bluuebunny/crossref_metadata_2025_split huggingface dataset:
Predicting Strength Properties Applying Machine Learning Techniques for Highly Heterogeneous Microbial Limestones from Brazilian Pre-Salt Reservoirs
Authors: Ferreira F. H. , Borba A. M. , Garcia P. F. V. , Santos E. S. R. , Falcão F. O. L. 
Published: August 2024

ABSTRACT:
Comprehensive knowledge of rock strength and deformability properties holds paramount importance in the E&P activities. This understanding proves critical across a spectrum of designs such as wellbore stability, sanding production, compaction, subsidence, as well as facilitating intricate 3D Geomechanical modeling, and more. This study presents a comprehensive compilation of 525 triaxial and uniaxial tests conducted on samples extracted from a highly heterogeneous limestone formation from the Brazilian pre-salt region over the course of the last 12 years. By incorporating both triaxial and uniaxial test data, the research delves into the rock's response to diverse stress conditions, contributing to the understanding of its mechanical behavior. To analyze this dataset, machine learning techniques were employed to establish correlations, specifically focusing on Uniaxial Compressive Strength (UCS) in relation to porosity and shear envelopes. This approach aimed to unveil intricate patterns and dependencies within a broad spectrum of limestone porosity levels. By harnessing the power of machine learning, the study sought to derive robust correlations that encapsulate the nuanced interplay between UCS, porosity, and shear strength. Such approach not only enhances our understanding of the complex relationships within the dataset but also offers a predictive framework for estimating UCS and CCS based on varying limestone porosities.

1. INTRODUCTION
Engineering rock mechanics plays a pivotal role in various human activities, spanning civil, mining, petroleum, and environmental engineering. In the realm of rock mechanics specific to Petroleum Engineering, professionals grapple with multifaceted challenges, including reservoir compaction, surface/mudline subsidence, fault reactivation, cap rock integrity, wellbore stability during drilling phases, onset sanding production, and hydraulic fracture design and much more. Effectively addressing these structural issues hinges on a comprehensive understanding of a triad of parameters: i) in situ stress; ii) mechanical rock properties, and iii) underground geometry. This amalgamation of parameters is encapsulated in the concept known as the Mechanical Earth Model (MEM), which has been instrumental since the early 90s.
Numerical Modeling of Fluid-Driven Fractures in Permeable Media Using Symmetric Cohesive Elements
Authors: Mejía C. , Rueda J. , Roehl D. 
Published: August 2024

ABSTRACT:
Hydraulic fracturing is one of the most widely used techniques adopted in the oil industry to enhance reservoir permeability. In traditional hydraulic fracture modeling, the numerical model simulates half of the fracture geometry by taking advantage of model symmetry. However, hydraulic fracture modeling in heterogeneous rock formations considering a fully coupled formulation can require significant computational effort, especially in 3D models. This work proposes a symmetric cohesive element to simulate fluid-driven fractures in permeable porous media. In this approach, the hydraulic fracture path coincides with the plane of symmetry of the fracture, allowing the simulation of only a quarter of the fracture geometry. The symmetric cohesive element is obtained by imposing suitable constraints on the displacement degrees of freedom. In addition, the hydromechanical properties are updated to induce symmetric hydraulic fracture propagation. The proposed technique is successfully compared against the traditional full model, demonstrating simulation accuracy with substantially reduced computational cost. The numerical results demonstrate the capability of the proposed approach to successfully simulate hydraulic fracturing under under K and propagation regimes. Finally, this approach is an attractive alternative to simulate field scale models considering heterogeneous permeable rock formations.

1. INTRODUCTION
The oil and gas industry employs the hydraulic fracturing technique to enhance unconventional reservoir permeability. The fracturing process involves the high-pressure injection of fracturing fluid to create cracks inside the rock formation, facilitating the migration of trapped hydrocarbon. However, it can lead to geomechanical problems such as seismicity (Rutqvist et al., 2013). Therefore, a better understanding of the hydraulic fracturing behavior is essential to reduce the associated environmental risks. However, the numerical modeling of hydraulic fracturing requires a better understanding of the physical mechanisms and also the ability to build field-scale models (Searles et al., 2016).
In the last decades, numerical models have been developed to simulate hydraulic fracturing problems with complex fracture geometry (J. Adachi et al., 2007). Recently, several authors developed fully coupled HM zero-thickness interface elements, which modeled longitudinal and transversal fluid flow inside the fracture (Ng & Small, 1997; Segura & Carol, 2008). A fully coupled interface element with cohesive law is adopted to model hydraulic fracture propagation in permeable porous media (Chen et al., 2009; Zielonka et al., 2014). The capability of this approach was verified through comparison with available analytical solutions (Carrier & Granet, 2012) and laboratory fracturing tests (Searles et al., 2016). However, accurate modeling of hydraulic fracturing requires refined mesh close to the fracture plane, which is computationally expensive for 3D field-scale models.
Comparison of Geochemical Reactivity of Marcellus and Caney Shale Based on Effluent Analysis
Authors: Dje L. B. , Awejori G. A. , Radonjic M. 
Published: August 2024

ABSTRACT:
In this comparative study, we analyzed the changes in elemental concentrations of hydraulic fracturing fluids after interaction with the Marcellus and Caney Shale formations. The focus was on assessing the inherent risks and environmental implications associated with flowback waters, including their impact on soil, ground, and drinking water quality, and human health safety. The chemical compositions of effluents were determined through Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Mass spectrometry (ICP-MS). The Marcellus Shale, showed concentrations of Cd, averaging 0.380 ppm far exceeding safe water thresholds. Significant levels of As, Se, B, and Pb were detected in both shales, raising concerns about soil and water contamination. Analyzing the effluents from representative samples of sections of the Marcellus (S2 and S7) and Caney (R1 and R2) indicates different geochemical responses over 4 weeks of experiments. This comparison underscores the chemical changes and environmental considerations linked to hydraulic fracturing across shale formations, suggesting the value of tailored monitoring and regulatory measures for each type.

1. INTRODUCTION
The Caney and Marcellus shales, differing in geology and geochemistry, represent distinct unconventional reservoirs. The Caney shale, is more ductile, with higher produced water volumes, (Smith et al., 2022) contrasts with the brittle Marcellus shale known for lower brine production but significant data availability. This study aims to elucidate the possible environmental health and safety issues that may arise from the hydraulic fracturing processes.
The interaction between fracturing fluids and clays presents a significant challenge. The primary base of these fluids is water, which, when introduced to clay, can induce swelling and constrict flow pathways. This phenomenon is attributed to water molecules infiltrating the layers of clay, particularly in 2:1-type clays, leading to an increased distance between layers. To counteract this, clay stabilizers are employed (Awejori et al., 2021). Despite their effectiveness, these stabilizers are considered temporary solutions. Upon completion of the fracturing process, a concomitant amount of contaminated waters (flow back), with varied content is collected at the surface. From these, we can infer the geochemical reactions and the environmental challenges associated with these waters. Flowback waters can be reinjected or used for other purposes such as irrigation. This requires adequate screening and treatment for safe use.
Elastic, Viscoelastic, and Permeability Response of Kentucky Sandstone in the Presence of scCO2
Authors: Kamali-Asl A. , Kovscek A. R. 
Published: August 2024

ABSTRACT:
We performed a series of hydrostatic and triaxial creep experiments on a Kentucky Sandstone sample using 1% NaCl brine as the pore fluid, before and after interaction with supercritical carbon dioxide (scCO2). We conducted the hydrostatic creep tests at three different pore pressures of 10, 20, and 30 MPa and three different effective stresses of 10, 20, and 30 MPa at each pore pressure, in both loading and unloading conditions. The triaxial creep tests consisted of two levels of pore pressures of [10,20] MPa, under the same confining pressure and differential stress. The bulk moduli showed strong and weak dependency on effective stress and pore pressure, respectively. As expected, creep deformation was notably larger in the triaxial tests compared to hydrostatic tests, which led to an increase in Young's modulus and a gradual loss of permeability during the triaxial tests. After interaction with scCO2, we observed a significant increase in permeability, a significant decrease in Young's modulus, and a modest increase in bulk modulus. Moreover, the triaxial creep deformation was larger after interaction with scCO2.

1. INTRODUCTION
Geological carbon storage has been proposed by many as one of the solutions to the issue of climate change, and as a bridge to transition from hydrocarbon production to renewable and clean geo-resources (Bouckaert et al., 2021). Storage of large volumes of CO2 can be achieved in porous sandstone formations, either in depleted hydrocarbon reservoirs or saline aquifers. However, there are some considerations when CO2 is injected into these sandstone formations (Orr, 2009). The role of geomechanics has often been neglected when the interplay between mechanical and transport characteristics of depleted reservoirs that are then repressurized with CO2 is considered. In particular, how the injection-induced change in the state-of-stress would affect the (i) mechanical (elastic) characteristics of the reservoir over shorter time periods, and (ii) transport characteristics (i.e., permeability) of the reservoir over longer time periods.
Numerical Analysis for the Design Assessment of Underground Mine Operations
Authors: Cammarata G. , Bui T. A. , Brasile S. 
Published: August 2024

ABSTRACT:
In the design of room-and-pillar mine systems, the loading capacity of the pillar is equally as important as the stability of the roof and walls to preserve safe working conditions and commercial ore productivity. The optimized design of pillars requires an assessment of the generated stress and available strength which depend on the mechanical behaviour of the rock mass. Moreover, the actual stress level imposed on a pillar depends also on the location of the pillars within the mine layout. These aspects cannot be properly considered by employing empirical and simplified approaches, while numerical methods provide the required accuracy in the determination of stress variations across the pillars as well as the assessment of the pillar strength. In this paper, we adopt numerical modelling to better constrain the implication of employing simplified approaches for a proper definition of the safety margins of a room-and-mine pillar layout. The results highlight the advantage of adopting advanced constitutive laws for the rock mass and discontinuities resulting in fully optimized designed solutions in terms of safe and, at the same time, economical designs.

1. INTRODUCTION
In mining excavations, rock pillars are commonly used in most underground mining methods, either temporary or permanent, to support adjacent underground openings and thus guarantee the stability of the rooms for extracting the ore safely. In the design of room-and-pillar systems a suitable factor of safety that relates the pillar strength, defined as the maximum resistance to the axial compression, to the pillar stress is required.
With this regard, empirical methods for estimating pillar strength and simplified methods for evaluating the pillar stress (i.e., tributary area method) have found wide acceptance in the mining industry. This has led to the formulation of several strength equations (e.g., Hedley and Grant 1972; Von Kimmelmann et al. 1984; Krauland and Soder 1987; Potvin et al. 1989; Sjöberg 1992; Lunder and Pakalnis 1997; Walton and Sinha 2021) which in some cases also consider account the effect of the length for rectangular pillars (e.g., Wagner 1992; Mark and Chase 1997; Dolinar et al. 2007) as well as the impact of large angular discontinuities (e.g., Esterhuizen et al. 2011). However, these methods should be used with caution (e.g., Dressel and Diederichs 2023) because they fail to consider specific failure mechanisms and do not account for the actual stress level imposed on the pillar due to the location of the pillars within the mine layout.
Coupled Reservoir-Geomechanics Simulation of CO2 Storage at the Wyoming CarbonSAFE Storage Hub
Authors: Bai Tao , Yu Ying , Jiao Zunsheng , Johnson Matthew , Nye Charles , McLaughlin J. Fred , Quillinan Scott , Peng Li 
Published: August 2024

ABSTRACT:
The Wyoming CarbonSAFE project is aimed at storing more than 50 million metric tons of CO2 over 30 years in a stacked reservoir-caprock system. To alleviate the concerns of potential geomechanical risks associated with geologic carbon storage at the study site, a coupled fluid-flow and geomechanics simulation is conducted to evaluate the geomechanical effects resulting from CO2 injection. A field-scale reservoir model is constructed based on realistic reservoir characterization data including 3D seismic, well logs, core analysis and fluid samples. Both 1D and 3D mechanical earth models are constructed to characterize the rock's mechanical properties and in-situ stress state. It is observed that roughly 84 million metric tons of CO2 can be stored in the study site. The geomechanical analysis indicates that no failure happens for most of the reservoirs and their corresponding caprock, the basement faults remain stable, and a maximum uplift of 7.92 cm is observed at the surface.

1. INTRODUCTION
Geologic carbon storage currently is treated as a promising approach to reducing greenhouse gas emissions by capturing carbon dioxide (CO2) from the industrial process or the atmosphere and then storing it in the subsurface porous media like saline aquifers, depleted oil and gas reservoirs and coal seams (Obdam et al., 2003). The purpose of the U.S. Department of Energy's Carbon Storage Assurance Facility Enterprise (CarbonSAFE) Initiative Projects is to develop commercial-scale storage sites for sequestering more than 50 million metric tons of CO2, from industrial sources, in underground geologic formations (Sullivan et al., 2020). In particular, the Wyoming CarbonSAFE project aims to capture CO2 emissions from a coal-fired power plant, named the Basin Electric Dry Fork Station (DFS) located in eastern Wyoming's Powder River Basin, and store it in three stacked reservoirs (Jiao et al., 2022).
One of the concerns associated with geologic carbon storage is the potential geomechanical risks during CO2 injection. Specifically, the pore pressure over the porous media continuously increases due to the injected CO2, then the in-situ stress state is changed correspondingly. When the reduced effective stress reaches a certain threshold, the integrity of the reservoir and caprock and the stability of preexisting faults are compromised. In the worst condition, the injected CO2 may leak through the induced fractures and reactivated faults, which poses a negative impact on the expected sealing behaviors (Rutqvist, Jonny., 2012). Therefore, these geomechanical effects should be fully characterized to ensure the containment and manage the potential geomechancial risks.
Post-Peak Multi-Stage Triaxial Testing of Miniature Rock Mass Samples
Authors: Cylwik S. D. , Childs D. W. , Mahoney D. M. , Plange K. M. , Grubb C. M. 
Published: August 2024

ABSTRACT:
Triaxial tests were performed on rock core samples with 14 confinement stages per test to investigate the post-peak strength and nonlinearity of the failure envelope for fractured rock masses. The confinement stages were tested progressively on each sample, starting at 0.69 MPa, incrementally ascending to 27.6 MPa, and then descending back down to 0.69 MPa. Three types of samples were tested: massive (no defects), continuous pre-existing defect, and jointed. The jointed samples were prepared to imitate a small-scale rock mass by confining brecciated sandstone core within heat shrink film and then mechanically breaking healed veins between the clasts with Brazilian disk load platens prior to testing. The measured post-peak strength of the samples was variable and dependent on the direction and quantity of pre-existing discontinuities within the sample. A generic failure criterion was fit to the test results to determine strength parameters for evaluation and comparison. Two empirical rock mass strength estimation methods were fit to the test results to assess if empirical methods are able to model the measured failure envelopes.

1. INTRODUCTION
Most engineering evaluations rely on empirical methods to estimate rock mass strength properties. Empirical methods generally utilize input parameters that can be readily measured in the laboratory or core shed such as the intact rock strength, fracture shear strength, or the degree of rock mass fracturing. Very few published studies have been performed on fractured rock samples to support or validate existing empirical estimation criteria (González-Fernández et al. 2023). This study presents a novel technique to prepare fissured, but fully interlocked, natural rock samples with mechanically induced fractures on pre-existing weakness planes. These samples are referred to as "miniature rock mass" samples due to their resemblance to a small-scale rock mass. Two of these samples were tested under multi-stage triaxial compression to measure post-peak strength behavior. In addition, two baseline samples were also tested to bracket the potential strength envelopes of a rock mass: one massive sample (no defects) and one sample with a continuous pre-existing defect. The resultant strength envelopes for each sample were then evaluated and fit using two different empirical rock mass strength estimation methods.
Evaluation of Fracturing Fluid Impact on the Productivity of Multi-Stage Fractured Marcellus Shale Horizontal Wells
Authors: El Sgher Mohamed , Aminian Kashy , Ameri Samuel 
Published: August 2024

ABSTRACT:
The objective of this study was to examine the effects of various fracturing fluids on proppant transport and its impact on the productivity of a Marcellus shale horizontal well with multiple hydraulic fracture stages. The available data from a Marcellus shale horizontal well were utilized to develop a reservoir model. The reliability of the model was confirmed by the close agreement between the predicted production by the model and the well production data. The impact of fracturing fluids on proppant transport during hydraulic fracturing and consequently on gas production from a Marcellus shale horizontal well were investigated by employing the reservoir models. Slickwater, compared to high viscosity friction reducers (HVFRs), was found to be less effective in horizontal Marcellus shale wells that are fractured in multiple stages. In treatment with the slickwater, all stimulation energy was directed towards the lower Marcellus shale and resulted in fractures with limited height leading to lower gas recovery. The application of the HVFRs resulted in higher fracture heights and improved production.

1. INTRODUCTION
The increasing demand for energy from unconventional reservoirs worldwide, driven by the depletion of conventional resources, has spurred technological advancements in the economic recovery of oil and natural gas from unconventional shale reservoirs. The application of horizontal drilling and hydraulic fracturing techniques in recent years has successfully unlocked substantial reserves of natural gas, making shale gas development a critical component of the global oil and gas industry, especially in North America. The effective placement of proppant in a fracture has a significant impact on the conductivity of the hydraulic fracture and the productivity of the well. During hydraulic fracturing treatments, it is common to inject a slurry containing proppant to maintain the fracture conductivity after fracture closure. The slurry is composed of a carrier fluid, which can either be a low viscosity Newtonian fluid known as "slickwater," or a high viscosity shear-thinning fluid. A suitable fracture fluid should be compatible with the formation. It is crucial that the fluid transports proppants deep into the fracture while keeping them suspended. Fluids with an inherent viscosity will likely develop the fracture width necessary for proppants to be accepted. Additionally, it should have a low friction pressure loss and sufficient stability to retain its viscosity during treatment.
Laboratory Evaluation of Natural Fracture and Hydraulic Fracture Interactions Using Digital Image Correlation
Authors: Shandilaya Shivesh , Roshankhah Shahrzad 
Published: August 2024

ABSTRACT:
Hydraulic fracture (HF) refers to inducing fractures in a solid material by injecting a fluid at a high rate into it. Understanding the patterns of induced hydraulic fractures within a rock mass is of high importance to many energy geosystems. In this experimental study, the pattern of induced HFs is evaluated by utilizing digital image correlation (DIC). Specifically, we investigate the interactions between a hydraulic fracture (HF) and a pre-existing natural fracture (NF). Using DIC, we examine the evolution in the local strain field in an intact and a pre-cut PMMA specimens as water is injected into the loaded specimens. From theory, it is anticipated that an HF initiates at the blunted notch fabricated at the top of the model wellbore in the PMMA samples and propagates upward as the applied boundary conditions require. This is verified for the intact PMMA specimen in this experimental study. The presence of an NF however forces the HF to curve and deviate into the NF. The interactions between induced HF and pre-existing natural fractures depend on the stress anisotropy, the relative orientations of natural and hydraulic fractures, and the bonding strength of natural fractures.

1 INTRODUCTION
In many energy geosystems, such as enhanced geothermal and unconventional fossil energy systems, enhancing reservoir permeability relies on strategically creating and expanding fracture networks through hydraulic stimulation. This technique centers on the deliberate interaction between artificially induced hydraulic fractures (HFs) and the pre-existing network of natural fractures (NFs) within the subsurface geological formations. Understanding this interaction is crucial, as it directly influences the effectiveness of production and the extent of induced seismicity (Warpinski & Teufel, 1987; Zhang et al., 2020; Chang & Yoon, 2022). This approach aims to initiate new fractures and extend and interconnect to existing fractures, thereby optimizing the reservoir's permeability and fluid flow pathways. Interactions between HFs and NFs are influenced by various factors such as the angle of intersection between the fracture planes, the prevailing stress field within the reservoir, NF properties, rock matrix permeability, and fluid properties, among others (Warpinski & Teufel, 1987). An intricate convolution among these factors determines the fracture interaction scenarios, like their propagation, arrest, slippage, dilation, etc. (Jeffrey et al., 2009; Chang et al., 2015).