bluuebunny/crossref_metadata_2025_split huggingface dataset:
A New Method for Evaluating Radionuclide Migration in Groundwater
Authors: Feng Shengyang , Chen Xiaojie , Jiang Yourui , Tang Hao 
Published: September 2022

ABSTRACT:
The purpose of this study is to propose a new method for evaluating the migration of nuclides of uranium tailings paste backfill in groundwater. Uranium tailings reservoir is a significant threat to the nearby environment and the health of residents. Filling the uranium tailings paste backfill into the mine goaf can effectively reduce the impact of uranium tailings on the surrounding environment. However, there is still a lack of effective methods to evaluate the effect of radionuclides in uranium tailings paste backfill on groundwater. Uranium tailings paste backfill was made from the samples collected from a uranium tailings reservoir, and leaching experiments were carried out to obtain a variation curve of uranium concentration. The fractal parameters of rock fractures are obtained from the goaf of a gypsum mine exploration. The discrete fracture network model (DFN) of underground rock mass in the goaf is established according to the fractal parameters. When the results of leaching experiments are introduced into the numerical simulation model, it is found that when the local water is in the flow state, the flow direction of uranium is consistent with that of groundwater and is related to fractures.

1. INTRODUCTION
Mining is extracting underground resources and can be divided into open-pit and underground mining depending on the mining method. The mining process generates a large volume of tailings and void areas and releases hazardous substances into the surrounding environment. The threat to the surrounding environment from tailings and voids does not end with mining (Yilmaz and Yumlu, 2017). The pollution of the surrounding environment by tailings, especially uranium tailings, is obvious. Although uranium in uranium tailings has been extracted, there are still a lot of harmful substances in the tailings. These harmful substances can be carried into the environment by dust and groundwater and enriched into the human body through the food chain, posing a threat to human health. What’s more, the dams of uranium tailing reservoirs may be destabilized by extreme weather or seismic activity, and a large volume of tailings in the ponds may break through the constraints of the tailings dams under gravity, with disastrous consequences for the lives of the surrounding residents and the environment.
Numerical Mesh Sensitivity Works Performed to Analyze Advective Gas Flow in a Compact Clay
Authors: Damians I. P. , Noghretab B. S. , Olivella S. , Gens A. 
Published: September 2022

ABSTRACT:
In this work, the suitability of several meshing strategies to optimize the CPU time consumption is investigated. The mesh sensitivity strategy is established by applying the basic framework of a coupled hydro-gas-mechanical 3D FEM numerical model to simulate the tests in terms of types of the elements, number of elements and nodes to quantify the influence of different meshes on the accuracy of the test results with regard to optimization of the CPU time consumption. In this study, the problem is represented and the performance and calculation time of both element types and mesh size in the utilized 3D FEM model are checked. To achieve this, both tetrahedral and hexahedral meshes and their refinement/coarsening are generated. Then the performance of the element types and sizes on the test results are compared. This is a main issue for modelling gas injection through clay-based engineered isolation barriers that requires clear up-scaled tests due to full-scale experiments.

1. INTRODUCTION
To quantify the physical properties of a phenomenon such as fluid flow, heat transfer, mass transport, and wave propagation, mathematical equations must be utilized. The finite element method (FEM) is a general numerical method that is the most widely used approach for numerically solving engineering problems (partial differential equations) in 2 or 3-dimensional variable space. In order to calculate the solution in the FEM method, the domain must be divided into a discrete number of elements which is referred to as mesh generation. Striking a balance between accuracy and speed is challenging. A large continuous medium can have infinite degrees of freedom (DoF), as a result, to do the FEM modelling, the meshing approach (mesh size and type of element) is the key component to acquire the most accurate and reliable outcomes in the finite element modelling (Cavin et al., 2005). Accuracy depends on both mesh size (the total number of elements) and element type (the shape of individual elements). Mesh size typically refers to the CPU time consumption. The smaller the mesh size becomes the more accurate the result achieves, hence in larger simulations required solving time of the model extends. To achieve the best balance of accuracy and solving time, mesh coarsening (refining) is required.
Horizontal Well Orientation Optimization Based on the Integration of Hydraulic Fracturing Network Simulation and Productivity Prediction
Authors: Qian Wang , Shengxian Zhao , Chenxi Ye , Wenbao Zhai , Chao Fang , Peng Tan 
Published: September 2022

ABSTRACT:
Horizontal drilling and large-scale hydraulic fracturing are currently used to increase artificial fracture networks and per well production in unconventional reservoirs. Due to the differences of regional geological characteristics, natural fracture characteristics and geomechanical characteristics, different wellbore directions may lead to different hydraulic fracturing effects and post-frac productivity. If the well orientation is not correct, it can result in poor hydraulic fracturing propagation and inefficient production. The high precision geological model and geomechanical model of platform of typical shale gas blocks in Sichuan were established. First, considering the interaction of hydraulic fracture and natural fracture, interaction of hydraulic fracture each other, hydraulic fracturing network distribution in different in-situ stress orientation, natural fracture azimuth, wellbore azimuth combination cases were simulated. Second, high-precision unstructured grid numerical model was established on the basis of hydraulic fracturing fractures to accurately characterize fracture network morphology and fracture conductivity. The flow characteristics of hydraulic fracturing network was simulated, and post-frac productivity were predicted. Finally, the optimal wellbore orientation under various in-situ stresses and natural fracture combination cases was obtained by combining the fracturing effect and post-frac productivity. The research results show that, under the typical fracturing construction and production conditions in Sichuan shale gas block, the optimal well orientation is not affected by the natural fracture orientation. The fracturing effect and production within the range of 0-30 degrees of horizontal minimum in-situ stress are better. When the angle between natural fracture orientation and horizontal minimum in-situ stress is more than 50°, the overall production becomes better in various well directions.

1. INTRODUCTION
Hydraulic fracturing in horizontal well can greatly improve the production capacity of a single well in unconventional oil and gas resources. Due to regional differences in geological characteristics, natural fracture characteristics and geomechanical characteristics of unconventional reservoirs, variability in in-situ stress directions, natural fracture directions and wellbore directions may lead to different fracturing effects and post-frac productivity under the same fracturing construction and production conditions. Therefore, it is very important for horizontal well orientation optimization.
Stress Relaxation Tests on an Outcrop Shale
Authors: Fjær E. , Stenebråten J. F. , Larsen I. , Lozovyi M. , Holt R. M. 
Published: September 2022

ABSTRACT:
Numerous observations have shown that shale formations may creep in and close the annulus between rock and casing in deep wells, thus effectively sealing off the well sections in a natural way. This movement of the rock is partly controlled by strain and partly by stress, and parts of the rock may be in a post-peak state while other parts are in a pre-peak state. The effect of pre-peak versus post-peak conditions on creep characteristics was studied in a set of stress relaxation tests on Pierre II shale. It was found that the stress relaxation process can be described with great precision both by a logarithmic function and a power-law function. However, only the power-law function fulfills the expected asymptotic behavior for infinite time. Temperature fluctuations can be accurately accounted for by an Arrhenius-type factor. The shear stress relaxation appears to be insensitive to pore pressure alterations. There is an indication that the relaxation rate is slightly higher when the rock is in a strain hardening state than in a strain softening state. No significant effect of exposure to NaOH was seen on the relaxation process.

1. INTRODUCTION
Completion of oil and gas wells often implies that the annulus between rock and casing is left open in long sections. Such sections are potential pathways for leakage from the reservoir to the surface and needs to be sealed off at selected spots prior to plugging and abandonment. It is however a frequent and highly welcome observation that shale formations creep in, closes the annulus, and thus form a natural barrier that seals the well (Williams et al., 2009; Kristiansen et al., 2018). There are limited possibilities to monitor this process in the field as it goes on behind the casing, but the terminal state is nevertheless of great importance since it governs the long-term sealing efficiency of the barrier. It is therefore interesting to study long-term shale creep under controllable laboratory conditions.
3D Hydro-Mechanical Modeling of Shaly Caprock Response to CO2 Long-Term Periodic Injection Experiment (CO2LPIE)
Authors: Sciandra D. , Rahimzadeh Kivi I. , Vilarrasa V. , Makhnenko R. , Jaeggi D. , Rebscher D. 
Published: September 2022

ABSTRACT:
Carbon capture and storage in deep geological formations is necessary to achieve a meaningful reduction of anthropogenic CO2 emissions into the atmosphere. Given the buoyancy of the injected CO2, it is essential to adequately characterize the sealing caprocks commonly comprised of clay-rich formations, including shales. If the inherent anisotropy of shales is not considered, model prediction errors will propagate with time and space. To limit errors, the accurate experimental laboratory measurements should be scaled up and the in-situ behavior of the caprock should be studied in detail. Underground rock laboratories (URLs) offer a unique opportunity to investigate the caprock sealing capacity at a few meters scale in a well-defined and well-monitored environment. This perspective applies to the CO2 Long-term Periodic Injection Experiment (CO2LPIE) at the Swiss Mont Terri URL. In the experiment, it is planned to inject gaseous CO2 into Opalinus Clay, which is considered as a representative caprock for underground storage. Opalinus Clay shows large-scale anisotropic behavior due to the presence of bedding planes and heteorogeneities. We numerically simulate the CO2LPIE experiment using a 3D hydro-mechanical model and assuming linear poroelastic transverse isotropic behavior of the rock. We find that the CO2 is unlikely to penetrate the rock in free phase, while the diffusive front of dissolved CO2 in resident brine hardly propagates half a meter after two years of injection. The overpressure and induced deformation and stress changes preferentially develop along the bedding planes, although not sufficiently to lead to shear failure.

1. INTRODUCTION
To limit global warming to 1.5 °C, net carbon removal after 2050 should be targeted (IPCC, 2014). To reach this goal, it is critical to develop novel technologies and a promising approach is Carbon Capture and Storage (CCS). CCS is generally understood as the set of CO2 capture from a large stationary source, transport to an injection site, and permanent storage in the subsurface (Benson and Cook, 2005). CO2 density at the pressure and temperature of typical underground storage formations in sedimentary basins is approximately 65 % of the in-situ brine density. As a result, the plume of the injected CO2 will not only migrate outwards from the injection well, but also upwards until it finds a sealing layer called caprock (Tsang and Niemi, 2017). To assure long-term CO2 trapping, it is of fundamental importance to properly characterize the caprock sealing capacity, commonly presented in terms of permeability, porosity, capillary entry pressure and relative permeability curves, and their evolution with time (Kaldi et al., 2011).
Inertia Dominant and Transient Flow in Fractures - Beyond the Cubic Law
Authors: Gee B. , Gracie R. 
Published: September 2022

ABSTRACT:
There are many applications which require a fracture flow model that accounts for variations in aperture beyond surface roughness. Large-scale models and simulations of fluid flow through fractures are almost exclusively based on the cubic law (Poiseuille flow) for steady-state flow through rigid parallel plates. When the fracture aperture is time and/or spatially varying, flow is transient, and/or flow rates are modest (Re≥1), cubic law predictions can deviate substantially from true fluid behaviour. In this paper, we present a new Reduced Dimension Fracture Flow (RDFF) model which more accurately predicts transient flow for incompressible fluids with modest Reynolds numbers through fractures with time and/or spatially varying aperture. The RDFF model is derived from the two-dimensional Navier-Stokes equations and yields a two-field model (fluid flux and pressure) governed by the conservation of mass and momentum. The RDFF model is shown to conserve energy in spatially varying fractures where the cubic law does not. We demonstrate that the RDFF model captures complex transient and inertial behaviours not previously captured for flows with modest Reynolds numbers (1≤Re≤100) and demonstrates up to 400% improvements in error over the cubic law in steady-state flow conditions through fractures with sinusoidally varying aperture.

1 INTRODUCTION
Large-scale simulations of flow through fractures rely almost exclusively on the Poiseuille flow model, also known as "the cubic law". The cubic law is the analytical solution to the Navier-Stokes equations for steady flow of an incompressible fluid through parallel plates. It provides a constitutive equation linking the pressure gradient to the fluid flux according to the relationship
(Equation)
in which p is the pressure, μ is the kinematic fluid viscosity, w is the fracture aperture, and q is the fluid flux. In hydro-mechanical models with deformable fractures, such as hydraulic fracturing or enhanced geothermal energy, the cubic law is often combined with the conservation of mass derived from a fracture-scale control volume:
(Equation)
in which q is the flux from the cubic law. Despite the assumption that the cubic law applies for rigid parallel plate geometries, the conservation of mass allows both time and spatially varying apertures.
Experimental Investigation of Desiccation Behavior in Inorganic Microfiber-Reinforced Engineered Barrier Materials (IMEBM) for Geological Repository of Nuclear Spent Fuel
Authors: Grasley Julia , Rahmani Mohammad , Azzam Abdullah , Nsengiyumva Gabriel , Kim Yong-Rak , Eun Jongwan , Kim Seunghee 
Published: September 2022

ABSTRACT:
Secure storage of nuclear spent fuel is of great concern for protecting public health and safety. The standard long-term solution for nuclear waste disposal is containment in geological repositories. Nuclear spent fuel, stored in canisters, is placed deep underground with one or more Engineered Barrier Materials (EBM) forming a buffer between the waste containers and the natural rock. Bentonite clay is commonly used as an EBM for its low cost, long-term stability, low hydraulic permeability in a saturated state, high thermal resistance, high radionuclide retardation capacity, high swelling pressure, and "self-healing" capability. However, bentonite clay subjected to heating from nuclear waste decay may undergo desiccation cracking. In this study, inorganic microfiber reinforcement was evaluated as a method of reducing desiccation cracking in EBM. A restrained ring test method for soils coupled with digital image correlation (DIC) was employed to capture free shrinkage and desiccation cracking. Reinforcement of bentonite clay with 1.0 % wt. basalt fibers was shown to be effective in reducing crack propagation and separation.

1. INTRODUCTION

1.1 Research Significance
Each nuclear power reactor generates 20-30 tons of highly radioactive waste, annually. Secure long-term storage of nuclear waste is a great concern for public health and safety. A preferred long-term solution for highly radioactive waste disposal is containment in geological repositories. Canisters filled with radioactive waste are placed in tunnels, with one or more Engineered Barrier Systems (EBS) encapsulating them.
A material like bentonite clay, which is physio-chemically compatible with both natural rock and nuclear waste, can be used in EBS. In fact, bentonite is preferred as an Engineered Barrier Material (EBM) for its advantageous properties including low cost, long-term stability, low hydraulic permeability and conductivity in a saturated state, high thermal resistance, high radionuclide retardation capacity, high swelling pressure, and good "self-healing" capability. However, heat-induced desiccation cracking of bentonite can cause transmission of radiation in EBS (Allen & Wood, 1988; Bharat et al., 2017; Hirose & Matsubara, 2018; Mohammad, 2020; Soujanya & Thyagaraj, 2017).
Salt Cavern Dissolution Mining: Lessons Learned from Simulations
Authors: Li Li , Gracie Robert , Dusseault Maurice 
Published: September 2022

ABSTRACT:
Salt caverns are usually developed by circulating fresh water through a well in a salt formation and extracting brine. Due to the difference in density (buoyancy), fresh water quickly rises to the top of the cavern and promotes dissolution, so the shape of the cavern can be controlled in part by an air pad at the top of the cavern. Relatively high fluid velocities and buoyancy lead to the creation of vortices that are shown to play a critical role in cavern development. Vortices induce higher localized rates of dissolution, leading to complexity which has traditionally been thought to be exclusively due to heterogeneity of the salt formation. Using a combination of simulation based on a novel method involving full CFD and physical-driven dissolution front evolution, we demonstrate how flow complexities combined with the non-reversible nature of salt dissolution drive cavern shape complexity. We discuss and compare mechanisms observed in terms of concentration distributions, brine flow patterns, dissolution rates, and the non-linear impact of injection rate and insoluble interlayer on cavern shape and size.

1 INTRODUCTION
The increases in renewable energy generation promote a high demand for large energy storage facilities. Compressed Air Energy Storage (CAES) is considered one of the best options because it has the advantage of possessing a large storage capacity, small energy loss rate, relatively high cycle efficiency, and is environmentally friendly (Li et al., 2018). A large compressed air storage reservoir is key to ensure the CAES system performs large-scale energy storage, and cavern stability is needed for storage security. Salt formations provide favourable conditions for large-scale cavities because the salt rock has low permeability and excellent self-healing characteristics (Chen et al., 2013; Ozarslan, 2012), ensuring air tightness. However, during the construction of the salt cavern by dissolution mining, overhanging blocks will develop, and the failure of these blocks can threaten the utility of the cavern (Wang et al., 2017). Although different technologies, such as blanket application with sonar monitoring, are used to control roof dissolution and help optimize cavern shape, caverns with high irregularity, as sketched in Fig. 1 are still commonly constructed. So, the key factors that affect the dissolution of solid minerals should be investigated in order to guide and execute effective cavern shape control. Numerical simulation is an efficient way to investigate the factors, especially for large cavern dissolution, which is challenging to explore through laboratory or field experiments.
Experimental Investigation to Fabricate Synthetic Laminated Rock with Different Bedding Plane Cohesive Strengths
Authors: Shi Qingwen , Mishra Brijes 
Published: September 2022

ABSTRACT:
Bedding plane properties influence the failure behavior of laminated rocks such as slate and shale. For safe and stable underground coal mine design it is imperative to understand the relationship between the bedding plane strength and the failure of laminated rock. However, it is difficult to obtain in situ laminated rocks with various bedding plane properties while keeping other properties constant. In the present research, we experimentally investigated various approaches to vary the weak plane cohesive strength (Cp). Concrete block incorporating a weak plane was casted and the Cp of the weak plane was varied experimentally using two methods. Direct shear tests along the planes validated that applying normal stress on the concrete block successfully varied the Cp. The verified method was then used to cast synthetic laminated rock (SLR) with various Cp. We then conducted Brazilian splitting tests on SLR with different orientations of bedding planes and compared the failure strength and failure modes with that of shale specimen. The results validated the second method as both failure strength and failure modes of SLR specimens matched the behavior of shale specimens. This research provided a validated method to fabricate SLR with different Cp in the laboratory.

1. INTRODUCTION
Bedding planes cause anisotropy and strength reduction of laminated rocks such as slate and shale. Laminated rock-caused roof failure has caused numerous fatalities in the underground mining industry 1-6. Shi and Mishra summarized historical research on laminated roof failure in underground coal mines 5. Bedding plane properties influence the stability and mechanical behavior of laminated roof. In practical engineering applications, especially in underground coal mining, it is imperative to understand the relationship between the bedding plane properties and the laminated rock failure. For example, a laminated shale roof exposed in underground entries at two longwall coal mines in the eastern US extracting the lower Kittanning coal bed. Although geological conditions such as in situ stress, longwall panel layout, and uniaxial compressive strength of shale roof are similar, the stability of the laminated roof at these two mines differs significantly due to the distinct bedding plane properties7.