bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Study of Rock Breakage Under Extreme Submerged Confining Pressure: Can DTH Hammer Drilling Deliver?
Authors: Gerbaud L. , Velmurugan N. , Aising J. , Chambres C. , Naderi S. , Latham J. P. , Xiang J. , Yang X. 
Published: August 2024

ABSTRACT:
Drilling cost is one of the main obstacles hindering the development of deep geothermal energy, especially in hard granite formations at great depths. In ORCHYD, an H2020 project, we develop an innovative drilling technology that merges percussion drilling and high-pressure water jetting for drilling hard crystalline rocks. In laboratory, we have demonstrated a fourfold improvement in drilling performance when contrasted with conventional techniques. This article delves into the study of impact of realistic operational conditions, characterized by high in-situ confining stress and hydrostatic pressure, on the drilling technique.
We study variables affecting the mud hammer's performance. Experimentally, our drilling test laboratory houses a set-up designed to dissect the mechanisms of rock fracture during indentation under realistic downhole conditions. Numerically we harnessed our in-house rock fracture software, SOLDITY that leverages a hybrid FDEM method to simulate the intricate interactions of rocks under confining pressures.
Our analysis of experimental and numerical data centered on rock fractures. Our findings show that breaking rock can be 2-3 times more challenging under higher confinement compared to lower confinement conditions. This insight has significant implications for optimizing ORCHYD techniques, improving the efficiency of rock destruction.

1. INTRODUCTION
Geothermal energy is positioned as one important component in the drive to achieve Net Zero Emissions (NZE) by 2050, offering a clean, sustainable, and reliable source of renewable energy. Nevertheless, the high costs associated with geothermal drilling pose a significant obstacle to its widespread adoption and scalability (Angelone, 2014). The primary cost driver in deep geothermal drilling stems from the necessity to penetrate deep and dense crystalline rock formations, such as granites, typically located at depths exceeding 4 km. Deeper drilling not only escalates operational expenses but also demands a substantial increase in the energy required to break rocks under extreme confining stresses and hydrodynamic pressures.
Conventional rotary drilling, such as roller cone and polycrystalline diamond carbide (PDC) bits, encounter difficulties penetrating hard formations like granite, resulting in sluggish rate of penetration (ROP) (Cardoe et al., 2021; Baujard et al., 2017). Percussion drilling, characterized by its effectiveness in penetrating hard formations, has garnered considerable attention in deep geothermal industry, specifically for basement drilling. Despite its advantages, such as enhanced rock penetration and reduced drilling costs, percussion drilling encounters limitations, notably in achieving higher ROP under high confining conditions dictated by geological stresses and mud pressure in the wellbore (Gnirk and Cheatham, 1965; Han et al., 2006).
Understanding Cement Hydration in CO2 Reservoirs: Geochemical Modeling in the Powder River Basin
Authors: Allam L. , Malki M. L. , Mellal I. , Kolla N. , Rasouli V. , Dehdouh A. , Abdelhamid C. 
Published: August 2024

ABSTRACT:
The Powder River Basin is one of the primary hydrocarbon-bearing basins in the state of Wyoming. This provides consequential knowledge on the basin's characteristics, which allows effective identification of potential candidates for CO2 storage. In this paper, we aim to characterize the hydration of Portland cement in CO2 injection wells. Properties of the Minnelusa formation in the Powder River Basin serve as a base case scenario. From this, we will run a sensitivity analysis to determine the influence of various parameters on cement hydration. These parameters consist of pressure, temperature, formation water fraction, and water-to-cement ratios. The findings will allow us to determine the most influential parameters affecting cement hydration, hence threatening the integrity of CCUS operations. For this purpose, we used the geochemistry modeling software PHREEQC. The CEMDATA thermodynamic databases were used to supplement the default PHREEQC database with missing mineral phases involved in cement hydration. For our simulations, initial data include formation water compositions, formation mineral fractions, clinker phases fractions and downhole conditions. The thermodynamic process of solids precipitation was then simulated for each of the base cases, then at various conditions. The obtained simulation results include phase assemblage at equilibrium for each case. From a well integrity perspective, predicted phase assemblage of the cement sheath allows for tailored cement degradation analysis on a well-to-well basis when activated by carbonic acid. In addition, the phase assemblage can be used in combination with time-dependent diffusivity and convection models for higher precision characterization.

1. INTRODUCTION
The global imperative to address climate change has intensified the focus on carbon capture and storage (CCUS) technologies, particularly in the context of ensuring the integrity of CO2 storage injection wells (IPCC, 2005). As the world grapples with the urgent need to reduce greenhouse gas emissions, CCUS has emerged as a key strategy to mitigate climate change (IPCC, 2005). The reliability and safety of CO2 injection wells are central considerations, with challenges ranging from corrosion to cement degradation and scale formation that can compromise the effectiveness of CCUS initiatives (Bai et al., 2016; Carroll et al., 2016). Therefore, having a proper understanding of the evolution of well integrity components offers means of preemptive maintenance (Le Guen et al., 2008).
Thembelani and Khuseleka Mines in the Bushveld Igneous Complex's Western Limb in South Africa
Authors: Masethe R. , Durapraj S. , Modika M. , Ngwenya M. , Adoko A. , Zvarivadza T. 
Published: August 2024

ABSTRACT:
The Merensky (MER) orebody in the Bushveld Complex in South Africa has been mined extensively. Regional and local pillars, zones of unmined ground, potholes, and remnants were left in-situ. 15 to 400 m beneath the MER orebody, the UG2 chromitite orebody is currently being exploited. Due to the location of these two orebodies, it is postulated that the unmined ground in the MER above may have an influence on the current UG2 ground conditions. Although many mining variables could have impacted the successful exploitation of the UG2, the in-situ blocks of ground on the MER reef horizon seemed to present an additional risk, which had not been extensively researched before. Of concern is that, this phenomenon is occurring at different depths and different middling between the two orebody packages. In some cases, it was found that relatively shallow UG2 reef mining could encounter conditions like those experienced in deep mining environments (e.g., spalling, scaling pillars, and rockburst hazard). Source mechanisms of significant mining-related seismic events (ML≥1.0) were analyzed and facilitated the comprehension of the dominant modes of failure. Much of the work focused on seismic events triggered by movement along planes of weakness and the closure rate experienced by the stopes in both the MER and UG2.

1. BACKGROUND
The Merensky Reef is a regular, persistent tabular orebody with various layers: pegmatoid, chromitite, and pyroxenite (Lougher and Mellowship, 1991). It is generally composed of an upper feldspathic pyroxenite assemblage near the top of the Upper Group of the Upper Critical Zone of the Bushveld Complex. It is overlying a thin basal chromitite stringer, followed by an anorthosite to norite footwall and a thin anorthosite layer (0.1 – 0.2 m thick), which is underlain by norite (Fig. 1). Locally, this is termed a "pyroxenite reef".
The UG2 chromitite layer comprises chromitite and pegmatoid units. It is well renowned for its short-distance undulation due to its conformable interaction with the footwall. The UG2 Reef is made up of a coarse plagioclase-orthopyroxene pegmatoid layer that can grade into coarse pyroxenite (Leeb-Du Toit, 1986). The reef's thickness ranges from 0.2 to 2 m, with an average of about 0.7 m. The absence of coarse pyroxenite beneath the UG2 chromitite layer suggests that the stratum is potholed (Lougher and Mellowship, 1991). The UG2 Reef consists of a primary chromitite layer, which contains the majority of the PGM and base metal mineralization, followed by a poorly mineralized pegmatoidal pyroxenite footwall (Fig. 1). The hanging wall to the main chromitite layer is feldspathic pyroxenite with up to four thin, weakly mineralized chromitite layers.
New Method of XRF/XRD Based Mineralogy for Estimating Matrix-Modulus, Biot's-Coefficient and Effective-Stress Using VRH and HS Bounds of Rock Physics Principles
Authors: Prasad Umesh , Alarcon P. Nora , Franquet Javier 
Published: August 2024

ABSTRACT:
The concept of ‘effective stress’ is the foundation of any subsurface investigations which controls the deformation, fracture, failure, and production decline characteristics including dynamic acoustic wave propagation or specifying confining pressures in laboratory testing. Effective stress (σ′) is the difference between total stress (σ) and existing pore pressure (Pp) multiplied by Biot's coefficient, α. The ‘α′ is expressed in terms of bulk modulus (Kb) and matrix bulk modulus (Kma) as in 1 − Kb/Kma. The Kb is estimated by acoustic logs as well as measured by triaxial test. However, Kma is difficult to measure, especially in low porosity or low permeable shale/caprock or crystalline rocks. Current advancement in hardware and software enabled use of portable X-ray fluorescence (XRF) and X-Ray diffraction (XRD) tools to get inorganic elements and successively mineralogy for estimating Kma and further constrain α using rock-physics models (VRH or HS) for better confidence in modeling and simulation.

1. INTRODUCTION
In any civil, mining, or petroleum application the concept of stress (or strain) under the influence of load or displacement is the foundation of geomechanical investigations. However, since the subsurface geological formation consists of pore, voids and fluid pressure, it is the ‘effective stress’ and not the ‘total stress’ which controls the deformation, fracture, failure, and production decline characteristics including dynamic acoustic wave propagation in rock formations.
Fig 1 shows the elastic behavior of volumetric strain change for dry and saturated sandstone under laboratory testing environment while changing the confining and pore pressure (Pp). While ignoring the Pp, change in elastic behavior is not explained, by using the concept of Terzaghi (1934) effective stress the response in elastic behavior is better explained. However, while incorporating the concept of Biot (1941), full elastic behavior is best explained [modified after Nur, 1971].
Effective stress is also useful in any triaxial core testing in the laboratory for calibrating log-based estimations. Effective stress (σ′) is expressed as difference between total stress (σ) applied and existing pore pressure (Pp) multiplied by Biot's coefficient, α as postulated by Terzaghi, (1934) and Biot (1941), Eq. (1). The ‘α′ for highly porous rocks is unity where load applied is counteracted equally by grain-matrix and pore-pressure. However, for low porosity and low permeable tight rocks as encountered in unconventional reservoirs, CCUS cap-rocks, or geothermal crystalline rocks, only a fraction of load is shared by pore fluid and the ‘α’ is much smaller than unity.
Reliability-Based Design (RBD) Updating by Sample Reweighting for Rock Slope Design
Authors: Aladejare A. E. , Idowu K. A. , Ozoji T. M. 
Published: August 2024

ABSTRACT:
Rock slope design comprises systematic evaluation of geological, geotechnical, and engineering parameters affecting safety and stability of slopes in rockmass. However, it is common to have several design possibilities for a single slope in rockmass. In the forementioned instance, reliability-based design (RBD) could provide insights on the most feasible slope design for rockmass. However, this generally involves several computational runs for each slope design. In this study, combined Monte Carlo simulation (MCS) and sample reweighting method was explored with the aim of obtaining parameters for rock slope design during a single computational run. With this approach, the repeated run of MCS for different design possibilities are avoided. One key advantage of the method is that it saves computational time by using a single run of simulation since there is possibility of a great number of design scenarios at a rock slope. To evaluate the performance of this approach, the proposed method was applied to a real-life rock slope. Results reveal that the proposed approach for rock slope design is both reliable and advantageous by providing sufficient failure samples for reliability estimation of the final designs for various design possibilities. In addition, the approach proposed in this study can link site characterization processes to design, and significantly reduces the time and efforts required for the processes. Through the proposed approach, there is improved knowledge on the contribution of uncertain rock parameters and slope conditions involved in design to the rock slope.

1. INTRODUCTION
Mining engineering is faced with several uncertainties, ranging from variability of rock conditions, uncertainties in rock parameters that are affected by geological processes, limited number of test values or site mapping, and model uncertainties (Baecher and Christian, 2003; Qi and Li, 2018; Aladejare and Wang, 2017). The uncertainties affect mining designs, and incorporating the uncertainties into mining design procedures in a quantitative manner is crucial to obtaining reliable designs of structures in mining engineering. A reliability-based framework can be used for such incorporation. In the past few decades, several studies have been conducted on reliability analysis of slope stability (Jimenez-Rodriguez et al. 2006; Hoek 2007; Tang et al., 2013; Dadashzadeh et al., 2017; Aladejare and Wang, 2018; Aladejare and Akeju, 2020).
Slope Stability Finite Element Modeling of El Misti Volcano, Peru
Authors: Hollander J. A. , Walton G. , Villeneuve M. , Salas G. , Luza C. 
Published: August 2024

ABSTRACT:
El Misti is a 5822 m elevation symmetrical, andesitic stratovolcano located near the city of Arequipa in Peru. Numerous historic debris and avalanche deposits indicate that the volcano slopes could be unstable, and that seismic or volcanogenic activity might have the potential to trigger movement that could threaten Arequipa. To evaluate this potential, a cross-section was first developed along a transect from the summit southwest towards Arequipa based on available geologic information. The stability of the southwestern slope of El Misti approaching Arequipa was then investigated using 2D finite element homogenized continuum modeling. The shear strength reduction (SSR) method was used to find critical strength reduction factors (SRF) at which the slope is marginally stable (SRF ∼ 1) given a pseudo-static seismic loading based on the peak ground acceleration (PGA) for Arequipa. Possible mechanisms of slope failure for different assigned subsurface conditions were investigated.

1. INTRODUCTION
El Misti is a 5820 m elevation composite stratovolcano with an extensive history of explosive eruptions, and lava and debris flows (Thouret et al., 2001). It is constructed of a composite of accumulated material from several sequences of eruptions and collapses. It lies to the northeast of the city of Arequipa, Peru. Arequipa has seen rapid growth in recent years, with a population of 1.38 million people per the 2017 national census, up from 700k in 1980 (CEIC, 2021).
Stratovolcanoes are built rapidly compared to non-volcanic mountains, leading to potentially unstable flanks and edifices (van Wyk de Vries and Francis, 1997). Collapse of these deposits can lead to large rock avalanches and debris flows with extensive runout lengths (Reid et al., 2000). Debris flow and collapse deposits can be seen in the historic geologic record of El Misti and pose a threat to the city of Arequipa and surrounding areas (Acocella, 2005; Thouret et al., 2001). Seismic activity, such as is common in the tectonic environment of Arequipa, or eruptions can trigger such massive collapses (Reid, 2004; Voight et al., 1983). Therefore, understanding the current stability of El Misti against seismic influences is vital to evaluating its long-term stability and the safety of residents of Arequipa.
Assessment of Leakage Risk of Legacy Wells Based on Wellbore Schematics Using a Systematic Approach
Authors: Anwar I. , Meng M. , Carey W. J. , Stauffer P. , Lackey G. 
Published: August 2024

ABSTRACT:
A systematic approach is used to assess the leakage risk of legacy wellbores using available wellbore information from a site in Louisiana, USA. The proposed approach assesses potential risk of groundwater contamination resulting from fluid leakage in legacy wells associated with carbon sequestration operation. The assessment incorporates several key factors, such as leakage through open borehole pathways, leakage through annular spaces between the casings, inadequate cement design, presence of fish in wellbore, and complex sidetracks. The approach integrates geological information with well construction data to form wellbore schematics, contributing to a richer understanding of 10 legacy wells located near a possible sequestration site. In addition, we have established a qualitative risk scoring system that prioritizes wellbores susceptible to CO2 leakage for remediation or leak identification/monitoring. From assessing the well features, accumulated qualitative risk scores are obtained. As per the current assessment described in this study, a combined risk score exceeding 20 for any legacy well within the area of review is indicative of a potential leakage risk.

1. INTRODUCTION
Wells, or wellbores are subsurface structures that are typically constructed of multiple steel casings surrounded by an oil-well cement or Portland cement sheath to create a seal in the annular space between the host formation and the steel casing or between the casings (Figure 1). Various categories of both documented and undocumented wells, including abandoned wells, orphaned wells, idle wells, and inactive wells, are found all over the world. For simplicity, we have termed all the above-mentioned wells as legacy wells in this article. A properly designed well can prevent leakage of fluid from an underground reservoir during operational phases, and if effectively plugged and abandoned, the integrity of the well can be maintained, thereby preventing upward leakage or movement of fluids between geologic layers for an extended period. However, the old legacy wells may have construction flaws, substandard workmanship, improper well abandonment, and much more, leading to a likely compromise in their integrity. In this article, we have used the terms "well" and "wellbore" interchangeably.
Failure Mechanisms in Jointed Rock Slopes Concerning the Dip Angle of Continuous Joints
Authors: Shandilaya Shivesh , Roshankhah Shahrzad 
Published: August 2024

ABSTRACT:
Jointed rock slopes surround critical infrastructure and communities, such as dams, roads, tunnels, bridges, mines, and buildings. The mechanical behavior of jointed rock masses depends on the complex interactions between joints, rock matrix, boundary conditions, and loading states. When a jointed rock mass undergoes environmental stressors, the generated tensile and shear cracks through intact rock blocks and pre-existing discontinuities determine the mechanisms and implications of the consequent slope failure. However, predicting fracture evolution, corresponding stress transfer mechanisms, and consequent failure states are challenging due to the complex interactions between the slopes' structural components. This study aims to understand the effects of such interactions on the overall response of slopes concerning the dip angle of continuous natural fractures when a local failure is triggered in fractures close to the slope face. This study employs the combined finite discrete element method (FDEM) to examine the slopes' mechanical response, including the progressive failure mechanisms. The results of this quantitative analysis are processed and visualized through graphical representations depicting the distinct failure modes observed in jointed rock slopes with various dip angles.

1 INTRODUCTION
Failure of rock slopes ranks among the most dangerous geological hazards, causing yearly fatalities, significant disruptions to infrastructure, environmental challenges, and adverse socioeconomic impacts. Thus, it is crucial to detect the early signs of failure by understanding the mechanisms that drive new fractures, activate pre-existing fractures, and finally cause a global failure. Failure of rock slopes occurs for various reasons that contribute to either an increase in shear stresses applied on the slope or a decrease in the shear strength of the rock mass. The latter may happen due to weathering, water infiltration, and anthropogenic activities. Studies show that the impact of shear strength reduction on the failure mechanism of jointed rock slopes depends on factors like joint or discrete fracture network (DFN) density (Wang et al., 2003), roughness (Ban et al., 2020, Rullière et al., 2020) and orientation of the joints (Bahaaddini et al.,2013), the properties of the infill material within the joints (Jiang et al., 2015), the degree of saturation of the infill (Indraratna et al., 2014), and the average normal stress acting on the joints (Mišcˇević et al., 2014). The arrangement of fractures within a rock mass can also determine the potential for block detachment, toppling, and sliding. Highly connected fracture networks can delineate potential sliding or toppling blocks, significantly influencing slope stability (Romer & Ferentinou, 2019).