Polycrystalline diamond compact (PDC) cutters are used in geothermal energy drilling operations as they are exceptionally effective due to their strength and resistance to abrasion. It is important to understand the effect of downhole conditions to accurately model rock-cutter-rock interactions, as well as wear on the bit and drilling efficiency. Cutting efficiency is determined through the weight on the bit, rotational speeds, and other cutter and rock parameters in drilling, here we can comment on cutting efficiency through the cutting force. The ultimate goal of this research is to numerically model the PDC cutter–rock interaction in 3-D to find an optimal arrangement of parameters for efficient geothermal drilling. Using the combined finite discrete element method (FDEM), we model rock fracture and fragmentation for a single PDC cutter for both atmospheric and realistic well pressure conditions. We present the numerical analysis progression of PDC cutter-rock interaction in 2-D and 3-D for a range of cutting speeds, depth of cuts, and pressures using sandstone and granite as our rock materials. These parameters are varied to understand the optimal configuration to increase drilling performance as determined by cutting force, damage style, and fracture energy. Our models successfully reproduce laboratory values, which increases our understanding of rock fracture at downhole conditions.

The safety and durability of Class VI wells are critical for geological carbon sequestration (GCS). However, current GCS operations face unique challenges: unlike traditional Class II wells, Class VI CO2 injection wells operate at rates up to 100 times higher, dramatically increasing the risk of wellbore leakage and structural compromise due to severe temperature drops and associated mechanical stresses. Despite existing guidelines on material selection, there remains a substantial gap in understanding how rapid CO2 injection rates, low surface temperatures, and variable reservoir conditions interact to threaten long-term well integrity. This study presents a comprehensive, original workflow integrating advanced analytical and numerical models for both well flow and well integrity analysis. By systematically simulating a wide range of field-relevant scenarios—including variations in injection rate, CO2 temperature, and reservoir pressure—this work provides the first cross-validated assessment of cooling effects on wellbore. The results reveal that extreme temperature drops, up to 60 °C, can occur under high injection rates, particularly in depleted reservoirs, significantly increasing the risk of cement failure. Building on these insights, the study proposes innovative, practical well design and operational strategies, including ductile cement formulations, pre-stressing techniques, advanced insulation coatings, and proactive management of injection rates. The safety of Class VI well extends beyond simply using CO2 resistant materials. Cement materials should possess optimal thermo-hydraulic-mechanical-chemical properties for effective performance. This work provides a scientific basis for optimizing Class VI well designs, with direct benefits for minimizing environmental risk, lowering operational costs, and enhancing the long-term reliability of GCS.

Superhot geothermal wells represent one of the most technically demanding frontiers in the energy transition, offering immense potential for zero-carbon baseload power. However, the extreme thermal and multiphase conditions encountered, especially under lost circulation and fluid flashing, present significant risks to wellbore integrity. This study develops an advanced simulation framework that couples transient multiphase thermal modeling with a fully coupled thermoporoelastic stress analysis to evaluate well integrity in superhot geothermal environments. Using a representative geometry of the IDDP-2 well in Iceland, we simulate a wide matrix of injection scenarios, including no-loss, partial, severe, and total loss conditions with varying pump rates and ramp durations. Results show that total fluid loss and rapid injection can induce severe thermal shocks, particularly around casing shoe, where casing temperatures drop from 320 °C to 115 °C. These thermal gradients reduce bottomhole pressure due to diminished hydrostatic head and initiate high tensile and compressive stresses in the casing–cement–formation system. Model predictions are validated against temperature logs from the IDDP-2 injection test and show good agreement. To evaluate structural resilience under these conditions, detailed cement integrity analysis was performed. The results show that the thermal perturbation experienced by the cement sheath depends not only on the final temperature but also on the cement setting temperature and its initial stress state. For example, assuming a cement setting temperature of 150 °C, the combined thermal variation may range from –35 °C to +170 °C. The analysis demonstrates that without pre-stress, the cement sheath is vulnerable to failure across a narrow operational window. In contrast, with a favorable initial stress state (e.g., 10 MPa), the safe temperature variation range expands significantly to –90 °C to +250 °C. The findings underscore the need for high-resolution thermal modeling and integrated stress assessment in geothermal well design and highlight operational strategies to mitigate thermal integrity risks in future superhot developments.

Fracturing is a fundamental physics phenomena with broad relevance across multiple domains, ranging from infrastructure integrity, aerospace durability, reservoir production, and seismic events. We present a diverse dataset of simulated fracture evolution and material failure generated from two numerical solvers: the phase-field method and the combined finite-discrete element method (FDEM). These solvers differ in formulation, physical fidelity, and computational efficiency. The dataset includes five materials: PBX, anisotropic shale, tungsten, aluminum, and steel. For each, phase-field simulations span 400,000 cases: 200,000 under uniaxial tension and 200,000 under biaxial tension. The computationally expensive FDEM simulations include 90,000 split evenly among PBX, shale, and tungsten under uniaxial loading. All simulations begin with randomized initial fracture patterns. Each entry includes temporal data capturing fracture propagation dynamics. This comprehensive dataset is designed to support the development of foundational or surrogate machine learning approaches for predicting material failure. While no such models are introduced here, the dataset lays a robust foundation for advancing future research and innovation in these areas.

Numerical modeling of explosion crater formation requires accounting for complex physical processes. Numerical validation of explosion cratering is an important step in modeling and requires experimental data for comparison. Models using discrete elements and continuum models have both benefits and drawbacks to their approaches. In this work, we consider both an arbitrary Lagrangian-Eulerian (ALE) hydrocode and a finite discrete element method (FDEM) approach to modeling the formation of the Sedan crater, the largest human-made crater in the United States. The Sedan crater formed from an underground nuclear detonation in the Nevada desert as part of Project Plowshare. Our models show that the continuum approach of the hydrocode matched well compared to early test time prior to the mound rupture and subsequent fireball venting, when most of the alluvium exhibited fluid behavior. Our FDEM approach matched the final crater dimensions well, after material had settled back into the crater, when material strength and solid mechanics play key roles. Our work shows how leveraging the benefits of multiple numerical approaches can lead to better understanding of complex physical problems, especially problems with limited experimental data. By using a continuum approach to early-time hydrodynamics and an FDEM approach to later-time solid mechanics, we can better understand the different physical regimes of explosion crater formation.

We provide a suite of verification examples for coupled thermo-hydro-mechanical (THM) processes in subsurface flow. The considered scenarios are subsets of THM problems with and without fractures. The examples include classical problems presented by Terzaghi, Schiffman, Mandel, Wijesinghe, McNamee and Gibson, Noda and Lauwerier. For each example, we provide a description of the physical problem setup, the governing equations, the solution to the equation, and comparison of that solution with a new THM simulator. Python scripts for the solutions are available in a Git repository for other modeling groups to verify their own THM simulators. We demonstrate this new verified simulator’s full THM capabilities by modeling a hypothetical enhanced geothermal system to show how dynamically modifying fracture aperture impacts energy production over a period of ten years.

Accurately predicting when and how materials fail is critical to designing safe, reliable structures, mechanical systems, and engineered components that operate under stress. Yet, fracture behavior remains difficult to model across the diversity of materials, geometries, and loading conditions in real-world applications. While machine learning (ML) methods show promise, most models are trained on narrow datasets, lack robustness, and struggle to generalize. Meanwhile, physics-based simulators offer high-fidelity predictions but are fragmented across specialized methods and require substantial high-performance computing resources to explore the input space. To address these limitations, we present a data-driven foundation model for fracture prediction, a transformer-based architecture that operates across simulators, a wide range of materials (including plastic-bonded explosives, steel, aluminum, shale, and tungsten), and diverse loading conditions. The model supports both structured and unstructured meshes, combining them with large language model embeddings of textual input decks specifying material properties, boundary conditions, and solver settings. This multimodal input design enables flexible adaptation across simulation scenarios without changes to the model architecture. The trained model can be fine-tuned with minimal data on diverse downstream tasks, including time-to-failure estimation, modeling fracture evolution, and adapting to combined finite-discrete element method simulations. It also generalizes to unseen materials such as titanium and concrete, requiring as few as a single sample, dramatically reducing data needs compared to standard ML. Our results show that fracture prediction can be unified under a single model architecture, offering a scalable, extensible alternative to simulator-specific workflows.

ABSTRACT: The coupling and interactions among rock deformation, fluid flow, heat transfer and geochemical reactions has become an essential topic in complex subsurface systems for geothermal energy production. To improve the understanding and minimize the uncertainty in subsurface geothermal energy production operations, a new coupled Thermo-Hydro-Mechanical-Chemical (THMC) framework has been developed at Los Alamos National Laboratory (LANL) since 2020. Three LANL-developed codes: HOSS, Amanzi, and dfnWorks are integrated in the LANL-developed InyanCC THMC coupling framework. The InyanCC THMC framework has been well verified against selected benchmarking problems and the simulation results show good agreement with analytical solutions. Furthermore, the InyanCC framework is used to simulate a fully-coupled Thermal-Hydro-Mechanical problem in a stylized subsurface enhanced geothermal system to investigate the effects of fracture aperture change on the energy production rate. The simulation results represent the cooling down progress of the rock matrix and fractures, demonstrating the capability of InyanCC in simulating THM coupling problems in the field for Enhanced Geothermal Systems. The comparison of heat propagation velocity between changing aperture and fixed aperture simulation further emphasizes the significance of fracture aperture change on the heat transfer in the EGS. 1. INTRODUCTION As one of the clean renewable and sustainable energy resources, geothermal energy has been widely applied for electricity generation, heating, and cooling in many countries. Department of Energy's GeoVision Study and EarthShot Initiative has outlined that the breakthroughs in enhanced geothermal system (EGS) technologies could unlock over 100 GW of clean power in the US (DOE 2019; Augustine et al. 2022). Geothermal energy is often produced by circulating water through a high temperature reservoir where the fractures and joints inside the reservoir play a key role by introducing the dominant flow paths. Pandey et al. (2015) found that the dynamic change of fracture aperture will greatly affect the production temperature. A variety of studies in the past have pointed out that heat extraction rates are very sensitive to fracture spacing (Fox et al. 2013; Ekneligoda and Min Ki-Bok 2014) and fracture geometries (Andrade et al., 2004).

The Hybrid Optimization Software Suite (HOSS), which combines the finite -discrete element method (FDEM), is an advanced approach for simulating high-fidelity fracture and fragmentation processes. However, the application of pure HOSS simulation is computationally expensive. Meanwhile, machine learning methods, which have shown tremendous success in various scientific problems, are increasingly being considered as promising alternatives to physics -based models in scientific domains. Thus, the objective of this work is to develop a new data -driven methodology to accurately reconstruct micro -crack fractures in both spatial and temporal fields. We leverage physical constraints to regularize the fracture propagation in long-term reconstructions. Additionally, we introduce perceptual loss and several machine learning optimization approaches to further enhance the reconstruction performance of fracture data. We demonstrate the effectiveness of the proposed method through both extrapolation and interpolation experiments. The results confirm that the proposed method can reconstruct high-fidelity fracture data across space and time in terms of pixel -wise reconstruction error and structural similarity. Visual comparisons also yield promising results in long-term reconstruction.

Simulations of rock damage and gas transport following underground explosions that omit preexisting fracture networks in the subsurface cannot fully characterize the influence of geo-structural variability on gas transport. Previous studies do not consider the impact that fracture network structure and variability have on gas seepage. In this study, we develop a sequentially coupled, axi-symmetric model to look at the damage pattern and resulting gas breakthrough curves following an underground explosion given different fracture network realizations. We simulate 0.327 and 0.164 kT chemical explosives with burial depths of 100 m for 90 stochastically generated fracture networks. Gases quickly reach the surface in 30% of the higher yield simulations and 5% of the lower yield simulations. The fast breakthrough can be attributed to the formation of connected pathways between fractures to the surface. The formation of a connected damage pathway to the surface is not clearly correlated with the fracture intensity (P32) in our simulations. Breakthrough curves with slower transport are highly variable depending on the fracture network sample. The variability in the breakthrough behavior indicates that ignoring the influence of fracture networks on rock damage, which strongly influences the hydraulic properties following an underground explosion, will likely lead to a large underestimation of the uncertainty in the gas transport to the surface. This work highlights the need for incorporation of fracture networks into models for accurately predicting gas seepage following underground explosions.

In recent decades a whole new research discipline dealing with physics of discontinua has emerged. Unlike continuum, discontinuum builds a picture of the world where a large number of independent agents interact with each other in order to produce virtual emergent phenomena that closely match real world emergent phenomena. The discontinuum assumption complements the continuum assumption and both assumptions often work together in what is termed hybrid continuum-discontinuum formulations. In this chapter some key simulation tools of Computational Physics of Discontinua are introduced, while hybrid continuum-discontinuum simulation approaches and the combined finite-discrete element method (FDEM) are described in some detail. In this context, the concept of virtual experimentation and its extensions towards AI (artificial intelligence) based scientific discovery, together with accompanying custom-made hardware architectures, are introduced and explained.

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.

ABSTRACT: Simulating the structural response of concrete and reinforced concrete structures to blast loading conditions is a challenging task, as it requires modeling the fracture and fragmentation processes in this composite material with reasonable computational efficiency for large scale simulations. To address this problem, novel shell formulations have been incorporated within Los Alamos National Laboratory's implementation of the combined finite-discrete element method, called HOSS (Hybrid Optimization Software Suite). In this numerical study, these new finite element formulations are utilized for modeling thin concrete and metal linings for applications in building construction. Both unreinforced and reinforced concrete can be modeled with this method which opens the door for addressing many practical applications. 1. INTRODUCTION Since its inception, the combined finite discrete element method (FDEM) has become a tool of choice to address a variety of problems involving fracture and fragmentation processes in solids. FDEM combines the strengths of the finite element method (FEM) and the discrete element method (DEM). The key advantage of FDEM is the utilization of finite strain-based deformability combined with suitable constitutive material laws which are then merged with discrete element based transient dynamics, contact detection, contact interaction solutions, and objective discrete crack initiation and crack propagation solutions (Munjiza, 2004). The comparison of DEM and FEM with a schematic visualization of FDEM is shown in Fig. 1. In FDEM, the solid bodies are modeled as a collection of deformable particles that are bonded with each other (Rougier et al., 2014), Fig. 1. These solid bodies (called discrete elements) are discretized into finite elements where their finite displacements and rotations are assumed a priori (Munjiza, 2004; Munjiza et al., 2011, 2015). The bonding is numerically represented with cohesion points along the boundaries of the deformable particles (Rougier et al., 2014). The cohesion of these bonds is a combination of normal cohesion and tangential cohesion. When an FDEM model experiences fracture, failure, or fragmentation and the material is exposed to high enough levels of stress, these bonds become increasingly strained until they reach their ultimate strengths and eventually break resulting in the adjacent finite elements to also become unbonded (Rougier et al., 2014). The single discrete element domains are transformed into interacting domains upon which discretized contact solutions can be used for both contact detection and contact interaction (Knight et al., 2020).

SUMMARY Meteorite impacts have proved to be a significant source of seismic signal on the Moon, and have now been recorded on Mars by InSight seismometers. Understanding how impacts produce seismic signal is key to the interpretation of this unique data, and to improve their identification in continuous seismic records. Here, we use the seismic Representation Theorem, and particularly the stress glut theory, to model the seismic motion resulting from impact cratering. The source is described by equivalent forces, some resulting from the impactor momentum transfer, and others from the stress glut, which represents the mechanical effect of plasticity and non linear processes in the source region. We condense these equivalent forces into a point-source with a time-varying single force and nine-component moment tensor. This analytical representation bridges the gap between the complex dynamics of crater formation, and the linear point-source representation classically used in seismology. Using the multiphysics modelling software HOSS, we develop a method to compute the stress glut of an impact, and the associated point-source from hypervelocity impact simulations. For a vertical and an oblique impact at 1000 m s−1, we show that the moment tensor presents a significant deviatoric component. Hence, the source is not an ideal isotropic explosion contrary to previous assumptions, and draws closer to a double couple for the oblique impact. The contribution of the point force to the seismic signal appears negligible. We verify this model by comparing two signals: (1) HOSS is coupled to SPECFEM3D to propagate the near-source signal elastically to remote seismic stations; (2) the point-source model derived from the stress-glut theory is used to generate displacements at the same distance. The comparison shows that the point-source model is accurately simulating the low-frequency impact seismic waveform, and its seismic moment is in trend with Lunar and Martian impact data. High-frequencies discrepancies exist, which are partly related to finite-source effects, but might be further explained by the difference in mathematical framework between classical seismology and HOSS’ numerical modelling.

Continuum mechanics has been one of the major branches of physics where theoretical developments such as theory of elasticity, theory of plasticity, fluid mechanics, and solid mechanics are mostly based on differential equations; these were developed during the second half of the nineteenth century and the first half of the twentieth century. In the second half of the twentieth century computational physics and computational mechanics of continuum were developed to such an extent that now modern science, engineering and technology cannot be imagined without computer simulations. In recent decades, a complementary approach based on discontinuum has been employed and the fields of computational physics of discontinua and computational mechanics of discontinua are mainstream analysis approaches. In this article the state-of-the-art of this modern simulation technology is summarized along with the key computational methods, i.e., molecular dynamics, discrete elements, and the combined finite-discrete element methods.

ABSTRACT The complex coupling interaction phenomena among rock mechanics, fluid flow, heat transfer and geochemical reactions has become a critical topic in complex subsurface systems including the production of unconventional oil and gas. In this paper, we introduce a fully coupled Thermo-Hydro-Mechanical-Chemical (THMC) framework that is being developed at Los Alamos National Laboratory (LANL). The framework integrates four LANL-developed codes: HOSS, Amanzi, dfnWorks and InyanCC. HOSS simulates deformation of the rock matrix as well as the opening, closing and shear sliding in the discrete fractures (mechanics), while Amanzi solves subsurface multiphase flow and reactive transport, dfnWorks generates meshes with complex discrete fracture networks, and InyanCC links the mechanics and flow solvers while controlling the whole simulation processes. The advantages of this coupling framework are: 1) it is based on hybrid continuum-discontinuum approaches which overcomes the limitations seen with pure continuum assumptions; 2) both mechanics and subsurface flow solvers are fully parallelized for distributed memory systems which allows the users to simulate large scale problems on HPC clusters. Different selected benchmarking problems are simulated using this THMC framework. The results show good agreement with the analytical solutions, which verifies the accuracy of the framework. INTRODUCTION Current applications of geotechnical engineering and geo-energy in the subsurface rely significantly on complex coupling process among rock mechanics, fluid flow, heat transfer and geochemical reactions, including geothermal production, unconventional oil and gas production and underground nuclear explosions. Hence, Modeling Thermo-Hydro-Mechanical-Chemical (THMC) processes is essential in understanding the coupled processes in subsurface geological media. Fully addressing the computational challenge of coupled THMC process simulation has been exacerbated by the inability to simulate coupled processes in both the rock matrix and discrete fractures. However, modern subsurface simulators taking advantage of the high-performance computation have been proposed to overcome these challenging problems. Cheng, 2016; Rutqvist et al., 2001; and Wang, 2000 proposed different approaches for modeling the evolution of pressure, stress, and temperature fields in porous media, including equations for pressure diffusion, mechanical equilibrium, and energy transport. Rutqvist and Stephansson (2003) introduced a coupled THM model based on sub-grid scale fracture networks. Min and Jing (2003) reported numerical simulations of hydro-mechanical coupling in fracture networks. These models capture the contribution of discrete fracture deformation to permeability anisotropy through the effective properties such as permeability and porosity. However, these methods have limitation in modeling time-evolving large scale THM system when the characteristic length of network structures is much larger than the grid block scale.

ABSTRACT Three-point bending test is a widely used laboratory test for the estimation of the flexural force-displacement response of the material. It is well known that the results of the three-point bending test are sensitive to the specimen and the loading. In this work, the impact of the boundary effects on a single notch three-point bending test is studied using LANL's combined finite-discrete element method (FDEM) based code, the Hybrid Optimization Software Suite (HOSS). To this goal, a series of virtual experiments with different specimens and boundary conditions are conducted. The influence of the notch location, and fixture shape are studied. Results clearly show that these boundary conditions greatly influence on the fracture initiation and propagation behaviors as well as the flexural force-displacement response. INTRODUCTION Three-point bending test is a long-used technique applied mainly in the oil and gas industry to estimate the fracture toughness of rocks in the laboratory. In this test, the vertical tension is applied to the convex side of a sheet or plate specimen placed on two supporting fixtures with a set distance apart. A variety of numerical approached have been proposed to analyze the crack initiation and growth behavior of three-point bending test in the past several decades (Fakhimi, 2005; Kokot, G., Binkowski, 2011; Ramos, 2015; Klasztorny, 2018: Sauvage, 2020). However, the effect of boundary conditions is still lacking consideration in the previous studies. Motivated by the prior works and the knowledge gaps remaining in effect of boundary conditions, a finite-discrete element method (FDEM) model is applied here to interpret three-point bending experiment results in order to characterize dependence of rock fracture behavior on boundary conditions and notch location. The present study therefore aims to capture the crack initiation and propagation behavior for laboratory experiments using material properties and traction-separation law that has been calibrated by comparing the simulation results with lab experiments provided by Jiang et al. (2021) and Jiang et al. (2022), regardless of notch location. This study aims to revisit the effect of boundary conditions on crack initiation and growth behavior under three-point bending test. For this purpose, a 2D plane-strain model is developed using HOSS, a combined finite-discrete element method (FDEM) based code. Different boundary conditions and notch locations are considered for lab-scale simulations. Indeed, simulation results indicated that the crack initiation location and crack growth behavior can vary with different boundary conditions and notch locations, which can challenge the general belief that the crack initiation and propagation behavior should not be affected by the boundary conditions greatly.

•Hydraulic fractures can branch in subsurface reservoirs with anisotropic horizontal stresses when natural, permeable weak layers exist.•Anisotropic Biot stress coefficient and its changes in weak layers during fluid pressurization provide a mechanism for fracture branching.•Prediction of complex fracture structures in the subsurface requires a three-dimensional hydro-mechanical coupled model.