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Geothermal System: Recent Advances and Future Perspectives
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Geothermal System: Recent Advances and Future Perspectives

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Earth Sciences".

Deadline for manuscript submissions: closed (20 February 2025) | Viewed by 8995

Special Issue Editors

Prof. Dr. Hong Li

E-Mail Website
Guest Editor
School of Civil Engineering, Dalian University of Technology, Dalian, China
Interests: artificial geothermal development; migration analysis of soil and groundwater pollutants; reservoir geomechanics; boundary element method; rock mechanics
Dr. Na Wu

E-Mail Website
Guest Editor
State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China
Interests: rock mechanics; geothermal energy exploitation

Special Issue Information

Dear Colleagues,

Geothermal energy has attracted worldwide attention as an important clean and renewable energy option because of its source stability, potential high utilization ratio, low pollution, and widespread distribution. The geothermal source includes the shallow geothermal resource, hydrothermal resource, and hot dry rock (HDR), and there are a variety of systems to exploit them.

In recent decades, although the development of geothermal resources has achieved great development, its commercial development also faces numerous challenges in terms of technology, funding, policy, public acceptance, and other aspects. Consequently, this Special Issue aims to offer a platform for researchers to discuss and exchange their recent advances and future perspectives related to the geothermal system. Original research and review articles on conceptual design, numerical simulation, laboratory testing, and case studies are encouraged. We welcome contributions from all practitioners in this scientific field.

Prof. Dr. Hong Li
Dr. Na Wu
Guest Editors

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Keywords

  • geothermal system
  • geothermal reservoir construction techniques
  • drilling and completion techniques
  • microseismic monitoring techniques
  • optimal design and evaluation
  • heat and mass transfer
  • application of artificial intelligence
  • rock mechanics
  • lifecycle analysis
  • financial, environmental and safety risk assessment in geothermal development
  • numerical simulation of coupled multiphysical fields of geothermal energy extraction processes

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Published Papers (5 papers)

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Research

15 pages, 7059 KiB  
Article
A Dual-Task Approach for Onset Time Picking and the Detection of Microseismic Waveforms Based on Deep Learning
by Hang Zhang, Ruoyu Li, Chunchi Ma, Xiaobing Cheng, Simeng Meng, Zhenxing Huang and Di Li
Appl. Sci. 2024, 14(24), 11689; https://doi.org/10.3390/app142411689 - 14 Dec 2024
Viewed by 889
Abstract
Construction projects in deep underground engineering are associated with the recording of massive amounts of diversified signals during real time and continuous microseismic monitoring given the complexity and specificity of the construction environment. Before the analysis of source information and further prediction of [...] Read more.
Construction projects in deep underground engineering are associated with the recording of massive amounts of diversified signals during real time and continuous microseismic monitoring given the complexity and specificity of the construction environment. Before the analysis of source information and further prediction of possible disasters, it is generally necessary to perform onset time picking and detection of microseismic signals. To improve the accuracy and efficiency of these tasks, this paper proposes an advanced deep dual-task neural network, which sequentially integrates the two processes. In this method, a score map is used to label the onset time of micro-fracture waveforms to improve the picking accuracy. The proposed model can simultaneously handle the onset time picking and detection tasks of microseismic signals to achieve optimal performance. Based on the similarity of data structures, the output from the onset time picking section is imported into the detection section to classify different types of microseismic waveforms. The onset time picking and detection procedures can be seamlessly integrated, where the score map of the onset time can help improve the detection accuracy. The results show that this method has a good performance for the onset time picking and detection of microseismic waveforms that are polluted by noises of various types and intensities. A comparison of the proposed method with existing methods and applications in underground engineering projects helped demonstrate the excellent performance of this method. The proposed approach can accelerate the automatic processing of microseismic signals and has significant potential for the exploration of seismology and earthquake research. Full article
(This article belongs to the Special Issue Geothermal System: Recent Advances and Future Perspectives)
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23 pages, 3076 KiB  
Article
Thermal-Hydraulic-Mechanical Coupling Simulation of CO2 Enhanced Coalbed Methane Recovery with Regards to Low-Rank but Relatively Shallow Coal Seams
by Qianqian Ma, Hong Li, Kun Ji and Fengjun Huang
Appl. Sci. 2023, 13(4), 2592; https://doi.org/10.3390/app13042592 - 17 Feb 2023
Cited by 6 | Viewed by 1736
Abstract
CO2 injection technology into coal seams to enhance CH4 recovery (CO2-ECBM), therefore presenting the dual benefit of greenhouse gas emission reduction and clean fossil energy development. In order to gaze into the features of CO2 injection’s influence on [...] Read more.
CO2 injection technology into coal seams to enhance CH4 recovery (CO2-ECBM), therefore presenting the dual benefit of greenhouse gas emission reduction and clean fossil energy development. In order to gaze into the features of CO2 injection’s influence on reservoir pressure and permeability, the Thermal-Hydraulic-Mechanical coupling mechanism of CO2 injection into the coal seam is considered for investigation. The competitive adsorption, diffusion, and seepage flowing of CO2 and CH4 as well as the dynamic evolution of fracture porosity of coal seams are considered. Fluid physical parameters are obtained by the fitting equation using MATLAB to call EOS software Refprop. Based on the Canadian CO2-ECBM project CSEMP, the numerical simulation targeting shallow low-rank coal is carried out, and the finite element method is used in the software COMSOL Multiphysics. Firstly, the direct recovery (CBM) and CO2-ECBM are compared, and it is confirmed that the injection of CO2 has a significant improvement effect on methane production. Secondly, the influence of injection pressure and temperature is discussed. Increasing the injection pressure can increase the pressure difference in the reservoir in a short time, so as to improve the CH4 production and CO2 storage. However, the increase in gas injection pressure will also lead to the rapid attenuation of near-well reservoir permeability, resulting in the weakening of injection capacity. Also, when the injection temperature increases, the CO2 concentration is relatively reduced, and the replacement effect on CH4 is weakened, resulting in a slight decrease in CBM production and CO2 storage. Full article
(This article belongs to the Special Issue Geothermal System: Recent Advances and Future Perspectives)
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15 pages, 4955 KiB  
Article
Mechanical Models for Comparative Analysis of Failure Characteristics and Groundwater Inrush of Coal Seam Floors
by Chunbo Zhao and Wencheng Song
Appl. Sci. 2022, 12(23), 12164; https://doi.org/10.3390/app122312164 - 28 Nov 2022
Cited by 3 | Viewed by 1442
Abstract
Mining activities conducted above aquifers run the risk of groundwater outburst through fractured floor strata. However, the failure mechanism of the seam floor and the variability in its stability with varying dips remain unclear. Considering the influence of excavation-induced pressure, hydraulic pressure and [...] Read more.
Mining activities conducted above aquifers run the risk of groundwater outburst through fractured floor strata. However, the failure mechanism of the seam floor and the variability in its stability with varying dips remain unclear. Considering the influence of excavation-induced pressure, hydraulic pressure and strata dip, two kinds of analytical models were proposed in this study, which mainly included the hydraulic mechanical model and the key stratum model. These models were applied to comparatively investigate the failure characteristics and inrush risk of horizontal and inclined floors, and then confirmed by numerical simulation. The theoretical calculations reveal that the vertical failure ranges of horizontal and inclined floor strata exhibit approximate “inverted saddle” shapes along the inclination, and have the characteristics of symmetrical distribution and “lower-large/upper-small”, respectively, which is generally consistent with the simulated and measured observations. The theoretical maximum depths of damage within horizontal and inclined floor strata are roughly 12 m and 15 m, slightly lower than the result of numerical simulation. Compared with the remaining horizontal layer, the zone close to the lower boundary of the inclined key strata beneath the goaf incurs the most damage, which corresponds well to the distribution of vertical disturbance ranges. Therefore, the theoretical risk of groundwater outburst from the inclined floor after coal extraction is relatively higher than that from the horizontal floor. The mechanical models established in this study could elucidate the mechanism inducing floor failure and water inrush above a confined aquifer, and thus provide valuable insights for the risk assessment of water-related disasters in underground engineering. Full article
(This article belongs to the Special Issue Geothermal System: Recent Advances and Future Perspectives)
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13 pages, 3976 KiB  
Article
Roles of Normal Stress, Roughness, and Slip Displacement in the Stability of Laboratory Fault in a Sandstone
by Wenming Sun, Yingchun Li, Xiaotian Wu and Chun’an Tang
Appl. Sci. 2022, 12(22), 11434; https://doi.org/10.3390/app122211434 - 11 Nov 2022
Cited by 4 | Viewed by 1729
Abstract
Unstable slip of a fault block is considered to be the main cause of shallow earthquakes. However, the underlying mechanism of the stability-to-instability transition of faults has not been fully understood. Here, we used the stiffness ratio, which is the ratio between the [...] Read more.
Unstable slip of a fault block is considered to be the main cause of shallow earthquakes. However, the underlying mechanism of the stability-to-instability transition of faults has not been fully understood. Here, we used the stiffness ratio, which is the ratio between the shear stiffness of the fault subjected to direct shear and the critical stiffness to evaluate the fault stability degree from stable to unstable slip, and examined the effects of normal stress, roughness, and slip displacement on the fault stability. Our experimental results show that with the increase in slip displacement, the shear stiffness change in stable slip mainly includes four stages, namely “rapid increase–keep unchanged–slow increase–rapid decrease”, and unstable slip tends to occur in the last two stages. This process of shear stiffness change is accelerated by the increase in normal stress and the decrease in fault roughness. Our study reveals that fault stability over slip is mutually dictated by asperity interlocking and wear-induced gouge. Asperity interlocking controls fault stability when the gouge amount is low, whereas the fault gouge prevails with the increased wear of the fault surface since the gouge generated during slip can participate in the subsequent friction process. Thus, we infer that the stable–unstable transition of fault over slip is a spontaneous process due to the interplay of asperity interlocking and wear-induced gouge lubrication. Full article
(This article belongs to the Special Issue Geothermal System: Recent Advances and Future Perspectives)
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24 pages, 5928 KiB  
Article
New Perspectives on Excavation Disturbance Zones: Main Driving Forces
by Xiangyong Kong, Shanyong Wang, Zongwu Song, Chun’an Tang, Chaoyun Yu and Xu Chen
Appl. Sci. 2022, 12(21), 11023; https://doi.org/10.3390/app122111023 - 31 Oct 2022
Viewed by 1701
Abstract
The support theory of the excavation disturbance zone (EDZ) cannot provide an accurate physical explanation or theoretical description of the time-dependent properties required for the development of an EDZ. Therefore, the primary factors that cause the formation of an EDZ should be determined [...] Read more.
The support theory of the excavation disturbance zone (EDZ) cannot provide an accurate physical explanation or theoretical description of the time-dependent properties required for the development of an EDZ. Therefore, the primary factors that cause the formation of an EDZ should be determined to further improve the support theory of the EDZ and grasp the principle underlying the control of the long-term stability of rock masses. Considering the headrace tunnel and nuclear waste repository as the research background, this study aimed to understand the deformation damage evolution process of the surrounding rock after tunnel excavation under different working conditions using the self-developed realistic failure process analysis (RFPA2D) code. The simulation revealed the following. First, an EDZ is formed, although the deformation damage to the surrounding rock is relatively small under the action of environmental factors. Second, under the action of stress in the abovementioned case, the deformation speed, damage degree, and scope of the surrounding rock significantly increase, accelerating the formation and development of the EDZ. Therefore, the boundary of the EDZ expands significantly. Third, when environmental factors are blocked, the range of the EDZ is small due to the small deformation damage to the surrounding rock. Thus, the main factors responsible for the formation of the EDZ are environmental factors, whereas stress is only an auxiliary factor. A numerical simulation method that considers environmental factors can more accurately reproduce the formation of an EDZ. Therefore, a study of the internal mechanism of the EDZ phenomenon can provide a more in-depth understanding of the essential characteristics of an EDZ at the macro level. Furthermore, it can provide a scientific basis and method for the construction and support designs of underground excavation projects and widen the possibilities for further improving the support theory of the EDZ. Full article
(This article belongs to the Special Issue Geothermal System: Recent Advances and Future Perspectives)
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