bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study of Proppant Crushing and Conductivity Reduction Within Rough Fracture in Shale Gas Formations
Authors: Liu L. , Ma X. F. , Zou Y. S. , Zhang S. C. , Zhang X. H. , Wang W. C. , Liu S. K.
Published: August 2024

To investigate the impact of surface roughness on proppant crushing and its effect on fracture conductivity in Shale Gas Formations, laboratory conductivity experiments were performed on standard core columns drilled along hydraulic fractures. The morphology of proppants within the fractures was observed using computed tomography (CT) and scanning electron microscopy (SEM). The results indicate that the roughness of the fracture surface has a greater impact on ceramic proppants than on quartz sand in terms of crushing rate. For high roughness surfaces, quartz sand is suitable for shallow reservoirs, while ceramic proppant is more suitable for deep reservoirs. The rougher the surface of the fracture, the greater the decrease in its conductivity. When the compressive stresses vary from 20 MPa to 50 MPa, the quartz sand crushing rate increases from 10% to 33%, while the ceramic proppant crushing rate grows from 8% to 22%. The CT scan results indicate that the proppant is prone to breakage at the raised area of the fracture surface. The scanning electron microscopy (SEM) results show that the proppant is more prone to crushing and damage at the raised areas of the surface of the fracture. This article innovatively analyzes the crushing of proppants under various rough fracture surfaces, offering guidance for optimizing proppants in different reservoir conditions.

1. INTRODUCTION

On a global scale, oil and gas resources remain irreplaceable and non-renewable energy sources. With the decreasing recoverable reserves of conventional oil and gas resources year by year, shale oil, as a new type of unconventional oil and gas resource with great potential, has become an important component of global oil and gas resources (Shah et al., 2010; Davies et al., 2012; Zeng and Wei, 2017). Reservoir fracturing transformation is the core technology for enhancing the utilization of oil and gas reservoirs (Cui A et al., 2014; Saldungaray PM et al., 2015). However, the effective establishment of an artificial fracture network in reservoir fracturing transformation is crucial for creating high-conductivity oil and gas flow channels. The efficient migration and placement of proppants in artificial fractures are fundamental for enhancing the support provided by fractures. (Asabi et al., 2018; Wei et al., 2019; Ghanizadeh et al., 2016; Han, J. A. et al., 2016).
A Study of the Key Factors Associated with a Massive Pillar Failure in an Underground Limestone Mine Using Numerical Models
Authors: Rashed G. , Yuting X. , Evanek N.
Published: August 2024

Several massive ground collapses occurred in the past decade in US underground stone mines where surface subsidence occurred in most of them. The occurrence of a massive ground collapse in stone mines places the mine workers at great risk. The National Institute for Occupational Safety and Health (NIOSH) initiated a project to better understand the causes of these massive collapses and reduce/eliminate their future occurrence. Previously the authors investigated one of these massive collapses and it was found that pillar failure was the most likely cause for the collapse. In this study, the authors further investigated the impact of pillar benching, karst cavities, and geological discontinuities on the potential for pillar failure. 3D LiDAR scans were utilized to determine the extent, location, and dimensions of the karst cavities. Stress and deformation analysis were conducted using 3DEC models to gain more insight about the impact of floor benching and poor rock mass quality on stone pillar stability. Poor rock mass quality can be attributed to the existence of karst cavities, small joint spacing, and poor joint conditions at the study mine. Based on the numerical modeling results, floor benching in association with linear karst cavity and geological discontinuities in pillars can create a large uncontrolled displacement, sliding along pre-existing joints, and induce tensile stresses near the center of the pillar that may result in a brittle pillar failure.

INTRODUCTION

Between 2015 and 2021, five massive ground collapses occurred in underground room-and-pillar stone mines in the United States (Evanek et al., 2022 and Rumbaugh et al., 2022). The depth of cover at these collapses was less than 600 ft (∼183 m). These events pose a significant risk of ground failure and air blast that may result in injuries, fatalities, destruction of ventilation controls, and a potential surface subsidence (Evanek et al., 2022). In general, massive collapses can be attributed to roof or pillar failure. An example of massive roof failure is the collapse that occurred at the Lake Lynn Experimental Mine (Iannacchione et al. 2007), while the collapse that occurred at Whitney mine was an example of pillar failure (Esterhuizen et al., 2018).
Assessing CO2 Leakage Risks and Fault Stability: A Coupled Flow and Geomechanics Simulation with Uncertainty Analysis of Fault Properties
Authors: Yoon Sangcheol , Prioul Romain , Bailey William J. , Birchwood Richard , Rodriguez-Herrera Adrian , Stefani Joe
Published: August 2024

This study investigates coupled flow and geomechanics simulations of carbon dioxide (CO2) injection within a hypothetical saline aquifer. We intentionally set a scenario to enable fluid migration and fault reactivation in the synthetic model of the SEG Advanced Modeling Corporation (SEAM) CO2 project. The numerical model consists of a main turbidite aquifer, along with several geological layers including a capping shale layer, middle, as well as upper aquifers. In addition, two faults, western and eastern, cut across the section striking North-South. We assume the western fault is a sealing fault while the eastern side has either no fault or is an open fault with a high-permeability damage zone. Our modeling approach employs fine grids near the faults to explicitly represent the fault's 6-m thin damaged zone. We also use a Mohr-Coulomb failure envelope for nonlinear plastic analysis into a two-way coupling scheme. We undertook a stochastic analysis to quantify the impact of fault properties on their post-failure behavior. Using the stress path along the fault plane over time, we show that the characteristics of faults can significantly affect areas of reactivation. Assuming uniform fault properties, an increase in pore pressure can cause shear failure at the upper or lower parts of the fault where it intersects with the target aquifer, because of a significant increase in shear stress. Sensitivity analysis of various parameters, suggests a time evolution of the fault response, with an early emphasis on parameters like cohesion and friction angle affecting reactivation timing. Over time, the permeability of the damage zone gains prominence, influencing the extent of fault reactivation due to its effect on the pressure propagation of the damage zone. Coupled flow and geomechanics simulation can provide useful insights into establishing robust measurement and monitoring plans to mitigate fault reactivation and fluid migration through faults. While the choice of the Mohr-Coulomb model was consistent with our scenario-based approach to "magnify" the effects of fluid migration for this study, we note that in real field situations, other fit-for-purpose plasticity models with different fault permeability evolution may be more appropriate.
Geomechanical Properties of Hydrate-Bearing Sediments from the Gulf of Mexico - Viscoplastic Behavior
Authors: Cardona Alejandro , Bhandari Athma R. , Flemings Peter B.
Published: August 2024

The geomechanical behavior of hydrate-bearing sandy silts controls in-situ stresses and compression upon hydrate dissociation. Here, we measure the uniaxial strain compression of natural hydrate-bearing (pressure cores) and hydrate-free reconstituted samples from Green Canyon 955 - deepwater Gulf of Mexico. We document these hydrate-bearing sandy silts behave viscoplastically. Under constant strain rate compression under uniaxial strain conditions, sandy-silts with hydrate are stiffer but have a larger uniaxial lateral stress ratio (K0) than equivalent non-hydrate-bearing sediments. When we pause the compression, the stress ratio increases towards K0 = 1.0 in the hydrate sample, whereas the K0 remains constant for the hydrate-free sample. We develop a model to link these experimental observations quantitatively. Our model assumes that the hydrate phase and the sediment skeleton share any applied external load. Model results show the hydrate phase bears a more significant fraction of the applied load because the hydrate is less compressible than the sediment skeleton. The viscoplastic behavior of hydrate-bearing sediments will impact gas production and in situ stresses. For example, viscous deformation away from the production zone affects water flow, affecting gas and water flow rates closer to the well. Furthermore, the time dependency of the stress ratio may affect hydraulic fracturing strategies in these reservoirs as the rate of pressurization may impact stress evolution on the wellbore.

1. INTRODUCTION

Gas hydrates are crystalline solids with guest molecules trapped within water lattices (Sloan and Koh 2007). In natural environments, methane is the most common guest molecule. These compounds are stable at high pressure and low temperature, which delimits their geological distribution to permafrost and submarine settings (Boswell and Collett 2011). Methane hydrates are envisioned as a new energy resource and an active component in the carbon cycle.

Silt- and sand-rich marine environments commonly host high concentrations of hydrates. Coarse-grained deposits in Green Canyon 955 (GC 955) - Gulf of Mexico (Flemings et al. 2020; Meazell et al. 2020), Krishna-Godavari Basin offshore India (Collett et al. 2019), and in the eastern Nankai Trough in offshore Japan (Komatsu et al. 2015) contain hydrate saturations exceeding 80%.
Elastic Wave Behaviors Across Rocks Subjected to Cyclic Tensile Loads
Authors: Yang Hui , Han Dongya , Wu Shan , Zhao Qi
Published: August 2024

Understanding wave behaviors across rocks exposed to cyclic loads is of great significance to the communities of geomechanics and geophysics. This study aims to investigate the elastic wave properties of rocks (including wave speed, amplitude, and dominant frequency) under the cyclic tensile loading condition. For this purpose, we performed ultrasonic measurements on quartz diorite rock sample during the progressive cyclic direct tensile loading (PCDTL) experiments via a custom-built test system. Our results indicate that wave responses of the quartz diorite rock under the PCDTL condition are highly affected by the applied cyclic tension. Specifically, increasing tensile load causes reductions in wave velocity, amplitude, and dominant frequency during the uploading process of each cycle, and the recovery of these wave properties is observed during the corresponding unloading process. The recovery of wave signatures gets lower with the increasing cyclic number, indicating that the cumulative tension cycles cause accumulated drops in wave attributes. Besides, wave amplitudes exhibit more significant changes compared to wave velocity and dominant frequency during the PCDTL procedure. The findings of this research provide insights into the cyclic tension-induced evolution of wave properties in rock masses and may serve as guidance for the interpretation of field-scale geophysical data.

1. INTRODUCTION

Rock masses are frequently subjected to cyclic loads stemming from geological processes (like tectonic movements), rock engineering applications (e.g., drilling and blasting), seismic activities (such as earthquake rupturing and volcanic eruption), etc. (Bagde et al., 2005; Haimson, 1978; Xiao et al., 2010). Therefore, characterizing the properties of rocks under cyclic loading conditions is of great significance to underground tunneling and excavation, the extraction of hydrocarbon resources and geothermal energy, the evaluation and maintenance of rock structures, and so on (Cerfontaine and Collin, 2018). Since elastic waves are an effective and efficient tool for monitoring and characterizing subsurface rocks, understanding elastic wave behaviors in rocks under various stress states has been one of the hotspots in geophysics and geotechnics (Barton, 2006; Winkler et al., 1979).
Is there a Universal Rock Mass Classification System?
Authors: Ambah E. , Elmo D.
Published: August 2024

This paper examines the consequences of subjectivity on universal design methodologies, and emphasizes the need for a cohesive and globally accepted rock mass classification (RMC) framework to foster innovation and efficiency in rock engineering projects. Challenges posed by varied rock mass classification systems and core logging practices complicate the task of data collection and preparation for emerging technologies. Integrating new technologies into rock engineering relies heavily on quality, standardized data. Inconsistencies in terminology, measurement standards, and emphasis on specific rock characteristics can introduce biases which will hinder the development of robust designs. This paper examines the importance of overcoming data preparation hurdles in order to utilize the full potential of new technologies in rock engineering. By unravelling the intricacies of this multidimensional problem, this study provides a foundation for discussions on standardization, collaboration, and innovation within the field, ultimately paving the way for more reliable and efficient rock engineering practices on a global scale. This research aims to provide insights that will contribute to the overarching goal of developing universal design methods for rock engineering while addressing the current challenges of data preparation in rock engineering.

1. INTRODUCTION

In the past few years, the field of Artificial Intelligence has flourished. Numerous, unrelated industries have adopted machine learning to improve workflow, worker safety and productivity (Patel et al., 2021). Interest in artificial intelligence models for applications in the Rock Engineering field has increased significantly in recent years.

Artificial Intelligence (A.I.) was defined by John McCarthy (2004) as "the science and engineering of making intelligent machines, especially intelligent computer programs. It is related to the similar task of using computers to understand human intelligence, but AI does not have to confine itself to methods that are biologically observable". To this end, various models have been developed and deployed for Rock Engineering applications such as using Convoluted Neural Networks (C.N.N.) for optical rock fracture mapping (Azhari et al, 2021).
Longwall-Induced Shale Gas Well Casing Deformations and Stresses-Critical Effects of Geologic and Geometric Parameters
Authors: Su W. H. , Zhang P.
Published: August 2024

This paper summarizes geo-mechanical findings from the ongoing Gas Well Stability research at the National Institute for Occupational Safety and Health (NIOSH)-in particular, the critical effects of geologic and geometric parameters on longwall-induced gas well casing deformations and stresses. Overburden geology is one of the most important factors affecting the longwall-induced casing deformations and stresses. The large contrast of bending stiffness at the soft-to-hard rock interfaces has been found to induce large casing deformations and stresses. Overburden depth to the mining seam is also an influential factor. Shallow overburden depth induces large horizontal displacement and resulting casing deformation and stress, due to smaller longwall-induced vertical pressure. Deep overburden depth induces large longwall-induced vertical pressure, which tends to limit longwall-induced horizontal movement. Strata dip would magnify longwall-induced deformations by 20% for each degree of strata dip with down dip longwall excavation. The gas well setback distance is a critical geometric parameter. The effect of longwall-induced deformation decreases exponentially as the setback distance increases. Longwall-induced casing deformation and stress will be mitigated or totally uncoupled if the production casing is uncemented. Longwall-induced fracture zone height is linearly propositional to the panel width.

1.I NTRODUCTION

Over 2,000 unconventional shale gas wells have been drilled through active and future Pittsburgh Seam coal reserves in Pennsylvania, West Virginia, and Ohio. These unconventional gas wells, whether tapped into the Marcellus or Utica formations, contain very high gas pressure and volume. Strata deformations associated with underground longwall coal mining could induce stresses and deformations in the shale gas well casings, which in certain situations could compromise the mechanical integrity of the production casing. Damaged production casing could potentially introduce high-pressure, high-volume explosive gas into underground mine workings to jeopardize underground miners' safety and health.

To provide critical scientific data to the stakeholders, which includes the Mine Safety and Health Administration, Pennsylvania Department of Environmental Protection, West Virginia Department of Mine Safety and Training, Ohio Department of Natural Resources, coal operators, and gas operators, NIOSH initiated a gas well stability research program in 2016 to evaluate the effects of longwall-induced deformations on shale gas well casing integrity under deep, medium, and shallow covers. This paper summaries important findings from the ongoing NIOSH Gas Well Stability research; in particular, the important geo-mechanical research findings on overburden geology, overburden depth, strata dip, gas well setback distance, gas well casing cementing alternative, and longwall-induced fracture zone.
Assessment of Subsurface Ice-Based Thermal Energy Storage: THM Coupled Geomechanical Study
Authors: Tounsi H. , Zhang Y. , Rutqvist J. , Birkhozler J.
Published: August 2024

Ice-based thermal energy storage systems, utilizing both sensible and latent heat capacities of water, have achieved successful commercialization and are currently operational in numerous installations worldwide. However, conventional chilled water and ice-based energy storage systems often necessitate substantial space to store significant quantities of cooling energy. To address this limitation, the subsurface emerges as a promising solution. Nevertheless, the freezing of the ground introduces potential alterations in its behavior, leading to changes in pore pressure and ground movement.

In this study, the TOUGH multiphase flow code was enhanced by incorporating water/ice phase change capabilities and subsequently validated against analytical and experimental data. Our investigation focused on the subsurface as a potential storage site for ice, taking into account the impact of ground permeability, spacing between freezing pipes, freeze/thaw damage, and refrigerant temperature. Numerical simulations using a Thermo-Hydro-Mechanical approach were conducted over a 10-year period, representing 10 cycles of seasonal freeze/thaw, to comprehensively assess the performance and long-term stability of a generic subsurface ice storage system.

1 INTRODUCTION

Amid the global push for sustainable energy solutions, the reliability of renewable sources like solar and wind power is undeniable. However, their intermittent nature highlights the urgent need for efficient energy storage to balance clean energy supply and demand. This paper focuses on addressing the demand for cooling in hot regions, driven by rising temperatures due to climate change. Among various energy storage technologies, ice thermal storage has shown promise for building cooling at a district scale (Chan et al., 2006; Gang et al., 2016). This method typically involves chilling a glycol solution, circulating it through coils immersed in a water tank to freeze the water during off-peak hours, and then thawing the ice for cooling during peak hours.

Despite the proven effectiveness of ice thermal storage, challenges arise when integrating renewable energy sources into the freezing process, particularly in urban areas due to space constraints (Yan et al., 2016). To address these challenges, this study explores the concept of subsurface ice-based thermal energy storage. This innovative approach involves installing underground freeze pipes through which a glycol solution circulates, allowing the ground to freeze in winter and extracting the stored cold energy for air conditioning in summer.
Effect of Thermal Cycling on Cemented Sandstone in Relation to CCS
Authors: Smith H. , Soldal M. , Grande L. , Griffiths L.
Published: August 2024

As widespread Carbon Capture and Sequestration becomes more relevant, challenges related to thermal cooling upon injection and the potential for significant stress perturbation needs to be accounted for in geomechanical modelling. The current work shows an example of how temperature fluctuations related to CO2 injection can affect the stress changes within a reservoir using a stiff cemented sandstone analogue for deep reservoirs, and further demonstrates how a laboratory test program can be efficiently used to better define thermal aspects of typical geomechanical parameters such as Young's moduli and Poisson's ratio. The current program has shown how elastic moduli can be affected by changes in temperature, and how these changes can affect the estimation of stress changes within a reservoir. This comprehensive triaxial test also displayed a non-linear behavior at lower effective radial stresses during temperature reduction, which can be related to plastic deformation achieved during cooling.

1. INTRODUCTION

As carbon capture and Sequestration (CCS) has gained the public's attention, the necessity to demonstrate that CCS can be deployed safely is key to make CCS an accepted solution as a contribution for reducing global emissions. To predict the reservoir response and ensure safe operations, geomechanical models are used to determine the influence of pressure and temperature change due to injection on the in situ stress conditions.

To provide accurate predictions, one of the first steps will be the production of relevant laboratory data to both populate numerical models with the relevant parameters, and to validate these models through laboratory experiments simulating pressure and temperature changes expected due to injection.

These models will need to accommodate reservoir responses to typical challenges related to CCS. Thermal effects play a significant role in the geomechanical behavior of reservoirs during CCS operations, where cool CO2 is injected into a warmer reservoir. The resulting changes in temperature lead to contraction of the rock matrix and modification of the stress state (Fjær, 2008; Søreide et al., 2014; Thompson et al., 2021). In sandstone reservoirs, cooling is expected to lead to reduction of effective horizontal stress due to thermal contraction of the rock (Søreide et al., 2014). This reduction in horizontal stress can potentially lead to a more critical stress-state. To understand and predict the influence of temperature on stress in the reservoir, it is critical to determine the relative parameters that may be used to model the influence of cooling.
Design of a Meso-Scale Test of a Fracture Thermal Energy Storage (FTES) System
Authors: Burghardt J. , Lecampion B. , Möri A. , Linneman D.
Published: August 2024

Seasonal storage of thermal energy has the potential to both significantly reduce the total energy requirements for heating and cooling of buildings, and also allow for the flexibility to store thermal energy from intermittent sources. With approximately half of global energy consumption currently being used for heating and cooling, this represents an important path to reducing greenhouse gas (GHG) emissions. The concept of FTES is to drill two or more wells into a low permeability formation and then generate hydraulic fractures to create flow paths for water to circulate between the wells. Hot or cold thermal energy can then be stored in the surrounding rock mass by circulating hot or cold water through the fractures, which will heat or cool the rock mass. To recover the stored energy, ambient temperature water can be then circulated through the fractures, which will then be heated or cooled by the rock mass. Fractures inherently have a very large ratio of surface area to volume. This allows for very high heat fluxes to and from the rock mass to be achieved despite the relatively low thermal conductivity of most geologic formations. Because large fractures can be made with low-cost equipment and with only inexpensive and environmentally safe materials such as water and sand, the cost to construct even large FTES systems is expected to be quite low. A preliminary estimate is made for the size and operating conditions of a full-scale FTES system capable of heating a commercial building. The paper then presents a dimensional analysis of this system. The scaling parameters that come from this analysis are then used to design an intermediate-scale field test of a fracture thermal energy storage system (FTES) to be conducted at the Sanford Underground Research Facility (SURF) in Lead, SD.

1 INTRODUCTION

Approximately half of global energy consumption is used for heating and cooling. Because fossil fuels are used to meet most of this demand, heating and cooling of buildings produces a large portion of global greenhouse gas (GHG) emissions. Seasonal storage of thermal energy is a powerful technology to substantially reduce the energy required for heating and cooling of buildings and to reduce or eliminate the associated GHG emissions. This paper focuses on an emerging technology for seasonal thermal energy called fracture thermal energy storage (FTES). FTES is a technique for building a highly efficient heat exchanger by creating a carefully designed set of fractures in the ground below a building.
Semi-Automated Geotechnical Workflow Utilizing UAV Data for Enhanced Hazard Assessment and Safety at Rio Tinto Kennecott
Authors: Fahle L. , Bakken K. M. , Telfer J. , Williams C.
Published: August 2024

Spending time near highwalls, e.g., while performing geotechnical cell mapping, is a critical risk. Rio Tinto Kennecott (RTKC) is actively seeking out solutions to minimize this risk. To this end, RTKC employs Uncrewed Aerial Vehicles (UAVs) for 3D-model-based structural mapping. We developed a prototype of a semi-automated workflow to better utilize UAV data and enhance personnel safety near highwalls. Our workflow includes three main components: a GIS-enabled dashboard to locate relevant UAV data, semi-automated bench-scale kinematic analysis and risk evaluation, and another GIS-enabled dashboard to share results. We show that our workflow allows for efficient geotechnical data collection, enables a high-level pit-wide kinematic risk assessment, and provides data for risk communication and further analysis. Our proposed system has the potential to further enhance RTKC's geotechnical hazard assessment processes and therefore improve safety around highwalls.

INTRODUCTION

1.1. Background and Context

Safety around highwalls in mining is crucial due to the potential hazards they pose. Geotechnical hazards are one of the major risks associated with highwalls. Highwalls can collapse without warning, leading to severe injuries, loss of life, and destruction of equipment.

The Mine Safety and Health Administration (MSHA) has issued safety alerts and guidelines emphasizing the importance of conducting highwall examinations, assuring hazards are addressed, and developing plans for highwall controls to prevent accidents and fatalities (Mining Safety and Health Administration, 2024). Research projects, such as those conducted by the National Institute for Occupational Safety and Health (NIOSH), focus on addressing rockfall hazards and developing slope monitoring techniques to improve highwall safety in open pit mining (Centers for Disease Control and Prevention, 2020).

Despite these risks, access to mining highwalls is required for various tasks including installation and maintenance of infrastructure such as dewatering wells or geotechnical monitoring equipment. Proximity to highwalls is also critical for geological mapping, which provides valuable input data for geotechnical analysis. Geotechnical analyses are required in the mine design process to establish safe and efficient mining operations.

To manage highwall related hazards, Rio Tinto's safety standard "D3 – Management of slope geotechnical hazards standard" (Rio Tinto, 2019) prescribes, among other controls, training to employees to recognize and report highwall hazards, thorough geotechnical examinations, and plans for highwall control. Additionally, the integrity of highwalls is maintained through early detection of movement on highwalls and preventative measures, such as design changes and blasting and mining controls to avoid accidents and ensure productivity (Reeves et al., 2001).
Study on the Mechanism of Wellbore Stability and Drilling Fluid Technology Countermeasures in the Ultra-Deep Fractured Formation of Southwest Tarim Depression
Authors: Fang Zheng , Chen Mian , Li Jiaxin , Zhang Yingxi , Zhang Zhen , Ma Weizhen , Lu Yunhu , Wang Wansheng
Published: August 2024

The Southwest Tarim Depression is an important production succession area of the Tarim oilfield, but in the course of exploration, due to the complexity of ultra-deep fracture formation, the mechanism of wellbore instability is not clear, and reasonable drilling fluid technology countermeasures cannot be proposed, which brings great challenges to efficient drilling. In this paper, starting from the lithology, physical and chemical properties, microstructure and rock mechanics characteristics of ultra-deep fracture formation in southwest depression, the mechanism of wellbore instability is clarified, a suitable calculation model of wellbore stability is established, and a reasonable safe drilling fluid density window is proposed. Technical countermeasures of drilling fluid are put forward from the perspective of engineering geomechanics. The results show that the ultra-deep fractured formation is dominated by dolomite, showing weak water-sensitive characteristics and developing multi-scale fractures, which makes drilling fluid invade the formation and cause wellbore collapse. By calculating the corresponding sealing coefficient plate and safe drilling fluid density window, it is clear that when the sealing coefficient is above 0.7, the diameter expansion ratio (≤ 15%) can be kept within the safe construction range. The appropriate sealing materials can be selected to improve the sealing coefficient of drilling fluid, which can also increase the sealing property of drilling fluid and improve the condition of wellbore instability in ultra-deep fractured formations.

1. INTRODUCTION

The geological conditions of the ultra-deep fractured formations in the southwest Tarim depression are highly complex, characterized by widespread natural fractures and significant differences in structural stress. The presence of fractures, joints, and other weak planes exacerbates the anisotropy of formation strength, affecting wellbore stability. Instabilities in wellbores within fractured reservoirs are more severe compared to conventional reservoirs [1-2]. The lubricating effect generated by drilling fluid infiltration into the formation leads to a reduction in rock strength [3]. Consequently, frequent occurrences of wellbore instability accidents when drilling encounters such formations greatly impede the efficient development of oil and gas resources in the southwest Tarim depression.
Wavelet Transform and Hidden Markov Model Application for Unsupervised Clustering of Microseismic Events from CO2 Injection
Authors: Willis R. M. , Yoon H. , Harding J. L.
Published: August 2024

Injection of CO2 increases pore pressures that trigger complex subsurface interactions, leading to slip or reactivation of pre-existing faults/fractures and/or creating fractures. Understanding the subsurface response is key to preserving the integrity of the storage site, optimizing the injection, and mitigating the risk of seismic hazards. Machine learning (ML) models have shown the potential to improve our understanding of complex earth systems by identifying subtle changes in patterns of seismic and microseismic data. Furthermore, ML has shown great promise in revealing patterns in time-dependent spectral properties of (micro-) seismic data to identify differences in subsurface response. In this study, a wavelet transform scheme is implemented to isolate high energy frequency bands within microseismic data from the Illinois Basin Decatur Project (IBDP). Subsequently, an unsupervised ML method is used to identify various subsurface responses attributed to CO2 injection at the IBDP. Specifically, the unsupervised method known as SpecUFEx is used to further reduce the dimensionality of the reconstructed high energy micro-seismic spectrograms, solve for characteristic fingerprints, and apply K-means clustering to group similar fingerprints. Finally, a comparison is made between our clustering results and an implementation of SpecUFEx where the full frequency spectrum of the microseismic data was used.

1 INTRODUCTION

Carbon capture and storage (CCS) has emerged as a critical technology in the global effort to mitigate climate change by reducing carbon dioxide (CO2) emissions from industrial processes and power generation. The concept of CCS involves capturing CO2 emissions from large point sources such as power plants and industrial facilities, transporting the captured CO2 to suitable storage sites, and securely storing it underground in geological formations to prevent its release into the atmosphere. This approach not only helps reduce greenhouse gas emissions but also enables the continued use of fossil fuels while transitioning to cleaner energy sources. As nations strive to meet ambitious climate targets, CCS is increasingly recognized as a key component of the portfolio of solutions needed to achieve significant and sustained reductions in CO2 emissions on a global scale. However, one primary risk of CCS is induced seismicity. Injecting CO2 into subsurface formations increases pore pressure, leading to changes in local stress conditions and potentially triggering micro-seismic events within basement rock. Accurate monitoring and modeling are imperative for the success of CCS projects, ensuring efficiency, safety, and societal acceptance.
Growth Parameter Conditioning of Genetic Discrete Fracture Networks to Trace Length Distribution Data
Authors: Kim J. , Choi J. , Leem J. , Song J.-J.
Published: August 2024

Genetic discrete fracture network (DFN) modeling is a dynamic modeling approach that simulates fracture growth processes in DFN generation. The modeling procedure incorporates growth-related input parameters, such as the growth time, step size, and coefficients of nucleation and growth, which are difficult to deduce directly from survey data. This study introduces a method for conditioning these growth parameters to trace length distribution using an optimization procedure, where the growth parameters are fine-tuned to produce genetic DFNs that align with the observed distribution. The optimization objective function is formulated to minimize the difference in trace length distributions and the number of traces between the observed trace map and that derived from a genetic DFN. In case studies involving synthetic and real trace maps, the conditioned genetic DFNs reproduced trace maps that exhibit a high level of fitness to the observed data. Considering the representation of complex growth processes and fracture interactions, these models can provide a robust foundation for DFN extrapolation beyond the surveyed areas.

1. INTRODUCTION

Natural fracture networks can be modeled in the form of discrete fracture networks (DFNs) that capture the spatial characteristics of the observed network. In DFNs, fractures are simplified as discrete objects, commonly as disks, which replicate the geometric properties of fractures. The geometric properties of these fracture disks, including size and orientation, can be determined by analyzing the distributions of surveyed data and directly sampling values from these distributions to match the observed data. This modeling approach is termed as "stochastic" or "Poisson" DFN modeling, where fractures are randomly generated by corresponding statistical models (Lei et al., 2017).

While stochastic DFNs follow the statistical models of geometric properties, such as size and orientation, they exhibit clear limitations in reproducing the organization or topology of fracture networks, especially the specific fracture terminations in the form of T-type intersections (Selroos et al., 2022). The stochastic DFN approach fundamentally lacks physical integrity as it is purely statistical and does not consider the physical process involved in fracture network generation.
Numerical Simulation of Toppling Failure in Sedimentary Rock Slope Cuts with Alternating Soft and Hard Bands
Authors: Ashraf M. , Emad M. Z. , Waqas M. , Moazzam H.
Published: August 2024

Rock slope stability is a major concern in mega engineering projects, and it has been a major focus of engineering geology for over three centuries. The toppling failure mode is considered as one of the most complex and challenging to stabilize. The complexity of slope failures increases with a combination of mechanisms and the presence of different geological units and structures. Numerical modeling is a powerful tool for analyzing and simulating rock slope stability. This paper aims to assess and propose stabilization methods for toppling failure and complex toppling failure, using numerical modeling software FLAC 2D. The paper introduces a technique for assessing toppling failure in alternating soft-hard rock bands during adverse conditions and proposes innovative stabilization methods based on simulation effects. The results suggest that numerical modeling software can effectively assess toppling failure, design support, and reinforcement methods, and help predict and reduce the risk of slope collapse in toppling zones through appropriate stabilization techniques.

1. INTRODUCTION

The stability of rock slopes, as explained by Hoek (1981), is a critical aspect of numerous geotechnical engineering endeavors, owing to their susceptibility to failure triggered by diverse factors such as geological conditions (Wyllie and Mah, 2004), environmental forces, and material properties. Rock slope failures can result in severe consequences, encompassing loss of life, infrastructure damage, and economic disruption (Evans, 2006).

For over three centuries, engineering geology has been truly involved in investigating slope stability, which delineates capacity of a slope to withstand internal and external forces without collapsing (Azarafza, 2021). This aspect remains a captivating and expansive domain, encompassing various manifestations of rock and soil failures, as expounded by Li (2022). Ensuring the safety of individuals and structures necessitates the deployment of dependable and precise methods for assessing rock slope stability. Understanding the prevailing failure mechanisms and delineating stable and unstable zones within a slope are pivotal prerequisites for accurate assessment (Mat, 2023). Hoek (1981) categorizes simplified failure modes into four types: plane, wedge, circular, and toppling.
Examining the Anisotropic Strength of Plain and Steel Fiber Reinforced Shotcrete
Authors: Khan M. U. , Waqas M. , Emad M. Z. , Tahir M. U.
Published: August 2024

Shotcrete, a crucial component for initial rock support in underground mining and civil projects, significantly influences the adequacy of support systems. Evaluating the strength of shotcrete involves conducting uniaxial compressive strength (UCS) tests on the extracted core samples. Typically, shotcrete cores are obtained along the direction of application, leading to an oversight of its strength perpendicular to this direction. Consequently, the true bearing strength of shotcrete is neglected, despite higher stresses acting normal to the application direction. While the anisotropic behavior of shotcrete is documented, comprehensive studies on this scale and nature are lacking. This research addresses this gap by presenting extensive testing of shotcrete cores extracted from tunnels of a mega hydroelectric project in Pakistan. The study encompasses 7 and 28-day strength tests of shotcrete cores, shedding light on the often-overlooked perpendicular strength. Additionally, the investigation extends to the anisotropic behavior of steel fiber-reinforced shotcrete, revealing that shotcrete exhibits increased strength perpendicular to its application direction. This exploration contributes valuable insights to the understanding of shotcrete behavior, emphasizing its multifaceted strength characteristics.

1. INTRODUCTION

The New Austrian Tunneling Method (NATM) has revolutionized underground construction by advocating for controlled deformation of the host ground during excavation (Boldini et al. 2005; Zhang et al. 2018). This innovative approach employs a thin layer of sprayed concrete, commonly known as shotcrete, to reinforce the tunnel walls and reduce the load on the final linings or subsequent rock support elements. Shotcrete serves as a versatile and effective initial rock support component, sealing fissures and cracks while preventing further disintegration and weathering of the surrounding rocks (Galan et al. 2019a; Galan et al. 2019b). By providing a protective barrier, shotcrete enhances safety for workers and facilitates smoother excavation cycles, instilling confidence in laborers as they advance into new phase of construction (Reny and Ginouse 2014) (Ginouse et al. 2015; Lemay et al. 2014).

The significance of shotcrete in tunneling cannot be overstated. Shotcrete acts as a critical component in the initial support system for underground constructions, offering stability and durability to tunnel walls. Its versatility and adaptability make shotcrete an indispensable tool for tunneling operations, particularly in challenging geological conditions where ground stability is a concern.
Multi-Source Data Fusion and Knowledge Presentation for Shield Tunnel Maintenance Work Based on Knowledge Graph
Authors: Pang H. J. , Zha C. C. , Jia F. , Xue Y. D.
Published: August 2024

The study tackles operational challenges in shield tunnel maintenance, focusing on multi-source date fusion and decision-making suggestion. Employing a multi-disciplinary approach spanning civil engineering, artificial intelligence, and engineering management, the study establishes an intelligent decision-making system based on knowledge graph for shield tunnel maintenance work. Firstly, a multi-data processing program is developed for dealing with multi-source tunnel data, encompassing diverse dimensions reflecting the structural state of shield tunnels. Comprehensive perception of tunnel structure state is achieved through the integration of tunnel internal surface images and 3D point cloud information. Secondly, to address the specialized expert knowledge and experience in tunnel maintenance work, the study explores methods for knowledge representation, extraction, and integration. Leveraging several natural language processing techniques, including ontology and semantic rules. Lastly, a knowledge graph for shield tunnel maintenance is then constructed by Neo4j, integrating data from both multi-source tunnel data and expert knowledge to quantify tunnel structural health and formulate operational strategies for maintenance work. Through the case study, the tunnel knowledge graph is demonstrated to be effective and advanced in tunnel maintenance work.

1. INTRODUCTION AND BACKGROUND

In recent years, China's major cities have experienced significant and rapid development in their urban metro systems, aiming to enhance urban transport capacity and address the commuting needs of residents. Zhang et al. (2023) reported, by December 31, 2023, the urban metro network in China extended to 11,232 km, facilitating 23.71 billion passenger trips, resulting in an annual passenger turnover of 197.8 billion trips per kilometer. The growth in urban metro mileage is visually represented in Fig.1. Since 2013, the operational mileage of China's urban metro systems has consistently increased, demonstrating a rising annual growth rate and robust development in domestic urban rail transit. Fig.2. illustrates the total operational rail transit mileage for major cities in 2023, with Shanghai leading with a total of 965 km.

Situated on the eastern coast of China, Shanghai, as a developed city, relies significantly on its transportation infrastructure to ensure normal urban operations. The operation of the urban metro service exposes the metro tunnel structure to various risk factors, including periodic train loads, segment aging, and surrounding construction activities.
Numerical Analysis of Fracture Propagation Behavior in Hard Rocks Subjected to Radial Borehole Fracturing Based on the Combined Finite-Discrete Element Method
Authors: Zou Wenchao , Huang Zhongwei , Wang Zikang , Wu Xiaoguang , Zhang Xu , Xie Zixiao , Li Kun , Huang Pengpeng , Tan Hui , Qin Xinyu
Published: August 2024

Hydraulic fracturing is an important stimulation technology to achieve high and stable production in deep and ultra-deep reservoirs. However, there are currently numerous complex technical problems, such as high breakdown pressure, single fracture and uncontrollable. To addressing those issues, a novel stimulation, radial borehole fracturing has been proposed. To have a clear understanding of the radial borehole fracturing performance, a 3D Finite-Discrete Element Method model of radial borehole fracturing is established in this paper. Then, the applicability of the HM coupled FDEM model was validated by laboratory experiments. The results indicate that when horizontal stress difference ratio is 0.4, radial borehole fracturing has a significant guiding effect on fracture propagation behavior. Radial borehole fracturing creates fractures with larger tortuosity and aperture. Compared to conventional fracturing, the breakdown pressure of hard rock in radial borehole fracturing is 9.1%∼14.1% lower. As Young's modulus increases, the guidance of radial borehole and the complexity of fracture network strengthen. The present study is expected to provide a theoretical foundation for applicability of radial borehole fracturing in deep and ultra-deep reservoirs.

1. INTRODUCTION

The deep and ultra-deep oil and gas resources are rich and widely distributed in China, accounting for 35% of the total oil and gas resources (She, 2024). In recent years, important breakthroughs have been made in exploration, which has rapidly attracted wide attention of scholars. These reservoirs possess distinctive geological features, characterized by high temperatures and pressures (Lei et al., 2021). The rocks exhibit traits such as high density, high hardness, strong heterogeneity, and high compressive strength. Consequently, there are currently numerous technical problems to be solved in the process of reservoir stimulation in deep and ultra-deep wells, such as high breakdown pressure, single fracture and uncontrollable (Zhang et al., 2023; Li et al., 2021). Therefore, an innovative stimulation method is proposed to address the above problems.

Radial borehole fracturing is a kind of reservoir stimulation technology that carries out hydraulic fracturing on the basis of drilling radial boreholes, which can significantly reduce the formation breakdown pressure and guide fracture directional propagation (Guo et al., 2022; Guo et al., 2016). Field tests conducted in geothermal and coal formations have demonstrated substantial enhancements in reservoir permeability with the application of this innovative technology (Chen et al., 2017; Nair et al., 2017; Ouadi et al., 2024).