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Advances in the Utilization of Underground Energy and Space

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "H: Geo-Energy".

Deadline for manuscript submissions: closed (8 September 2023) | Viewed by 13417

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Special Issue Editors

Dr. Wei Liu

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Guest Editor

School of Resources and Safety Engineering, Chongqing University, Chongqing, 400044, China
Interests: energy (oil/gas/hydrogen/CO2) storage in underground space; coal bed methane exploration; mining economy and investment
Special Issues, Collections and Topics in MDPI journals

Dr. Jifang Wan

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School of Mechanical Engineering, Yangtze University, Jingzhou 434023, China
Interests: underground energy storage; unconventional oil and gas drilling and completion; downhole tools
Special Issues, Collections and Topics in MDPI journals

Dr. Yun Yang

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Guest Editor

Tight Oil Consortium, Department of Geoscience, University of Calgary, Calgary, AB 2500, Canada,
Interests: geological carbon sequestration; reservoir simulation; gas adsorption modeling and experiments; nanopores characterization

Special Issue Information

Dear Colleagues,

Most fossil fuels (coal, oil, gas, etc.) are obtained from underground reservoirs in the crust of the Earth. The utilization of underground energy and space is important for humans. With the globally recognized target of carbon neutralization and carbon peak, the question of how to efficiently utilize underground energy and space has become a hotpot and focus in the study of science and engineering. The processes of fossil fuel exploration and development are associated with geophysics, rock mechanics, drilling engineering, computing science and mechanical engineering, etc. After the underground space is formed by artificial process or natural ways, the space is usually used for underground energy storage, CCS and CCUS, waste disposal, resource recovery, etc. The status quo of the processes has contributed to the advances in materials, design methodologies, modelling tools and practice experiences. Moreover, the total process has pushed forward the research in the areas of geo-tectonics, underground technologies, environments, multi-coupling and engineering management, leading to the development of more reliable simulation, design and management in the utilization regions of underground energy and space.

This Special Issue aims to present and disseminate the most recent advances related to the theory, design, modelling, tools, application and engineering practices of all the topics associated with the utilization of the underground energy and space.

Topics of interest for publication include, but are not limited to:

All aspects of underground energy storage, including salt cavern energy storage, pumped storage power stations, compressed air energy storage in underground space, and depleted reservoir gas storage.
CCS or CCUS in aquifers, salt caverns, depleted reservoirs, coal beds, shale fracturing, and others.
Utilization of abandoned underground mining space.
Theory, technologies, tools, modelling methods, and field applications of unconventional gas exploration and development.
Construction theory and technologies of underground space for utilization.
Safety and economic evaluations for underground space and energy utilization.
Other topics related to the Special Issue.

Dr. Wei Liu
Dr. Jifang Wan
Dr. Yun Yang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

underground energy storage
CCS and CCUS in underground space
utilization of underground mining space
unconventional gas exploration and development

Published Papers (11 papers)

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Research

22 pages, 7086 KiB

Open AccessArticle

Feasibility Analysis of Compressed Air Energy Storage in Salt Caverns in the Yunying Area

by Jinrong Mou, Haoliang Shang, Wendong Ji, Jifang Wan, Taigao Xing, Hongling Ma and Wei Peng

Energies 2023, 16(20), 7171; https://doi.org/10.3390/en16207171 - 20 Oct 2023

Viewed by 704

Abstract

With the widespread recognition of underground salt cavern compressed air storage at home and abroad, how to choose and evaluate salt cavern resources has become a key issue in the construction of gas storage. This paper discussed the condition of building power plants, the collection of regional data and salt plant data, and the analysis of stability and tightness. Comprehensive analysis and evaluation methods were put forward from four aspects, including ground comprehensive conditions, regional geological conditions and formation lithology, salt mine characteristics, stability, and tightness of salt caverns. The limit equilibrium theory was applied to establish the limit equilibrium failure mode of salt caverns under operating pressure, and the stability coefficient calculation method of the target salt cavern was determined by combining the mechanical characteristics. Based on the physical and mechanical properties of salt rocks, it was found that salt rocks with enough thickness around the salt cavity could be used as sealing rings to ensure the tightness of the salt cavern. Combined with the field water sealing test, the tightness of the target salt cavern is verified. This method has been applied to the salt cavern screening and evaluation of a 300 MW compressed air energy storage power plant project in Yingcheng, Hubei Province, and remarkable results have been obtained, indicating the rationality of the method. Full article

(This article belongs to the Special Issue Advances in the Utilization of Underground Energy and Space)

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14 pages, 13872 KiB

Open AccessArticle

Pitting and Strip Corrosion Influence on Casing Strength of Salt Cavern Compressed Air Energy Storage

by Jifang Wan, Wendong Ji, Yuxian He, Jingcui Li and Ye Gao

Energies 2023, 16(14), 5362; https://doi.org/10.3390/en16145362 - 14 Jul 2023

Viewed by 821

Abstract

In response to the localized corrosion generated by underground casing, which seriously affects the safe operation of salt cavern compressed air storage, we used commercial finite element software, ANSYS, to propose a partial model applicable to casings with pitting and strip corrosion. The results show that the pitting depth of the casing is closely related to fracture and collapse pressure. As pitting corrosion depth increases, its effect on fracture and collapse pressure becomes more significant. The greater the number of corrosion pits, the lower the compressive strength of the casing, and the casing tends to be more prone to fracture. The area with large stress is mainly distributed along the long axis of the strip corrosion. In the short axis of the strip corrosion, there is no stress concentration and appears as a low stress region. The effect of strip corrosion depth on failure pressure is greater than the effect of strip corrosion length. In this work, we developed a method to predict residual strength, which is useful to assess not only well integrity but, additionally, safety of the casing used during petroleum and natural gas exploration and production. Full article

(This article belongs to the Special Issue Advances in the Utilization of Underground Energy and Space)

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16 pages, 8455 KiB

Open AccessArticle

Experimental Study of the Shear Characteristics of Fault Filled with Different Types of Gouge in Underground Gas Storage

by Guosheng Ding, Hejuan Liu, Debin Xia, Duocai Wang, Famu Huang, Haitao Guo, Lihuan Xie, Yintong Guo, Mingyang Wu and Haijun Mao

Energies 2023, 16(7), 3119; https://doi.org/10.3390/en16073119 - 29 Mar 2023

Viewed by 1032

Abstract

In the current international situation, energy storage is an important means for countries to stabilize their energy supply, of which underground storage of natural gas is an important part. Depleted gas reservoir type underground gas storage (UGS) has become the key type of gas storage to be built by virtue of safety and environmental protection and low cost. The multi-cycle high injection and production rate of natural gas in the depleted gas reservoir type UGS will cause the in-situ stress disturbance. The slip risk of fault in the geological system increases greatly compared with that before the construction of the storage engineering, which becomes a great threat to the sealing of the gas storage. Reasonable injection and production strategy depend on the reliable assessment of the shear behavior of the fault belt, which can guarantee the sealing characteristics of the UGS geological system and the efficient operation of the UGS. Therefore, the shear behavior of the fault is studied by carrying out experiments, which can provide important parameters for the evaluation of fault stability. However, there is a large gap between the rock samples used in the previous experimental study and the natural faults, and it is difficult to reflect the shear failure characteristics of natural faults. In this paper, similar fault models based on high-precision three-dimensional scanners and engraving machines, filled with three types of fault gouge, are prepared for a batch of representative direct shear tests. The results show that the peak shear strength of the fault rocks with a shear surface is higher than that of the fault rocks with a tensile surface. Compared with the clay mineral content, the roughness of the fault surface is much more significant for the shear strength of the fault rock. For the fault rocks with similar fault surface morphology, the higher the clay content in the fault gouge, the greater the shear strength of the fault rocks. For the fault rocks with different fault surface morphology and the same fault gouge, the cohesion and internal friction angle of the tensile type is generally smaller than that of the shear type. Full article

(This article belongs to the Special Issue Advances in the Utilization of Underground Energy and Space)

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15 pages, 1982 KiB

Open AccessArticle

A Feasibility Study on Gravity Power Generation Technology by Virtue of Abandoned Oil-Gas Wells in China

by Jingcui Li, Jifang Wan, Yan Xia, Sixiang Zhao, Guowei Song and Yuxian He

Energies 2023, 16(4), 1575; https://doi.org/10.3390/en16041575 - 04 Feb 2023

Cited by 1 | Viewed by 1814

Abstract

In the future, there will be more and more abandoned oil-gas wells with the exploitation of onshore oilfield resources. However, the large height difference in abandoned oil-gas wells can be used as building blocks for gravity power generation, thus maximizing the economic value of abandoned oil-gas wells. In this study, a scheme of gravity power generation by virtue of the spud-in casing depth of oil-gas wells is proposed, and a gravity power generation model based on abandoned oil-gas wells is established. The parameters and economic benefits of gravity energy storage are calculated for oil-gas wells in the Huabei oilfield, the Daqing oilfield, and the Xinjiang oilfield. It is shown that the power density and discharge time of the gravity energy storage system in abandoned oil-gas wells are suitable for distributed power generation. In addition, the fast response characteristics of energy storage in abandoned oil-gas wells are verified, which makes the system suitable for correcting continuous and sudden frequency and voltage changes in the power grid but not suitable for energy arbitrage under a high number of annual cycles. Furthermore, the leveling cost of storage of the gravity system in abandoned oil-gas wells is more economical with the high number of annual cycles. The analysis of this work provides a significant investigation of the feasibility of gravity power generation by using abandoned oil-gas wells. Full article

(This article belongs to the Special Issue Advances in the Utilization of Underground Energy and Space)

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15 pages, 6990 KiB

Open AccessArticle

Characteristics of High Flow Zones and a Balanced Development Strategy of a Thick Bioclastic Limestone Reservoir in the Mishrif Formation in X Oilfield, Iraq

by Fengfeng Li, Lei Li and Jiaheng Chen

Energies 2023, 16(3), 1451; https://doi.org/10.3390/en16031451 - 01 Feb 2023

Viewed by 1084

Abstract

The Mishrif Formation in X Oilfield in Iraq is heterogeneous and has prominent development contradictions, and the development plan required urgent adjustment. Based on data regarding the core, cast thin sections, physical property, mercury injection experiments, and development performance, the main geological factors causing the unbalanced development of the Mishrif Formation are identified, and the corresponding development strategy is proposed. The results show that the High Flow Zones (HFZs) are the main geological factors causing unbalanced production in the thick bioclastic limestone reservoir. There are three kinds of HFZs in MA, MB1, and MB2 intervals, namely, the point shoal type, the tidal channel type, and the platform margin shoal type. All HFZs have different scales and distribution patterns. HFZs have ultra-high permeability and large permeability differences with the surrounding reservoir. During development, the oil mainly comes from HFZs, and the considerable reserves in the low permeability reservoir surrounding the HFZs are difficult to develop. The size of the pore throat of the HFZs greatly varies, and permeability is mainly dominated by the mega-pore throat (>10 μm) and the macro-pore throat (2.5~10 μm). In water flood development, the injected water rapidly advances along the mega-pore throat and the macro-pore throat, and the oil in the micro-pore or medium-pore throats are difficult to be displace. It can be concluded that the Mishrif Formation is vertically heterogeneous. The connectivity of HFZs in different intervals greatly varies. As a result, the Mishrif Formation is divided into three development units, MA, MB1, and MB2 + MC, and production wells are deployed in HFZs. The MA adopts a reverse nine-point injection-production pattern, for which the well spacing is 900 m using a vertical well, and the injection well should avoid the HFZs near the faults. The MB1 adopts an irregular five-point injection-production pattern using a vertical well, and the injection wells are deployed at the edge of the tidal channel or in the lagoon. MB2_1 deploys horizontal production wells, for which the well spacing is 900 m. Horizontal production wells, for which the well spacing is 300 m, are deployed in the lower MB2, and the lateral horizontal production wells are converted into injection wells after water breakthrough, and the horizontal wells deployed in the lower part of MC should moderately inject water. Full article

(This article belongs to the Special Issue Advances in the Utilization of Underground Energy and Space)

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21 pages, 6053 KiB

Open AccessArticle

Production Forecasting Based on Attribute-Augmented Spatiotemporal Graph Convolutional Network for a Typical Carbonate Reservoir in the Middle East

by Meng Gao, Chenji Wei, Xiangguo Zhao, Ruijie Huang, Jian Yang and Baozhu Li

Energies 2023, 16(1), 407; https://doi.org/10.3390/en16010407 - 29 Dec 2022

Cited by 2 | Viewed by 1249

Abstract

Production forecasting plays an important role in development plans during the entire period of petroleum exploration and development. Artificial intelligence has been extensively investigated in recent years because of its capacity to extensively analyze and interpret complex data. With the emergence of spatiotemporal models that can integrate graph convolutional networks (GCN) and recurrent neural networks (RNN), it is now possible to achieve multi-well production prediction by considering the impact of interactions between producers and historical production data simultaneously. Moreover, an accurate prediction not only depends on historical production data but also on the influence of neighboring injectors’ historical gas injection rate (GIR). Therefore, based on the assumption that introducing GIR can enhance prediction accuracy, this paper proposes a deep learning-based hybrid production forecasting model that is aimed at considering both the spatiotemporal characteristics of producers and the GIR of neighboring injectors. Specifically, we integrated spatiotemporal characteristics and GIR into an attribute-augmented spatiotemporal graph convolutional network (AST-GCN) and gated recurrent units (GRU) neural network to extract intricate temporal correlations from historical data. The method proposed in this paper has been successfully applied in a well pattern (including five producers and seven gas injectors) in a low-permeability carbonate reservoir in the Middle East. In single well production forecasting, the error of AST-GCN is 63.2%, 37.3%, and 16.1% lower in MedAE, MAE, and RMSE compared with GRU and 62.9%, 44.6%, and 28.9% lower compared with RNS. Similarly, the accuracy of AST-GCN is 15.9% and 35.8% higher than GRU and RNS in single well prediction. In well-pattern production forecasting, the error of AST-GCN is 41.2%, 64.2%, and 75.2% lower in RMSE, MAE, and MedAE compared with RNS, while the accuracy of AST-GCN is 29.3% higher. After different degrees of Gaussian noise are added to the actual data, the average change in AST-GCN is 3.3%, 0.4%, and 1.2% in MedAE, MAE, and RMSE, which indicates the robustness of the proposed model. The results show that the proposed model can consider the production data, gas injection data, and spatial correlation at the same time, which performs well in oil production forecasts. Full article

(This article belongs to the Special Issue Advances in the Utilization of Underground Energy and Space)

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26 pages, 26405 KiB

Open AccessArticle

Coalbed Methane Reservoir Parameter Prediction and Sweet-Spot Comprehensive Evaluation Based on 3D Seismic Exploration: A Case Study in Western Guizhou Province, China

by Yuanlong Wei, Lingyun Zhao, Wei Liu, Xiong Zhang, Zhijun Guo, Zhangli Wu and Shenghui Yuan

Energies 2023, 16(1), 367; https://doi.org/10.3390/en16010367 - 28 Dec 2022

Cited by 3 | Viewed by 1156

Abstract

As a kind of clean energy, the exploration and development of coalbed methane (CBM) are of great importance and significance. In this paper, the CBM reservoir parameters of a working area in Western Guizhou Province, China, were predicted by using 3D seismic exploration technology, and the sweet-spot area was evaluated based on the prediction results. In terms of data interpretation, while the traditional technology is extended to the study of CBM, new technologies and methods suitable for CBM were also actively explored, especially in the quantitative prediction methods of parameters such as coal seam thickness, CBM content, coal body structure, in situ stress, etc., and a three-highs quantitative prediction technology of CBM sweet spots characterized by high precision, high resolution, and high coincidence was explored, which is based on logging evaluation and petrophysics. In addition, in the comprehensive evaluation of multiparameter sweet spots, the multiparameter weighted step-by-step evaluation method based on inversion was innovatively proposed, which made the prediction of CBM sweet spots more focused, effective, and practical, and the distribution law of sweet spots was more consistent with the geological law, providing enough basis for subsequent well location deployment. Based on this method, the C409 coal seam was selected as the sweet spot. Full article

(This article belongs to the Special Issue Advances in the Utilization of Underground Energy and Space)

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17 pages, 7644 KiB

Open AccessArticle

Experimental Study on Shear Characteristics of Structural Plane with Different Fluctuation Characteristics

by Yintong Guo, Qiqi Ying, Duocai Wang, Hong Zhang, Famu Huang, Haitao Guo, Lei Hou, Mingnan Xu, Hejuan Liu and Debin Xia

Energies 2022, 15(20), 7563; https://doi.org/10.3390/en15207563 - 13 Oct 2022

Cited by 2 | Viewed by 1053

Abstract

With the increasing scale and depth of underground engineering, the geological environment that engineering is faced with is becoming more complex. As the weak position of rock mass, the structural surface has a particularly great influence on the mechanical characteristics of the rock mass. In order to obtain the shear strength characteristic of the structural plane and analyze the influence of morphological parameters such as the undulating angle and bulge degree on shearing, taking medium-low permeability tight sandstone as the research object, four kinds of structural plane samples with different undulating angles (10, 20, 30 and 40°) were prepared with a Python and high-precision engraving machine. Direct shear tests under different normal stresses (2, 4, 6 and 8 MPa) and shear rates (0.6, 1.2 and 2.4 mm/min) were performed, and the shear mechanical properties were analyzed. The structural surfaces before and after shearing were scanned using a high-precision three-dimensional scanner, so as to evaluate the roughness of the structural surface and determine the influence from various factors on the shear characteristics. The test results showed that for the structural plane with the same undulating angle, the peak shear stress increased approximately linearly with an increase in normal stress at a 0.6 mm/min shear rate and an increment speed of approximately 0.82, while the peak shear stress negatively correlated with the shear rate at a value of 4 MPa for normal stress. The larger the undulating angle was, the greater the influence of the shear rate (the shear stress decreased by 2.31 MPa at a 40° angle). When the normal stress and the shear rate were fixed, the peak shear stress corresponding to the structural surface gradually increased with the increase in the undulating angle, and the maximum increment was 5.04 MPa at 4 MPa normal stress and a 0.6 mm/min shear rate. An analysis of the morphological characteristics of the structural plane showed that when the undulating angle (40°) and the normal stress (6 and 8 MPa) were larger, the damage of the structural plane became more obvious, the shear point was closer to the tooth valley position, and the mechanical bite force and friction force of the structural plane were better utilized. When the shear rate was lower (0.6 mm/min), the friction characteristics of the shear surface were more visible, the shear was increasingly sufficient, and the corresponding shear strength was also greater. Full article

(This article belongs to the Special Issue Advances in the Utilization of Underground Energy and Space)

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16 pages, 6062 KiB

Open AccessArticle

Experimental Investigation on the Evolution of Tensile Mechanical Behavior of Cement Stone Considering the Variation of Burial Depth

by Bohang Liu, Lei Wang, Yintong Guo, Jing Li and Hanzhi Yang

Energies 2022, 15(19), 7340; https://doi.org/10.3390/en15197340 - 06 Oct 2022

Viewed by 957

Abstract

The cement sheath is an annular structure between casing and formation, which is crucial to the integrity of the wellbore system. Considering that the temperature and pressure environment is changing continuously with increasing burial depth, the micro-structure and macro=mechanical properties of the in-situ cement sheath will change accordingly. To investigate the variation of burial depth on the evolution of the tensile mechanical behavior of oil cement stone, five temperature-pressure curing and testing conditions (25 °C—0 MPa, 50 °C—10 MPa, 80 °C—20 MPa, 110 °C—30 MPa, and 140 °C—40 MPa) are set to approximately simulate an in situ temperature-pressure environment at five typical burial depths (0 m, 1000 m, 2000 m, 3000 m, and 4000 m). The in situ tensile behavior, micro-structure and pore size distribution of the cement stones at each condition are tested and comparatively analyzed. Results show that with increasing temperature and pressure, the brittleness of the cement stone reduces and its ductility strengthens accordingly. The tensile strength experiences rapid growth at first, then increases at a slower rate and finally decreases. The failure mode of the cement stone gradually transforms from tensile splitting to tensile-shear composite fracture, accompanied by increasing fracture surface roughness. Microscopically, with increasing curing temperature and pressure, the pore structure of cement stone gradually transforms from closely stacked laminated sheets to interconnected fiber networks. The dense structure of cement stone gradually becomes loose and porous. The porosity also increases from 15.96% to 29.46%. Full article

(This article belongs to the Special Issue Advances in the Utilization of Underground Energy and Space)

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20 pages, 4640 KiB

Open AccessArticle

Evaluation of Long-Term Tightness of the Coal Pillar Dam of Underground Reservoir and Protection Countermeasures

by Zhixin Zhang, Qiang Guo and Wei Liu

Energies 2022, 15(19), 7229; https://doi.org/10.3390/en15197229 - 01 Oct 2022

Cited by 4 | Viewed by 1152

Abstract

The coal mine underground reservoir is an effective facility for mine groundwater utilization in water-deficient and ecologically fragile areas. Usually, the artificial reserved coal pillar is used as the dam of underground reservoir, and little research has been done on its tightness performance. Comsol software is used to simulate the leakage of underground reservoirs in Shendong area, in the western part of China, and the long-term tightness of coal pillar dam under different operation conditions is evaluated. The results show that: (1) When the underground reservoir is not connected with the upper water system, the coal pillar dam has good tightness performance. When they are connected, the leakage of reservoir increased due to the raised water level, and the deeper the burial depth, the greater the leakage amount. (2) When reservoir is pumping and storing water, the leakage is only half of that under constant water pressure storage, indicating that this operation mode is beneficial to the long-term tightness of a coal pillar dam. (3) With the increase of the permeability of a coal pillar dam, the leakage will be aggravated. It is suggested that the permeability of a coal pillar dam should not exceed 1 × 10⁻¹⁵ m². (4) The tightness of the coal pillar dam damaged by brine immersion is greatly reduced. With only 3 m of soaking damage distance, the total leakage is twice that of the undamaged one. For a coal pillar dam with poor tightness, some protection countermeasures are proposed to reduce the reservoir water level or improve the anti-seepage performance of a coal pillar dam, so as to ensure the long-term tightness of the dam. This research can provide theoretical support and technical guidance for evaluating the seepage stability of a coal pillar dam in an underground reservoir and strengthening its seepage control. Full article

(This article belongs to the Special Issue Advances in the Utilization of Underground Energy and Space)

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17 pages, 10894 KiB

Open AccessArticle

Experimental Study on the Compressive and Shear Mechanical Properties of Cement–Formation Interface Considering Surface Roughness and Drilling Mud Contamination

by Lei Wang, Bohang Liu, Hanzhi Yang, Yintong Guo, Jing Li and Hejuan Liu

Energies 2022, 15(17), 6472; https://doi.org/10.3390/en15176472 - 05 Sep 2022

Viewed by 1193

Abstract

In a casing-cement sheath-formation system, the cement–formation interface is usually weakly cemented for the residual of drilling mud, in which a leakage path would easily form, threatening the safe operation of underground energy exploitation and storage. To evaluate the compressive and shear mechanical behavior of the cement–formation interface, cement–rock composite cylindrical specimens were prepared. Uniaxial and triaxial compression and direct shear tests were implemented. The flushing efficiency of the rock surface, compressive strength, interface incompatible deformation, parameters of shear strength, and morphology of shear failure surface were acquired and analyzed. Results show that the flushing efficiency of shale surface decreases from 76.7% to 64.2% with the surface roughness increasing from 0 to 2 mm. The flushing efficiency of sandstone is only 44.7%, remarkably lower than that of shale. With the stress condition transforming from uniaxial to triaxial compression, the feature of the stress–strain curves changes from elastic-brittle to elastoplastic, and the compressive strength increases from 20.6~60.1 MPa to 110~120 MPa. The cement part presents noteworthy plastic deformation and several micro shear fractures develop. There is incompatible deformation between cement and rock, which induces interface debonding for almost all the composite specimens. The internal friction angle and cohesive strength both decrease with the increase in pollution degree of drilling mud, and increase with the rise in surface roughness. The shear facture surface is not exactly the rock–cement interface, but usually manifests as a shear zone, in which the rock, cement, and interface all contribute to the final shear failure. The above findings would be valuable for the revealing of cement–formation interface failure mechanism. Full article

(This article belongs to the Special Issue Advances in the Utilization of Underground Energy and Space)

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