bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rock Mass Failure and Remedial Measures Implemented When Excavating Ultra-Deep Shaft Stations
Authors: Lindsay J. , Hall A. , Cai M. , Simser B. 
Published: August 2024

ABSTRACT:
This paper presents several geotechnical challenges experienced while excavating two shaft stations at the depths of 2490 m and 2550 m in highly stressed grounds, along with engineering solutions that effectively reduce exposure and risk associated with the excavations. Proactive measures were completed ahead of beginning the 2490 shaft station excavation; however, adverse conditions further influenced by a nearby fault led to significant rock mass failure and bowling of the station floor. These unanticipated conditions resulted in project delays and increased risk for the operators working at the face. Based on detailed field observations made while excavating the 2490 shaft station, insights from instrumentation and microseismic monitoring data, the methodology for excavating the 2550 shaft station was modified to mitigate the risk of ground failure. Engineering-based modifications introduced for the 2550 station included reducing the size of the initial shaft station blast, and pre-sinking and supporting the shaft below the station floor before the excavation of the shaft station. These modifications and increased distance from the fault resulted in better control of the ground conditions, leading to a 50% reduction in seismic activity and rockburst risk, and no bowling of the station floor. The outcomes not only resulted in cost savings but also provided valuable insights into the geotechnical intricacies and excavation strategies essential for safe mining operations at extreme depths.

1. INTRODUCTION
In the underground mining industry, many operations use shafts to access orebodies. A shaft is a vertical or inclined excavation sunk from the surface or underground. When a shaft is sunk from underground, it is called an internal winze. Operations that utilize shaft infrastructure require the construction of shaft stations. A shaft and its connecting shaft stations are critical infrastructures that provide access for personnel, equipment, material, and the transportation of ore to the surface.
(McCarthy & Livingstone, 1993) determined that a shaft is a more viable option over a haulage ramp when the depth is greater than 650 m and the production approaches 1.2 million tonnes per year. To access deep ore deposits, a ramp is inherently slower and requires the removal of more waste rock than shaft sinking.
Proppant Migration and Distribution Simulation in Tortuous Fractures with Gradually Narrowing Walls
Authors: Yan Pengyin , Wang Zhiming 
Published: August 2024

ABSTRACT:
Migration and packing patterns of proppants play a critical role in the conductivity of hydraulic fractures and unconventional oil and gas production. However, the fracture surface is usually tortuous with gradually narrow walls (tortuous - wedge fractures). Existing fracture models only consider tortuosity, and more efforts are needed in this regard. In this study, a numerical model of proppant transport in tortuous wedge-shaped fractures is established based on CFD-DEM method, used to investigate the effects of tortuosity, wedge angle, diameter of proppant, fluid velocity on the migration and placement of proppants. The results reveal that the migration and distribution of proppant in tortuous-wedge fractures exhibit significant disparities when compared with straight fractures or tortuous fractures. Proppant migration in tortuous-wedge fractures is divided into the suspended sand stage, sand bed rapid growth stage and top suspended sand stage according to the main force. The proppant transport distance increases with the increase of the wedge angle. Compared with the tortuous fractures with a wedge angle of 0°, the migration distance of proppant in the tortuous wedge fractures, t = 1 s, wedge angles of 1° and 2° increased by 16% and 29%. However, with the increase of it, the congestion of the proppant may also occur, and there is a critical angle. The greater the tortuosity, the greater the kinetic energy loss of particles and the advancing angle of the dune. Compared with the straight fracture, t=3 s, and the average velocity is reduced by 36%, and 45%. In addition, the proppant migration in tortuous-wedge fractures is non-uniform distribution, and the dune is higher in the tortuous place. This study benefits to understand the migration mechanism of proppant in fractures. It can provide theoretical guidance for the stimulation of unconventional reservoirs.

1. INTRODUCTION
Hydraulic fracturing is an important means of reservoir stimulation and improving oil and gas recovery. By pumping high - pressure fluid, the reservoir is broken and proppant particles are injected to fill the fractures, forming a long - term high conductivity channel for oil and gas in the reservoir. Proppant migration in fractures is a fluid - solid coupling problem among reservoir fluid, proppant particles and fracture walls. The migration and distribution of proppant depend on the physical parameters of particles, fluids and fractures, the distribution of flow field and pressure field in complex fractures, and the mechanism of action is complex. Scholars have carried out a lot of research based on indoor physical experiments and numerical simulation methods.
Stress Corrosion Cracking in Carbonates Initiated by Carbonic Acid, A Reactive Molecular Dynamic Simulation
Authors: Wang Jingru , Liu Yuetian , He Yuting , Liu Xinju , Lin Ziyu , Zhang Bowei , Chai Rukuan 
Published: August 2024

ABSTRACT:
As the greenhouse effect gradually intensifies, addressing CO2 as the primary greenhouse gas has become a pressing concern. Currently, the predominant carbon sequestration technique involves storing CO2 in reservoirs or saline aquifers. However, CO2 readily dissolves in water, forming carbonic acid, which can compromise geological formations and lead to stress corrosion cracking. Stress corrosion cracking (SCC), a chemical activation mechanism, involves fluid adsorption on crack surfaces and fluid-assisted crack propagation. While there is extensive research on the stress corrosion cracking of CO2 in quartz crystals, investigations on stress corrosion cracking in gas-water-carbonate rock systems remain limited. Moreover, the carbonic acid formed when CO2 dissolves in water can engage in complex chemical reactions with carbonate rocks, exacerbating the corrosion and cracking of carbonate rocks. This study focuses on carbonate reservoirs, representing them using calcite crystals. Molecular dynamics simulation is employed to investigate stress corrosion cracking in pre-cracked calcite crystals under fluid interaction. By comparing the cracking behavior of calcite crystals in different environments, the intrinsic mechanisms of crack propagation are analyzed. This study indicates that carbonate fluids have a strong impact on the subcritical expansion of cracks. During the stress corrosion cracking process, Ca-O bonds are the first to break. H atoms from the external environment readily form H-O bonds and C-H bonds on the surface of calcite, with H-O bonds binding to Ca atoms, accelerating the fracture of Ca-O bonds. In a carbonate environment, H atoms infiltrate the interior of calcite more rapidly, binding with C and O atoms, creating crystal vacancies, and intensifying the extent of stress corrosion cracking. This study aims to explore the damage to carbonate rock reservoirs during the CO2 storage process and analyze the gas-water-rock interactions in enhanced oil recovery with CO2 injection or during CO2 fracturing processes. These findings contribute to describing the details of rock fracturing and provide insights for the development of effective oil and gas extraction and carbon sequestration technologies.
Simulating Large-Scale Supported Pillar Laboratory Experiments in 3DEC
Authors: Chaurasia A. , Walton G. 
Published: August 2024

ABSTRACT:
Underground mine pillars are typically supported using rockbolts, wire mesh, shotcrete liners, or a combination of these methods to enhance stability and maintain their load-bearing capacity. The design of these supports is generally based on field experience, which is often site-specific, making them less applicable to all geological and loading conditions. Advancements in computational power have made it feasible to utilize numerical tools to simulate and analyze complex deformation behavior effectively. Discrete Element Methods (DEM) are more suitable than continuum modeling tools for simulating large displacements and accounting for the influence of rock support. This study employed a bonded block modeling approach in 3DEC to simulate pillar deformation and support behavior under monotonic loading conditions for three different width-to-height ratios (0.5, 1, and 2). These models were calibrated against large-scale laboratory compression test data for a porous limestone with a cross-section of 0.5 × 0.5 m2. The objective was to evaluate the ability of a model calibrated against unsupported pillar test results to reproduce observed ground-support interaction trends for supported pillar tests. The supports, such as grouted rock bolts, face plates, and wire mesh, were explicitly represented using built-in structural elements to resemble the laboratory tests, and their properties were calibrated using a trial-and-error approach until the simulation reasonably matched the laboratory results. The effects of the support systems on the peak strength, residual strength, and deformational behavior of the pillar were evaluated for all three width-to-height ratios.

1. INTRODUCTION
Underground mine pillars play a crucial role in providing natural stability to the roof and ensuring safe working conditions for both workers and machinery. Despite engineering design efforts, the challenges of ground falls and pillar failures persist and continue to be concerns in the field. Consequently, support systems such as rockbolts, wire mesh, face plates, and shotcrete are frequently employed to stabilize pillars, limiting the progression of spalling and pillar degradation, and mitigating the associated risks of sudden or violent pillar failure (Kaiser et al., 1996; Mohamed et al., 2016). Therefore, pillar design should consider rock-support interaction in addition to common geological and loading considerations.
Cyclic Loading-Unloading Impacts on Salt Cavern Stability: Implication for Underground Hydrogen Storage
Authors: Chang Kyung Won , Ross Tonya S. A. 
Published: August 2024

ABSTRACT:
Underground caverns in salt formations are promising geologic features to store hydrogen (H2) because of salt's extremely low permeability and self-healing behavior. Successful salt-cavern H2 storage schemes must maximize the efficiency of cyclic injection-production while minimizing H2 loss through adjacent damaged salt. The salt cavern storage community, however, has not fully understood the geomechanical behaviors of salt rocks driven by quick operation cycles of H2 injection-production, which may significantly impact the cost-effective storage-recovery performance. Our field-scale generic model captures the impact of combined drag and back stressing on the salt creep behavior corresponding to cycles of compression and extension, which may lead to substantial loss of cavern volumes over time and diminish the cavern performance for H2 storage. Our preliminary findings address that it is essential to develop a new salt constitutive model based on geomechanical tests of site-specific salt rock to probe the cyclic behaviors of salt both beneath and above the dilatancy boundary, including reverse (inverse transient) creep, the Bauschinger effect and fatigue.

1. INTRODUCTION
Hydrogen (H2) is an attractive energy storage medium due to its high specific energy and clean performance [U.S. DOE Regional Clean Hydrogen Hubs Program (H2Hubs)]. However, the low density of H2 requires large-scale, high-pressure endurable storage sufficient to meet the scalable supply and demand. Underground caverns in salt formations can be suitable storage reservoirs due to low permeability and self-healing behaviors of the salt rock. In the United States, domal salts located in the Texas Gulf Coast region are potential targets to store H2 because off their storage volumes, as well as their proximity to critical markets and infrastructure.
Successful salt-cavern H2 storage schemes must maximize the efficiency of cyclic injection-production operation while minimizing H2 loss through adjacent damaged salt. Underground H2 operation can result in three major geomechanical behaviors: (1) cavern volume changes with creep (creep rate will vary depending on operation cycles), (2) potential leakage through damaged caprock nearby the wellbore, and (3) hydraulic and mechanical interactions among multiple caverns, including presence of fractures, stress transfer etc. (Figure 1). However, the salt cavern storage community has not studied these geomechanical behaviors of salt rocks driven by quick operation cycles, which may have a significant impact on the cost-effective storage-recovery performance.
Experimental and Numerical Validation of Cooling-Induced Stress Change Within a Caprock Shale – Seal Integrity Insights from the Northern Lights CCS Project
Authors: Thompson N. , Griffiths L. , Bjørnarå T. I. , Smith H. , Andrews J. S. 
Published: August 2024

ABSTRACT:
As Carbon Capture and Storage (CCS) is experiencing rapid growth, there is increased focus on the geomechanical integrity of the storage system(s). In addition to pressure limitations, thermal influences (due to injection of cold CO2 into a warmer subsurface) can play an important role in defining the geomechanical integrity of the caprock seal. Through analytical investigation, Thompson et al. (2021) recognized that undrained pore pressure effects in low permeability caprocks alter the effective stress picture of the caprock, as the caprock may be cooled significantly due to conduction processes. This paper builds on that work and presents laboratory data from specially designed thermal uniaxial strain testing in caprock shale material, as a validation exercise for the analytical investigation. The results of these tests are directly compared to confirm the analytical approach and to determine lab-calibrated parameters that can be used for further simulation and assessment of caprock integrity. Where the experimental and analytical approaches serve as end member descriptions of the effective stress evolutions (drained versus undrained) from cooling, numerical simulations are also performed to quantify additional factors that may affect the effective stress response. All three approaches are found to be consistent, qualifying the analytical approach as a robust means of thermal influence investigation for caprock integrity evaluation.

1. INTRODUCTION
In the challenge to meet net zero ambitions, the Carbon Capture and Storage (CCS) industry is developing rapidly, with a high number of large-scale projects planned and/or coming on stream in the coming years (Global CCS Institute [2023]). Integrity assurance of the subsurface storage systems is paramount and, subsequently, geomechanical characterization and risk assessment is recognized as first-order contribution to storage site feasibility and storage volume potential (Rutqvist [2012]).
Inherent to CO2 injection and storage are changes in pore pressure that need be assessed in terms of geomechanical integrity. Thermal changes can also be equally as important, as the injected CO2 is often significantly colder than the temperature of the storage formations. Such thermal influences may result in significant changes in effective stress both in the reservoir/storage and caprock/seal formations and therefore must be fully assessed in order to fully quantify the geomechanical risk for a given storage project.
Laboratory Procedure to Calibrate Non-Stressed Borehole Size
Authors: Lin C. , Zou D. H. S. 
Published: August 2024

ABSTRACT:
Measurement of the pre-excavation 3D stresses is of great importance for mining, petroleum and other underground rock engineering. An alternative method by differential-direction drilling (called D3 method) without overcoring was recently developed based on back-analysis of the measured borehole diametrical deformation. One of the key input parameters in this back-analysis method is the borehole convergence. To calculate the convergence, the initially-drilled borehole diameter before deformation is required. The rock mass in the ground is always under stress and a drilled hole size is the ultimate result after deformation. Additionally, the size of a borehole typically deviates slightly from the nominal drill bit size. Hence, the first step is to determine the actual borehole size under zero stress to provide a base for comparison in practical implementation. This paper presents the laboratory experiment setup and the procedure for drilling and measurements. Boreholes are drilled in non-stressed rock blocks using a drill press and customized drill bits. The borehole size is measured with a borehole deformation gauge and calibrated with a precisely machined aluminum tube. The relationship between the borehole size and the nominal core bit size is thus established. A calibration procedure for determining the non-stressed borehole size is ultimately established through laboratory experiments.

1. INTRODUCTION
Pre-excavation stresses refer to the stresses existing within a rock mass before the initiation of any excavation or mining activity. It influences the stability of underground structures and excavations (Hoek and Brown, 1980; Amadei and Stephansson, 1997; Brady and Brown, 2004). Incorporating the pre-excavation stress analysis into engineering practices in mining, petroleum, and underground rock engineering is essential for ensuring safety, optimizing design, maximizing resource recovery, and managing risks, ultimately contributing to the sustainable development of these industries.
The pre-existing field stresses are in three dimensions, which can be described by six independent components. It can also be represented by three orthogonal principal stresses: the maximum, the intermediate and the minimum normal stresses (Zou, 2020). Unlike one-dimensional or two-dimensional stress analyses in different directions, which oversimplifies the stress distribution, stress analysis in three dimensions provides a more comprehensive understanding of how stresses act within the rock mass. This understanding is crucial for accurate engineering design and risk assessment.
Numerical Simulation of Flow Field and Erosion Characteristics in Hydraulic Fracturing Tool
Authors: Song Xianzhi , Cui Yueqi , Zhou Mengmeng , Zhengming Xu , Zhu Zhaopeng , Li Gensheng 
Published: August 2024

ABSTRACT:
Hydraulic fracturing is widely used in oil and gas reservoir production enhancement due to its notable attributes: more convenience, high efficiency, simple tool structure, absence of mechanical sealing, no compaction zone, and the ability to precisely create directional seams. During the hydraulic fracturing process nozzle dislodgement, tool leakage, and other tool failure phenomena are common occurrences, which result in the waste of time and cost and threaten the safety of the construction. Therefore, this paper uses the Computational Fluid Dynamics (CFD) method coupled with the Discrete Phase Model (DPM) to study the flow field inside the tools to get the erosion law near the nozzles of common hydraulic fracturing tools. The model has verified the accuracy by comparing it with the failed tool salvaged from the oil field. The simulation results show that the erosion phenomenon is concentrated at the top of the upper nozzle and the bottom of the lower nozzle. Meanwhile, a new erosion graphical plate is established, based on the effects of flow rate on erosion, to help and guide the modification and upgrading of hydraulic fracturing tools and the prediction of tool life.

1. INTRODUCTION
Oil and gas resources are traditional non-renewable energy sources, and how to carry out reservoir transformation to improve the production of the oilfields has become the top priority for the development of the old oilfields in the future (Zou et al., 2016). Hydraulic jet fracturing technology can improve the seepage conditions of reservoir and achieve the purpose of increasing production, which is recognized as an efficient horizontal well completion technology (Huang et al., 2017,Li and Wu,2022). During the operation, a large number of high-velocity particles continuously wash and erode the wall surface of the fracturing tools, resulting in large erosion and wear, which may lead to tool failure in serious cases and affect construction safety (Tang et al., 2015). At the same time, according to the photos of the tools taken at the field-site, it is not difficult to find that the erosion problem of hydraulic fracturing tools is very serious, especially in the area near the nozzle inlet, and the nozzle often falls off and leads to tool failure, which not only affects the progress of the operation, but also results in a waste ofcosts. Erosion is commonly found on the internal and external surfaces of tools, the impact factors of erosion are numerous and the mechanism is complex.
Mechanical and Hydraulic Characterization of 3D Printed Rock Analogues of Poorly Cemented Sandstone
Authors: Cartagena-Pérez D. , Rangriz Shokri A. , Zambrano Narvaez G. , Chalaturnyk R. 
Published: August 2024

ABSTRACT:
This study presents a mechanical characterization of multiple 3D printed rock samples with silica sand grains that were aimed to emulate the behavior of poorly cemented sandstones. The printing process consisted of spraying a liquid binder onto a bed of sand grains, layer by layer, followed by a curing process. To assess the quality of cementation through binder distribution, we employed Computed Tomography (CT) to get high-resolution images of the printed rock specimen. Subsequently, we conducted porosity measurements using both water and canola oil. To complete the work, intact samples at low binder saturation (i.e. cementation) underwent several UCS and triaxial tests, along with permeability measurements.
Our results indicated an average porosity of 46% for poorly consolidated 3D printed rock analogues. The average UCS was 1.45 MPa, with a Young's modulus of 175.18 MPa; our experimental data from 3D printed rock samples align closely with actual core measurements of poorly cemented sandstones, as reported in literature for locations such as Cold Lake and McMurray heavy oil reservoirs. Following UCS testing, we observed diagonal shearing failure planes in all samples. Triaxial testing indicated low cohesion (350 kPa) and frictional angle akin to dense sands (56°), leading to a loose sand structure upon shearing. Regarding their hydraulic properties, we also conducted permeability tests at an effective confining stress of 0.5 MPa which revealed an average permeability of 1.8 Darcies, again consistent with poorly cemented sandstones.

1. INTRODUCTION
Implementation of engineering solutions in geomaterials often necessitates a comprehensive hydromechanical characterization, which involves destructive tests using multiple samples, such as uniaxial compressive strength (UCS) and triaxial tests. In response to this demand, additive manufacturing (i.e. 3D printing) technology has emerged as a cost-effective means of obtaining a substantial number of identical rock samples. This capability allows researchers and engineers to carry out multiple tests (Including destructive ones – e.g. triaxial tests) without the limitation in number and price of samples that come from actual reservoirs. This advantage is useful if the 3D printed rock is partially representative of the rocks in the reservoirs.