Paleocene, Neogene and Quaternary ages. It was formed in the Tertiary on the basement of the North 
China Platform, and consists of many separate Paleogene faulted depressions. During the Neogene, the whole area subsided and 
became united into a great depression (Pang et al., 2013). 
The boundary of the Niutuozhen Uplift consists of four main faults (Fig. 1 and Fig .2). They are the Niudong fault, the Niunan 
fault, the Rongcheng fault and the Daxing fault, which were created by folding movement from the Late Jurassic to the Cretaceous, 
during the Himalayan movement. The Xiongxian geothermal system is located in the southwest from the larger Niutuozhen 
geothermal system. The main geothermal reservoirs are porous Tertiary sandstone and karst-fissured dolomite bedrock. The strata 
of the Xiongxian geothermal system and surroundings include Quaternary and Tertiary formations in Cainozoic, Jixian System and 
Changcheng System in Proterozoic and Archaeozoic. 
Kong et al. 
 2 
 
Figure 1 Locations of Niutuozhen uplift and Xiongxian geothermal field in China. The red block scheme illustrates the 
Niutuozhen uplift with faults as boundaries. The orchid polygon shows the extent of Xiongxian. 
 
Figure 2 Tectonic map and a cross section of Xiongxian geothermal field in Niutuozhen uplift (Reivsed from Ma et al., 
1990). 
Kong et al. 
 3 
3 SAMPLING AND ANALYSES 
Samples of hot and cold waters were collected in Xiongxian geothermal field in 2013. Field parameters, including pH, dissolved 
oxygen (DO), Eh, electrical conductivity (EC) and temperature were recorded at the time of sample collection. Samples were later 
analyzed in the Water Isotopes and Water-Rock Interaction Laboratory, Institute of Geology and Geophysics, Chinese Academy of 
Sciences. δ2H and δ18O were measured on a laser absorption water isotope spectrometer analyzer (Picarro L2120-i). All δ2H and 
δ18O values are expressed related to Vienna Standard Mean Ocean Water (V-SMOW) in ‰, and the measurement precision was 0.5 
and 0.1‰ for δ2H and δ18O, respectively. The analysis of water chemistry was completed using ion chromatography in Analytical 
Laboratory of Beijing Research Institute of Uranium Geology. The methods for cation measurements are taken from the National 
Analysis Standard DZ/T0064.28-93 while for anions are from DZ/T0064.51-93. Alkalinity was measured on automatic titrator (785 
DMP™). Analytical precision was 3% of concentration based on reproducibility of samples and standards and detection limit was 
0.1 mg/L. 
4. RESULTS AND DISCUSSION 
4.1 Groundwater flow direction 
Water table of geothermal water in the karstic reservoirs was measured in May, 2013, two months after the four month long 
pumping period for space heating. Given the consistency of surface elevation of each well, the groundwater depth is used to map 
the groundwater flow direction. Groundwater is found to move toward northeast in the urban region of Xiongxian geothermal field 
(Fig. 3). The spatial variation of Total dissolved solids (TDS) was then used to determine the groundwater flow direction in a larger 
extent from Rocheng uplift to Xiongxian uplift, according to the recognition that TDS escalates following the movement of 
groundwater. 
 
Figure 3 Groundwater flow direction indicated by water table and TDS in the study area. 
Interestingly, the local groundwater flow direction we found in Xiongxian geothermal field is not consistent but orthogonal to the 
regional flow direction, which is from northwest towards southeast. Zhou et al. (1989) found that recharge for Niutuozhen uplift is 
from Taihang and Yanshan Mountains with two major flow paths: one is through the Langfang-Guan sag in the north, and the other 
is from Xushui sag and Rocheng uplift in the west. With their findings in mind, one can see a groundwater jet stream comes from 
the west in Figure 3. Meaningfully, it turns to northeast in the urban region of Xiongxian, which actually refers to the axis of south 
Niutuozhen uplift. As was claimed above, Niutuozhen uplift is encircled by several normal faults. Among them, Niudong and 
Niunan faults in the east and south are identified as barriers of weak groundwater conductivity (Zhou et al., 1989). Such a barrier 
forces groundwater to move northeast in the axis of the uplift and decelerate gradually to the boundary surrounded by low 
permeability sandstone. Then the hindered movement of groundwater in the horizontal domain enhances its flow in the upward 
direction, when the so-called leakage recharge occurs. The finding of groundwater flow justifies the existence of higher temperature 
groundwater in the top of Niutuozhen uplift and its cap rock consisted of Neogene reservoirs. Ma et al. (1990) pointed out that TDS 
in the Neogene reservoirs above the axis of Niutuozhen uplift is larger than TDS in other parts within the same region, which 
confirms our explanation on groundwater flow. The leakage recharge between different deep aquifers will be further demonstrated 
in the following sessions based on hydro-chemical and isotopic data. 
4.2 Water-rock interaction 
Stable isotopes of different water bodies including cold water in quaternary aquifers and thermal water in Neogene and Jixianian 
aquifers are used to illustrate water-rock interaction and hydraulic connectivity between them. Classifications can be easily found 
due to the distinct behaviors of the isotopic locations in Fig. 4. Cold water with water table less than 200 m is more enriched in 
isotopes than cold water with water table more than 200 m. The radiocarbon ages of them are less than 10000 years and more than 
14000 years, respectively (Table 1). As a counterpart research on shallow groundwater in North China Plain (NCP), Chen et al. 
(2003) claimed that groundwater recharged by precipitation in the late Pleistocene have ranges of −9.4 to −11.7‰ for δ18O and 
Kong et al. 
 4 
−76‰ to −85‰ for δ2H values, while groundwater recharged by precipitation in the Holocene have ranges of are −7.7‰ to 
−10.2‰ of δ18O and −63‰ to −73‰ for δ2H values, respectively. The differences of isotopic data suggest that groundwater 
beneath and above the depth of 200 meters are in independent systems with weak hydraulic connectivity between them. 
Table 1 TDS and radiocarbon age of groundwater in different aquifers 
 Quaternary (<200 m) Quaternary(>200 m) Neogene* Jixianian 
TDS (mg/L) 300 - 600 100 - 500 500 - 1500 1900 - 2600 
Age (ka) <10 14 - 25 25 - 30 31 - 36 
*The data of Neogene geothermal water is cited from Ma et al. (1990) 
The isotopic values of Neogene thermal water are well between those of the two groups of cold water differentiated by depth (Fig. 
4). By contrast, Jixianian thermal water illustrates a clear trend of oxygen shift. The phenomenon of oxygen shift is very common 
in high temperature geothermal system as a result of 18O exchange between groundwater and reservoir rocks (Clark and Fritz, 
1997). It may also be observed in the middle-low temperature geothermal system by exchanging 18O of groundwater with reservoir 
carbonates over long residence time and low water-rock ratios (Qin et al., 2005). Besides the oxygen isotope change, the hydrogen 
values of Jixianian thermal water seem larger than those of Quaternary groundwater with depth larger than 200 m. According to our 
analysis above, precipitation in the late Pleistocene has lower values of δ18O and δ2H due to the cooler climate. Thus Jixianian 
groundwater with an age of 31 – 36 ka (Table 1) should be more depleted in or close to groundwater isotopes in the Quaternary 
with depth larger than 200 m. The reason might be related to the releasing of CH4 in a reducing environment, where many oil and 
gas fields are adjacent. Further evidences should be presented in this regard. 
 
Figure 4 Stable isotopes of different water bodies in Xiongxian geothermal field. The solid line represents the global 
meteoric water line (GMWL). The dashed line shows the oxygen shift of thermal water in the Karstic reservoir. 
4.3 Conceptual model 
Based on the geological, hydrogeological and hydrogeochemical data, a conceptual model of deep groundwater cycle is proposed. 
During the cooler climate in the late Pleistocene, precipitation in the Taihang and Yanshan Mountains infiltrated, went through 
Langfang-Guan sag, Xushui sag and Rongchen uplift and finally turned to be the regional recharging source for Niutuozhen uplift 
from Northwest. On the local scale, after that the groundwater moved into Xiongxian geothermal filed, south Niutuozhen uplift, 
they were blocked by Niudong and Niunan faults in the east and south and then turns to move toward northeast in the horizontal 
domain and upward in the vertical domain. Leakage recharge may occur between Neogene and Jixianian aquifers. 
5. CONCLUSIONS 
Recharge mechanisms and timing for Xiongxian geothermal field have been considered on the basis of multiple isotopic and 
hydrochemical tracers. Several key aspects of the system are elucidated by the available data:  
(1) On the local cycle, groundwater flow direction is found to change from northwest to northeast in the axis of Niutuozhen uplift 
as a result of tectonic structure. The change of flow direction enhances the heat convergence in Niutuozhen uplift and even aquifers 
in its cap rocks. 
(2) Groundwater in the Xongxian geothermal field was recharged by precipitation in the late Pleistocene, whose isotopes are more 
depleted than those in the Holocene.  
Kong et al. 
 5 
(3) The long residence time of more than 30 ka for geothermal water causes to a weak oxygen shift, which implies the occurrence 
of water-rock interaction. 
ACKNOWLEDGEMENTS 
This study is supported by the National Natural Science Foundation of China (Grant 41372257). The authors appreciate the 
International Postdoctoral Exchange Fellowship Program China and Project funded by China Postdoctoral Science Foundation for 
the financial support of this work. 
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Deep groundwater cycle in Xiongxian geothermal field

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Deep groundwater cycle in Xiongxian geothermal field

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