Deep Underground Science and Engineering最新文献

Deep Underground Science and Engineering (DUSE) publishes this special issue on geothermal energy. The guest editors of this special issue are Prof. Ranjith Pathegama Gamage (Monash University, Australia), Prof. Zhongwei Huang (China University of Petroleum, Beijing, China), and Prof. Bing Bai (Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, China). Geothermal energy is one sustainable and renewable energy and currently a hot research topic in research and development. Geothermal energy supply is one of the long-term efforts for carbon footprint reductions to tackle climate change issues. The development of geothermal energy includes exploration and extraction processes. This special issue is to highlight the challenges on the exploration and extraction of geothermal energy such as initial high cost and difficulties in heat extraction from deep underground. This special issue focuses on new geothermal extraction system, new theory, new technology, new application of latest techniques such as artificial intelligence, and potential environmental effects.

This special issue publishes 10 articles with authors from different countries. An article is contributed by Chinese researchers on the site investigation for geothermal potential evaluation. They propose an integrated geophysics technique by combining multiple geophysics techniques with a new data processing method and apply it to the site investigation of the geothermal potential in a county. A Finnish researcher publishes an article to highlight the challenges and precautionary measures to overcome the difficulties in deep borehole heat exchanges. An article by US researchers explores possible geothermal-mechanical alternations due to heat exchange and extraction in geothermal systems. This article certainly provides new insights into the geothermal energy research and practice. Researchers from Morocco present a status and prospects article on the development of geothermal energy in their country.

Several interesting articles on geothermal reservoirs appear in this issue. A joint multinational research effort by researchers from the United Kingdom, Belgium, China, and Indonesia reports the results of experiments on fluid-rock interaction for potential carbon storage in geothermal reservoirs. Their experimental results have provided some insightful findings on the subject matter. In addition, a group of researchers from China investigates the impact of well placement and flow rate on production efficiency in fractured geothermal reservoirs. Another group of Chinese researchers provides a state-of-the-art review on research and development for the thermal energy extraction from deep hot dry rock reservoirs. These three articles are certainly useful to researchers and engineers in geothermal energy fields.

An article by Chinese researchers reports the development of a thermal stress loading technique for mechanical tests on hot dry rock. Last b

Squeezing phenomena can lead to severe loads in deep tunnels, especially in the presence of a low ratio of surrounding rock strength to overburden pressure. For this reason, it is highly imperative to analyze and identify a suitable methodology to estimate the squeezing potential and select a proper support system of rock mass. This study aims to reveal the causes of failure of Tishreen tunnel in the west of Syria and develop remediation measures accordingly so as to bring the tunnel back into service. The tunnel in question was subjected to successive failures such as buckling and spalling of side walls, floor heave, and extremely large convergence reaching the failure state of the tunnel lining. In this study, an effective way was demonstrated to evaluate the squeezing potential of the tunnel lining and appropriate modeling of the long-term response of a tunnel excavated in weak rock. Specifically, the causes of failure of Tishreen tunnel were first evaluated by empirical approaches. Then, a numerical model was developed using a time-dependent constitutive model to investigate the time-dependent response of the tunnel lining. On this basis, this study proposed an effective reinforcement schemes including steel ribs, grout injection, ground anchors, and new lining of reinforced concrete. The results show that the Burger viscoplastic model simulates effectively the resulting deformation and creep behavior of squeezing ground. It is also observed that using a combined heavy support system can provide efficient control over squeezing deformation and maintain the serviceability of the tunnel under study.

In the last few decades, addressing the global challenge of implementation of strategies for renewable energy and energy efficiency has become crucial. Morocco, since 2009, has made a steadfast commitment to sustainability, with a particular focus on advancing the development of renewable energy resources. A comprehensive strategy has been formulated, centering on utilizing the country's energy potential to drive progress in this vital sector. Morocco is considered a country with abundant thermal water, indicating deep reservoirs with significant hydrothermal potential. Geothermal zones were selected based on the abundance of hot springs where water temperatures were high and geothermal gradients were significant. The abundance and importance of hot springs, combined with recent volcanism and ongoing non-tectonic activity linked to alpine orogeny, strongly suggest that these regions are promising reservoirs for geothermal energy. This great potential also extends to neighboring countries. In northeast and south Morocco, the temperature of thermal water ranges from 26 to 54°C. This study serves as an inclusive review of the geothermal potentialities in Morocco.

The 10 000-m ultradeep dolomite reservoir holds significant potential as a successor field for future oil and gas exploration in China's marine craton basin. However, major challenges such as the genesis of dolomite, the formation time of high-quality reservoirs, and the preservation mechanism of reservoirs have always limited exploration decision-making. This research systematically elaborates on the genesis and reservoir-forming mechanisms of Sinian–Cambrian dolomite, discussing the ancient marine environment where microorganisms and dolomite develop, which controls the formation of large-scale Precambrian–Cambrian dolomite. The periodic changes in Mg isotopes and sedimentary cycles show that the thick-layered dolomite is the result of different dolomitization processes superimposed on a spatiotemporal scale. Lattice defects and dolomite embryos can promote dolomitization. By simulating the dissolution of typical calcite and dolomite crystal faces in different solution systems and calculating their molecular weights, the essence of heterogeneous dissolution and pore formation on typical calcite and dolomite crystal faces was revealed, and the mechanism of dolomitization was also demonstrated. The properties of calcite and dolomite (104)/(110) grain boundaries and their dissolution mechanism in carbonate solution were revealed, showing the limiting factors of the dolomitization process and the preservation mechanism of deep buried dolomite reservoirs. The in situ laser U-Pb isotope dating technique has demonstrated the timing of dolomitization and pore formation in ancient carbonate rocks. This research also proposed that dolomitization occurred during the quasi-contemporaneous or shallow-burial periods within 50 Ma after deposition and pores formed during the quasi-contemporaneous to the early diagenetic periods. And it was clear that the quasi-contemporaneous dolomitization was the key period for reservoir formation. The systematic characterization of the spatial distribution of the deepest dolomite reservoirs in multiple sets of the Sinian and the Cambrian in the Chinese craton basins provides an important basis for the distribution prediction of large-scale dolomite reservoirs. It clarifies the targets for oil and gas exploration at depths over 10 000 m. The research on dolomite in this study will greatly promote China's ultradeep oil and gas exploration and lead the Chinese petroleum industry into a new era of 10 000-m deep oil exploration.

Assessing the stability of pillars in underground mines (especially in deep underground mines) is a critical concern during both the design and the operational phases of a project. This study mainly focuses on developing two practical models to predict pillar stability status. For this purpose, two robust models were developed using a database including 236 case histories from seven underground hard rock mines, based on gene expression programming (GEP) and decision tree-support vector machine (DT-SVM) hybrid algorithms. The performance of the developed models was evaluated based on four common statistical criteria (sensitivity, specificity, Matthews correlation coefficient, and accuracy), receiver operating characteristic (ROC) curve, and testing data sets. The results showed that the GEP and DT-SVM models performed exceptionally well in assessing pillar stability, showing a high level of accuracy. The DT-SVM model, in particular, outperformed the GEP model (accuracy of 0.914, sensitivity of 0.842, specificity of 0.929, Matthews correlation coefficient of 0.767, and area under the ROC of 0.897 for the test data set). Furthermore, upon comparing the developed models with the previous ones, it was revealed that both models can effectively determine the condition of pillar stability with low uncertainty and acceptable accuracy. This suggests that these models could serve as dependable tools for project managers, aiding in the evaluation of pillar stability during the design and operational phases of mining projects, despite the inherent challenges in this domain.

The corrosion of waste canisters in the deep geological disposal facilities (GDFs) for high-level radioactive waste (HLRW) can generate gas, which escapes from the engineered barrier system through the interfaces between the bentonite buffer blocks and the host rock and those between the bentonite blocks. In this study, a series of water infiltration and gas breakthrough experiments were conducted on granite and on granite–bentonite specimens with smooth and grooved interfaces. On this basis, this study presents new insights and a quantitative assessment of the impact of the interface between clay and host rock on gas transport. As the results show, the water permeability values from water infiltration tests on granite and granite–bentonite samples (10⁻¹⁹–10⁻²⁰ m²) are found to be slightly higher than that of bentonite. The gas permeability of the mock-up samples with smooth interfaces is one order of magnitude larger than that of the mock-up with grooved interfaces. The gas results of breakthrough pressures for the granite and the granite–bentonite mock-up samples are significantly lower than that of bentonite. The results highlight the potential existence of preferential gas migration channels between the rock and bentonite buffer that require further considerations in safety assessment.

The flow characteristics of coalbed methane (CBM) are influenced by the coal rock fracture network, which serves as the primary gas transport channel. This has a significant effect on the permeability performance of coal reservoirs. In any case, the traditional techniques of coal rock fracture observation are unable to precisely define the flow of CBM. In this study, coal samples were subjected to an in situ loading scanning test in order to create a pore network model (PNM) and determine the pore and fracture dynamic evolution law of the samples in the loading path. On this basis, the structural characteristic parameters of the samples were extracted from the PNM and the impact on the permeability performance of CBM was assessed. The findings demonstrate that the coal samples' internal porosity increases by 2.039% under uniaxial loading, the average throat pore radius increases by 205.5 to 36.1 μm, and the loading has an impact on the distribution and morphology of the pores in the coal rock. The PNM was loaded into the finite element program COMSOL for seepage modeling, and the M3 stage showed isolated pore connectivity to produce microscopic fissures, which could serve as seepage channels. In order to confirm the viability of the PNM and COMSOL docking technology, the streamline distribution law of pressure and velocity fields during the coal sample loading process was examined. The absolute permeability of the coal samples was also obtained in order for comparison with the measured results. The macroscopic CBM flow mechanism in complex low-permeability coal rocks can be revealed through three-dimensional reconstruction of the microscopic fracture structure and seepage simulation. This study lays the groundwork for the fine description and evaluation of coal reservoirs as well as the precise prediction of gas production in CBM wells.

Fracture surface contour study is one of the important requirements for characterization and evaluation of the microstructure of rocks. Based on the improved cube covering method and the 3D contour digital reconstruction model, this study proposes a quantitative microstructure characterization method combining the roughness evaluation index and the 3D fractal dimension to study the change rule of the fracture surface morphology after blasting. This method was applied and validated in the study of the fracture microstructure of the rock after blasting. The results show that the fracture morphology characteristics of the 3D contour digital reconstruction model have good correlation with the changes of the blasting action. The undulation rate of the three-dimensional surface profile of the rock is more prone to dramatic rise and dramatic fall morphology. In terms of tilting trend, the tilting direction also shows gradual disorder, with the tilting angle increasing correspondingly. All the roughness evaluation indexes of the rock fissure surface after blasting show a linear and gradually increasing trend as the distance to the bursting center increases; the difference between the two-dimensional roughness evaluation indexes and the three-dimensional ones of the same micro-area rock samples also becomes increasingly larger, among which the three-dimensional fissure roughness coefficient JRC and the surface roughness ratio R_s display better correlation. Compared with the linear fitting formula of the power function relationship, the three-dimensional fractal dimension of the postblast fissure surface is fitted with the values of JRC and R_s, which renders higher correlation coefficients, and the degree of linear fitting of JRC to the three-dimensional fractal dimension is higher. The fractal characteristics of the blast-affected region form a unity with the three-dimensional roughness evaluation of the fissure surface.

In view of the limited theoretical research on the load model of initial support for horseshoe-shaped prefabrication, this study focuses on the Luochuan Tunnel on the Xi'an-Yan'an newly built railway as the research object to explore its load model, load characteristic curve, plastic zone, deformation, and critical thickness. Theoretical research and numerical analysis were conducted. The results indicate that under the same boundary conditions, the ultimate bearing capacity of the prefabricated assembly initial support is higher than that of the shotcrete initial support, resulting in larger ultimate deformation capacity of the prefabricated assembly initial support. Based on numerical calculations, the ultimate deformation and critical thickness of the prefabricated initial lining for single- and double-track railway tunnels are obtained when buried at depths of 200, 500, and 900 m in rock masses of classes III, IV, and V.

Geothermal energy from deep underground (or geological) formations, with or without its combination with carbon capture and storage (CCS), can be a key technology to mitigate anthropogenic greenhouse gas emissions and meet the 2050 net-zero carbon emission target. Geothermal resources in low-permeability and medium- and high-temperature reservoirs in sedimentary sequence require hydraulic stimulation for enhanced geothermal systems (EGS). However, fluid migration for geothermal energy in EGS or with potential CO₂ storage in a CO₂-EGS are both dependent on the in situ flow pathway network created by induced fluid injection. These thermo-mechanical interactions can be complex and induce varying alterations in the mechanical response when the working fluid is water (in EGS) or supercritical CO₂ (in CO₂-EGS), which could impact the geothermal energy recovery from geological formations. Therefore, there is a need for a deeper understanding of the heat extraction process in EGS and CO₂-EGS. This study presents a systematic review of the effects of changes in mechanical properties and behavior of deep underground rocks on the induced flow pathway and heat recovery in EGS reservoirs with or without CO₂ storage in CO₂-EGS. Further, we proposed waterless-stimulated EGS as an alternative approach to improve heat energy extraction in EGS. Lastly, based on the results of our literature review and proposed ideas, we recommend promising areas of investigation that may provide more insights into understanding geothermo-mechanics to further stimulate new research studies and accelerate the development of geothermal energy as a viable clean energy technology.