bluuebunny/crossref_metadata_2025_split huggingface dataset:
FDEM Modeling of PDC Cutter-Rock Interactions for Geothermal Drilling Applications
Authors: Heilman E. , Euser B. , Frash L. , Meng M. , Li W. , Lei Z. , Rougier E. 
Published: August 2024

ABSTRACT:
We aim to model PDC cutter-rock interactions in 3-D through numerical study to find an optimal arrangement of parameters for efficient geothermal drilling. Using the combined finite discrete element method (FDEM), we model realistic pressure conditions and rock fracture and fragmentation. FDEM can model both continuum and discontinuous mechanical behavior, which allows for modeling of fracture in targeted rock at downhole conditions. We simulate PDC cutter-rock interaction in 3-D for a range of back rake angles, cutting speeds, and depth of cuts using granite as our target rock material. These parameters are varied to investigate the impact on the cutting force and fracture dynamics in an effort to benchmark performance. We reproduce results from numerical rock cutting tests and qualitative results from laboratory experiments. We report on the progress of the numerical analysis for this complex multi-physics problem.

1 INTRODUCTION
Geothermal energy is an important form of clean energy in the United States and other parts of the world. Geothermal energy drilling involves deeper, hotter, and harder rock sources than conventional/unconventional oil and gas targets (Dwivedi et al., 2008; Kumari et al., 2017). Understanding the mechanics of geothermal energy drilling is essential to reducing the overall cost, of which drilling can be over half of the total cost (Pierce and Livesay, 1994). A commonly used drill bit due to its strength and resistance to abrasive wear is the polycrystalline diamond compact (PDC) cutter bit (Dougherty et al., 2014; Yang et al., 2018). The combination of deep, hard rock means the forces in geothermal drilling are typically larger and drilling performance needs to be increased. The rate of penetration (ROP) determines the efficiency of drilling, as in how much rock material can be removed. A high ROP would remove more rock material, however, higher ROP means higher forces on the drill bit. Determining the forces on the drill bit under a geothermal drilling interaction allows us insight into drilling performance.
Physical Models of Dry Masonry Retaining Walls
Authors: R. Alejano, L. , I. Pérez-Rey, , Muñiz-Menéndez M. , Ding B. D. 
Published: August 2024

ABSTRACT:
Physical models are a sound tool for verifying some instability mechanisms. The authors apply these physical models to check the stability analysis of traditional dry granite masonry retaining walls as built in NW Spain. Unlike concrete retaining walls, dry masonry ones should be designed to ensure not only general stability but also an intrinsic one, since they can fail due to sliding through masonry contacts or to toppling mechanisms of parts of the wall. Accordingly, first, unfilled scaled retaining walls made up of small granite slabs are tilted until failure is observed, in this case due to toppling, following a stepped path. Secondly, simple retaining walls made of granite slabs are filled with sand of known friction angle until failure. In both cases, analytical expressions are applied to the model at stake, showing a rather good accuracy in predicting the observed phenomena. Some ideas are finally provided suggesting aspects that need a rigorous knowledge when applying the formulation to large size real cases.

1. INTRODUCTION
In the words of Professor Einstein (2023), physical models are very suitable tools for verifying analytical models and the actual response of rock against specific failure mechanisms. Once verified, numerical approaches can help to expand the variation of parameters tested and carry out advance studies (back-analysis or sensitivity). Popular in the past, physical models are now hardly used by the rock mechanics community, probably due to cheaper numerical modeling options. However, they present some advantages in relation to modern numerical approaches.
In this brief study, the authors present some rather simple physical lab-scale models of dry masonry retaining walls that were used first to identify the failure mechanism at stake and then to provide a verification of analytical formulations proposed elsewhere.
The authors presented a study on the behavior and stability of traditional retaining drystone granite walls as traditionally built in Galicia, the northwest region of Spain (Alejano et al. 2012a and b). These structures are still commonly in use in this region for building and road construction, and occasionally, they achieve heights well over 10 m. They are generally cheaper and less environmentally aggressive than concrete walls and present an excellent landscape integration (Pozo et al., 2013), generating a low environmental impact, since the material used often comes from waste or low-price material from granite quarries producing large blocks for the ornamental stone market in the region.
Analysis of Shear Slip Ahead of Hydraulic Fracture Along a Frictional Interface Not Aligned with Principal Stresses and Conditions for Secondary Branching
Authors: Weng X. 
Published: August 2024

ABSTRACT:
Stress field at the trailing edge of the shear-slip zone ahead of a hydraulic fracture (HF) traveling along a natural fracture (NF) not aligned with maximum horizontal stress is studied in the context of its potential for inducing secondary fracture branching from the NF. The size and amount of shear-slip and the stress parallel to the NF wall are computed. Localized tensile stress occurs at the trailing edge of the shear-slip zone, with a logarithmic singularity which is similar to the elastic solution for a half-space subjected to a surface shear traction. The induced tensile stress may lead to a small surface crack being nucleated and HF branching away from NF. From the stress solution, maximum stress intensity factor K1max at the tip of a prospective crack and its corresponding length are estimated. If K1max is greater than fracture toughness, a crack can be nucleated. Example cases show that crack initiation strongly depends on HF length, NF angle, coefficient of friction and stress anisotropy. Crack initiation occurs only when HF reaches a sufficient length since the shear-slip zone length is proportional to HF length, which in turn affects K1 at the crack tip.

1. INTRODUCTION
Interaction of a hydraulic fracture (HF) and a weak interface, which can be an open or poorly cemented natural fracture (NF) or a bedding plane and is hereafter referred to as a NF in general, plays an important role in fracture stimulation of unconventional formations. When a HF intersects a NF, the interaction may result in HF crossing NF directly or with an offset (also referred to as a step-over), or being arrested by the NF. In the latter case, HF can dilate and propagate along the NF if fluid pressure exceeds the normal stress on the NF. The crossing/arrest behavior at the moment of fracture intersection has been extensively studied. Various empirical/theoretical criteria had been investigated and proposed (Warpinski and Teufel (1987), Blanton (1982, 1986), Renshaw and
Pollard (1995), Gu and Weng (2010), Gu et al. (2011), Chuprakov et al. (2013)) and been incorporated in complex fracture network models (Weng et al. (2011), Weng et al. (2016)). The understanding of a HF crossing a weak interface with an offset is somewhat limited. Cooke and Underwood (2001) studied numerically the stress parallel to the interface on the opposite wall ahead of the tip of a vertical HF approaching a weak bedding plane. They attributed the initiation of offsetting fracture to tensile peaks in the stress on both sides of the intersection point due to local interfacial opening and slippage near the intersection point for "moderate-strength" interfaces. These peaks move closer together and their magnitude increases as the distance between the fracture tip and the interface becomes small, and they occur in the shear-slip region ahead of the opening segment. Fracture offset has also been studied numerically by Thiercelin and Makkhyu (2007), and Chuprakov et al. (2010).
Hyper Fast THMC Well Integrity Simulator for Powering Optimization, Sensitivity and Risk Analysis
Authors: Kostorz W. , Le Blevec T. , Joulin C. 
Published: August 2024

ABSTRACT:
A semi-analytical approach to three-dimensional Thermo-Hydro-Mechanical-Chemical (THMC) well integrity simulations is discussed. The method extends previous plane-strain thermo-poroelastic models under a set of realistic assumptions and combines analytic and numerical solutions in a single framework. Non-analytical components of the model are resolved via one-dimensional Finite Difference schemes, and coupled with pen-and-paper solutions via simple numerical integration schemes. Time-dependent material properties of hydrating cement are taken into account in the incremental problem formulation and all model components are fully coupled. The proposed formulation is demonstrated to be in very good agreement with sophisticated FEM software, while the simulation run times are reduced by several orders of magnitude. Natural applications of the methodology proposed include high-volume workflows relying on thousands or more simulation runs (sensitivity studies, optimisation, Monte Carlo methods etc.).

1 INTRODUCTION
Well integrity is essential in many engineering applications, including CO2 storage, well plugging & abandonment, geothermal energy, oil & gas and gas fuel storage (CH4 and H2). There is a clear need from the industry for a computational well integrity assessment tool which is efficient, robust, can work with limited data sets and/or high uncertainties, and fits well within a risk-based statistical approach.
From the point of view of computational mechanics, well integrity is primarily controlled by the internal stresses within different materials comprising the well structure; these typically include metal casings surrounded by cement sheaths and the formation. Historically, two primary approaches have been undertaken to model the relevant stress responses. On one hand, the Finite Element Method (FEM) is widely used due to its flexibility and generality, in particular the natural capability of working with realistic geometries. Alternatively, idealised axisymmetric analytic models (often limited to two dimensions) have been studied by multiple authors Onaisi et al. (2017); Gholami et al. (2016); Joulin et al. (2022); Li et al. (2016); Bai et al. (2015). FEM and two-dimensional analytic models mark two ends of a spectrum; FEM is general and flexible but computationally expensive, while analytic models are ‘near-free’ computation-wise but oversimplified.
Methodology for Constructing Three-Dimensional DEM Model of Rock Specimen from CT Scan
Authors: He Changdi , Mishra Brijes 
Published: August 2024

ABSTRACT:
Developing numerical simulation models that accurately represent actual features of rocks, including the distribution of minerals, voids, and fractures, is crucial. The advancement in non-destructive evaluation methods, especially X-ray computed tomography (CT), allows for detailed analysis of the internal structures of rocks. This study uses the Res-VGG-UNet deep learning model to segment CT images, distinguishing between components that appear similar but are distinct. Integrating the findings from deep learning into PFC3D software enables the creation of rock models that truly mimic the features of actual samples. The simulation results obtained from these PFC3D models show a high degree of agreement with experimental outcomes, highlighting the effectiveness of these methods in developing accurate rock numerical models.

1 INTRODUCTION
The mechanical properties of rocks are essential for engineering applications (Jin et al., 2020), including, but not limited to, geological storage of radioactive wastes (Gibb, 1999), enhanced oil recovery (EOR) (Thomas, 2008), and the extraction of deep geothermal energy (Zimmermann and Reinicke, 2010). The determination of these properties typically involves a combination of experimental and numerical methodologies, with numerical simulations being widely used for their cost-effectiveness and time efficiency (Gentilini et al., 2013). Among the numerous techniques available for modeling the mechanical behavior of rock, the finite element method (FEM) and discrete element method (DEM) have emerged as powerful tools.
In the realm of FEM, some researchers have developed ABAQUS numerical models to explore the mechanical behavior of rock bolts bonded with different materials (Małkowski et al., 2023). Others have also applied FLAC3D for simulating both stable and unstable rock failures, implementing a constitutive law that incorporates a softening component, specifically the strain softening model (Kias et al., 2011). From the perspective of DEM, three-dimensional distinct element code (3DEC) bonded block models (BBM) are used to conduct numerical simulations (Corkum et al., 2024). These simulations assessed the behavior of a randomly discontinuous jointed rock mass subjected to a range of isotropic and devia-toric (shear) loading conditions. Particle flow code 3D grain-based models (PFC3D-GBM) integrated the specific mineral composition and grain size distribution of marble, considering the interactions both between and within the mineral grains (Zheng et al., 2023). Moreover, coupled analysis methods are increasingly common, combining the strengths of different simulation techniques for comprehensive analysis. For example, a 3D split Hopkinson pressure bar (3D-SHPB) numerical model was developed through the integration of PFC3D and FLAC3D techniques (Zhou et al., 2024).
Lessons Learned from Recent Longwall Mine-By Cases with Uncemented Casings
Authors: Zhang P. , Su D. , Tulu B. , Kim B. H. 
Published: August 2024

ABSTRACT:
Over 2,000 shale gas wells have been drilled in the longwall reserves of the Pittsburgh Coal Seam. When gas wells are in the vicinity of longwall mining, casing deformations are likely to occur due to longwall-induced subsurface movements and abutment stresses. One way to prevent casing deformation is to use a cementing alternative by leaving production casing uncemented. This paper presents three mine-by cases in which shale gas wells were in the chain pillars and the production casings were uncemented. These cases represent mine-by scenarios under shallow, medium, and deep cover. Casing deformations were measured with multi-finger caliper survey and predicted with numerical modeling. These mine-by case studies provide a general demonstration of how uncemented casing can uncouple production casing from longwall-induced stresses and deformations. Based on measurements of casing deformations and numerical modeling, the factors mentioned above are further analyzed to indicate in what conditions a cementing alternative may not eliminate production casing deformations. The knowledge gained from the mine-by case studies would help longwall operators and gas companies to optimize pillar design and casing design, thus minimizing the influence of longwall mining in the stability of shale gas wells in longwall pillars.

1. INTRODUCTION
With the shale gas boom, about 2,000 shale gas wells have been drilled through the current and future Pittsburgh coal reserves over the past 20 years. These shale gas wells, if located in longwall pillars, will be influenced by longwall mining. Longwall-induced subsurface ground movements would induce deformations in gas well casings. The concern is that if casing deformation is excessive, a casing breach could occur, and high-pressure shale gas could leak into the longwall mine with serious results. Because of the safety concern of gas wells in longwall pillars, the National Institute for Occupational Safety and Health (NIOSH) has been conducting research since 2016 to evaluate the effects of longwall mining on casing deformations under various mining depths and geological conditions.
NIOSH research has found that casing deformations are mainly caused by subsurface horizontal movements, especially under shallow and medium cover. NIOSH researchers have done several case studies with test wells in chain pillars under different overburden depths [Su (2016, 2017), Su et al. (2018, 2019), Zhang and Su (2021), and Zhang et al. (2022)]. These studies showed that longwall-induced relative horizontal displacements occur at weak-to-strong rock interfaces and are higher under shallow cover than under deep cover. The studies also showed that longwall-induced horizontal displacements are also affected by surface topography and strata dip.
Hydraulic Crack Propagation and Rock Permeability Under Osmotic Pressure Gradients with Implications for Deep CO2 Sequestration and Fraccing
Authors: Bažant Zdenek P. , Nguyen Anh Tay , Xu Houlin , Asem Pouyan , Labuz Joseph F. 
Published: August 2024

ABSTRACT:
Long-term deep sequestration of CO2-rich brine in deep formations of ultramafic rock (e.g. Oman serpentinized harzburgite) will be feasible only if a network of hydraulic cracks could be produced and made to grow for years and decades. Fraccing of gas- or oil-bearing shales has a similar objective. The following points are planned to be made in the presentation in Golden. 1) A branching of fracture can be analyzed only if the fracture is modeled by a band with triaxial tensorial damage, for which the new smooth Lagrangian crack band model is effective. 2) To achieve a progressive growth of the fracture network one will need to manipulate the osmotic pressure gradients by changing alkali metal ion concentration in pore fluid. 3) A standardized experimental framework to measure rock permeability at various ion concentrations and various osmotic pressure gradients is needed, and will be presented.

1 INTRODUCTION
Carbon dioxide (CO2) emissions by human activities is the largest contributor to global warming; therefore, effective carbon sequestration technologies attract great amount of interest. One emerging and promising technology for storing CO2 in the subsurface permanently is through carbon mineralization in mafic and ultramafic rock (Kelemen and Matter, 2008). Despite the abundance of these types of rock in the Earth's upper crust (Matter et al., 2016), the rate of this process in nature is too slow to reduce CO2 emissions effectively (Seifritz, 1990). One of the key challenges to achieve a sustainable and large-scale storage of CO2 by mineralization is to engineer a progressive growth of a fracture network conveying water with dissolved CO2 to reach a gradually increasing volume of the mafic rock formation. The CO2 rich water often cannot penetrate the tight matrix of silica-rich serpentinized harzburgites because under high concentrations of CO2, the wetting angle of CO2 -bearing water-rock-rock interface exceeds the critical value of 60 degrees. Therefore, the presence of a family of cracks is the only means by which CO2 -bearing fluids can interact with matrix of ultramafic rock (Bruce Watson and Brenan, 1987). Lateral fracture branching from a major fracture provides a sustainable fluid pathway and therefore is essential for continued rock-water geochemical reactions that lead to mineralization of carbonate minerals. Realistic computational modeling of hydraulic fractures in peridotite or basalt must involve lateral fracture branching and account for stress distribution changes between solid and fluid phases under constant tectonic stress, triggered by pore exposure to fluid pressure in hydraulic cracks.
Evolution of the Reservoir Stress Path During Depletion and Re-Inflation and its Implications
Authors: Seth P. , Mikulencak D. , Hofmann R. , Dudley J. W. 
Published: August 2024

ABSTRACT:
Several researchers have studied the impact of reservoir depletion on rock mechanical behavior and associated changes in in-situ stresses and reservoir depletion stress path. However, the evolution of the reservoir stress path (ratio of change in minimum horizontal stress with reservoir pressure change) due to re-inflation of the reservoir during injection operations such as waterflooding is less understood.
In this work, a more fundamental approach to the evolution of the reservoir stress path under both depletion and re-inflation is studied through core plug uniaxial-strain experiments and field-scale numerical modeling which includes the impact of plastic deformation. Both unconsolidated and consolidated sandstones are considered. Results from the uniaxial-strain compaction experiments agree with findings from 3-D field scale numerical modeling that the injection stress path coefficient γh,i = Δσh/ΔPinj is either similar or greater than the depletion stress path coefficient γh,d = Δσh/ΔPdep.
The findings in this study have significant implications for waterflooding operations, infill drilling window estimation for re-inflated reservoirs, and CO2 capture and storage operations (CCS). The assumptions on γh,i directly impact the allowable injection pressure, injection rate, and storage capacity for CCS projects. Hence a more thorough understanding could prevent overly conservative designs and promote a more accurate screening of potential waterflooding, infill drilling, and CCS projects.

1. INTRODUCTION
The reservoir minimum horizontal stress path is the ratio of change in total minimum horizontal stress, Δσh to change in reservoir pressure, ΔP:
(equation)
It is crucial to understand the anticipated minimum horizontal stress changes in a reservoir during long-term production and during injection operations such as waterflooding because σh is closely related to hydraulic fracturing in a normal stress environment. When describing the reduction in σh from depletion, the stress path coefficient is defined as γh,d. When describing the increase in σh from re-inflation, the stress path coefficient is defined as γh,i. The Δ's in these definitions are defined to always give positive values of γh,d or γh,i. The assumptions on γh,i (injection stress path coefficient) could impact the allowable injection pressure, injection rate, and storage capacity for waterflooding & CCS projects and a more thorough understanding could prevent overly conservative designs.