bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pressure Transient Analysis for Wellbore Mechanical Formation Damage Control Near No-Flow Boundaries Using an Asymptotic-Perturbation Method
Authors: Fernandes F. B. , Braga A. M. B. , Souza A. L. S. , Soares A. C. 
Published: September 2023

ABSTRACT
Identifying no-flow boundary areas is essential for a successful exploratory and production campaign during the development of an oil field. This work develops a new unsteady two-dimensional (2-D) integro-differential solution for permeability loss monitoring in a well near a sealing fault. The model presented in this study allows for solving the nonlinear hydraulic diffusivity equation (NHDE) with an oil source term. To approach this phenomenon, a new deviation factor is derived and coupled to a first-order series expansion. The proposed solution was calibrated by a finite-difference-based simulator named IMEX® broadly used in reservoir engineering works, and the results were accurate. The results clearly present the instantaneous permeability decay effect by a deviation when compared to the linear solution in a semi-log plot. The main advantages of the proposed solution are the accuracy, availability of a wide table of the GFs, ease of implementation, and computational cost savings. Hence, the modeling developed in this paper becomes a useful and attractive tool for predicting and monitoring permeability loss, oil flow rate specification, reservoir history matching and calibrating new models.

INTRODUCTION
The nonlinear oil flow through porous media near sealed boundaries has a vital role in reservoir damage evaluation and engineering because various oil and gas pressure-sensitive formations are located near sealed zones world-wide (Fernandes, 2022; Fernandes et al., 2022a,b,c). Sealing faults may significantly impact the fluid flow patterns within a petroleum reservoir, (Kuchuk and Kabir, 1988; Kuchuk, 2009). Thereby, the knowledge of fault zones is essential for the economic viability analysis of exploration projects to prevent early depletion during the well-reservoir performance management, (Knipe et al., 1998; Nurafiqah et al., 2020). The mathematical modeling of the permeability pressure-dependent effect through the nonlinear hydraulic diffusivity equation (NHDE) with source term is still challenging in the petroleum industry. Therefore, accurate analytical models for the nonlinear source term have been extensively researched to save computational resources and calibrate new reservoir models. Image data (ID) and pressure transient analysis (PTA) constitute useful, practical tools to identify sealed zones, (Bengtson, 1981, 1982; Goetz, 1993; Adams and Dart, 1998). Therefore, new advances in seismic inversion algorithms and analytical models are sought for no-flow boundary region identification to provide adequate oilfield development, (Schuller and Vogele, 2019).
Numerical Simulation of Hydraulic Fracture Propagation in Coalbed with Cleats
Authors: Fuchun Tian , Yan Jin , Lin Shi , Ziyuan Cong , Yuwei Li 
Published: September 2023

ABSTRACT
Cleats play a crucial role in the propagation of fractures during coalbed hydraulic fracturing. However, current numerical methods still suffer from significant drawbacks in terms of computational efficiency and fracture trajectory prediction. In this study, we used the displacement discontinuity method (DDM) to calculate the stress in the coal body and corrected fluid leakage using the Brinkman equation. We also derived a mechanical criterion for cleat failure under different conditions and proposed a new model for fracture propagation in coalbeds with orthogonal cleats. Our numerical results indicate that simple plane fractures are more likely to form when the horizontal stress difference in the coalbed is greater. When the angle between the cleats and the horizontal principal stress is close to 45°, hydraulic fractures are more likely to activate the cleats. The friction coefficient of the cleats only affects the net pressure within a specific range in the critical crack. As the cohesion of the cleats decreases, the minimum net pressure required for shear failure decreases significantly, making shear failure more likely. We also introduced a reconstruction coefficient, η, to evaluate the effectiveness of coalbed fracturing stimulation. When the cleats are activated, the reconstruction coefficient η increases, indicating that the flow width per unit fracture length improves and is more conducive to production.

INTRODUCTION
Against the backdrop of carbon emission reduction, coalbed methane (CBM) is becoming an increasingly significant clean energy source for future use, playing a crucial role in energy supply and economic development (Wang et al., 2021; Zhang et al., 2018; Li et al., 2020; Fan 2021). Hydraulic fracturing is a well-established technology for CBM production and has proven to be highly effective over decades of application (Ai et al., 2021; Li et al., 2017). The morphology of fracture propagation in coalbeds is complex, with numerous factors affecting the process. Along with coal's low strength, low elastic modulus, and high Poisson's ratio, the presence of cleats also significantly influences fracture propagation. (Li et al., 2019a; Li et al., 2019b; Su et al., 2005; Xu 2020). Cleats within the coalbed develop in an orthogonal network, and their interaction with hydraulic fractures (HF) can alter the HF propagation direction, adding complexity to the fracture system and posing challenges for predicting the trajectory of HF within coalbeds. Despite the significance of cleats on fracture propagation in coalbeds, there is still a lack of theoretical calculation methods capable of accurately simulating and predicting the morphology of fracture propagation.
Investigating Effects of Cryogenic Treatment on Physical and Mechanical Properties of Geothermal Formation Samples – An Experimental Study
Authors: Thiyagarajan Sugan Raj , Emadi Hossein , Altawati Faisal , Soliman Mohamed , Watson Marshall 
Published: September 2023

ABSTRACT
Geothermal formations are generally fractured using water-based fracturing fluid, which has several issues, such as high-water consumption and environmental issues. In this study, a waterless stimulation method was used on granite samples. Studying the optimum injection time of LN2 in HDR formations for efficient fracturing will be beneficial for the future of EGS. Effects of varying LN2 exposure time on heated granite samples and their mechanical and physical properties were studied. Eleven core samples were heated to different temperatures, up to 482°F, and treated with LN2 for different times of 10,20, and 30 minutes. CT scan, porosity, permeability, and ultrasonic velocities tests were conducted both before and after LN2 treatment. Later, unconfined compressive strength and X-Ray Diffraction tests were conducted on the treated samples. The results indicated that the physical and mechanical properties of the core samples were altered after implementing LN2 treatment. The permeability enhancement was more significant than the porosity improvement. The ultrasonic velocities of the samples decreased after the cryogenic treatment owing to the creations of the new fractures inside the samples. Increasing the treatment temperature and treatment time results in an increase in the permeability of samples, which will improve the heat extraction in geothermal formations.

INTRODUCTION
As an abundant and sustainable energy source, geothermal energy, particularly stored in hot dry rocks (HDR), can play a critical role in reducing the fossil fuel consumption and the associated environmental dangers such as carbon dioxide emissions, water pollution, and acid rain (Lu, 2018; Y. Shi et al., 2018; Tester et al., 2006). The amount of heat present in HDR is large, approximately 1.4 × 1025 J in the United States and over 2.52×1025 J in China, and the temperature is higher than in the other geothermal systems, 300°F – 1200°F (Song et al., 2018). The most suitable rock type for HDR is granite or other crystalline basement rock with temperatures from 300°F to 950°F at depths from 3 to 4 miles (Potter et al., 1974). The method of producing energy from hot dry rocks is known as Enhanced Geothermal System (EGS). Even though there are startling numbers regarding the potential of EGS from numerous studies around the world, tapping energy from HDR is still in progression (Breede et al., 2013).
Sub-Core Scale Characterization of Microbial Invasion Impact in Carbonates: Implications for Mechanical Alteration
Authors: Ngoma M. C. , Kolawole O. , Elinski M. B. , Thomas R. , LaGrand R. 
Published: September 2023

ABSTRACT
Biogeomechanics is a novel and resourceful approach to assessing the impact of biological processes on the mechanical properties and behavior of rocks and rock-like materials. However, there is still a lack of knowledge on how far an in-situ bacterial growth can invade a reservoir rock with time and what its long-term impacts at nano- to micro-scale are in the invaded reservoir. This study uses non-destructive methods to investigate time-dependent nano-scale extent of biogeomechanical and morphological alterations in carbonate rocks due to microbial invasion. We conducted a microbial treatment of carbonate rock samples using a distinct microbial solution over a period of 30, 60, 90, and 120 days at a temperature of 42°C. Subsequently, the sub-core scale properties of untreated and post-treatment carbonate rocks were measured using Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) to assess the changes in surface roughness and pore structure. Finally, we compared the untreated and microbially treated samples and assessed the implications for mechanical properties to better understand how microbial invasion could impact carbonate rocks. The results suggest that distinct microbes can continue to invade and alter the formation over time causing dissolution and disintegration of the rock matrix, which may yield a reduction in the mechanical integrity of the microbially impacted carbonate rock.

INTRODUCTION
Interaction between rocks and fluids can have multiple effects on its mechanical and mineralogical properties. Several studies have previously investigated the potential applications of these property changes in various fields such as the control of seepage in underground excavations (Phillips et al., 2013), geological CO2 storage (Kolawole et al., 2021a; Kolawole et al., 2022a), enhanced hydrocarbon recovery (Nikolova & Gutierrez, 2020; Kolawole et al., 2022b), wellbore cement integrity after exposure to corrosive environments (Kirkland et al., 2020; Kolawole et al., 2021b), and many other engineering-related processes. For example, in one study, researchers evaluated the grouting of rock fractures characterized by a fine-scale aperture with calcium carbonate due to microbial activity (Minto et al., 2016). This microbe was used for the treatment of samples over 12 days, and the results showed that the hydraulic aperture was reduced (Minto et al., 2016).
Strain Localization in Jointed Rockmass Analog Laboratory Specimens Under Compression
Authors: West I. G. , Walton G. , Gonzalez-Fernandez M. A. , Alejano L. R. 
Published: September 2023

ABSTRACT
Field-scale rock formations (i.e. rockmasses) are composed of sections of intact rock separated by a preexisting joint network. As rockmass deforms, strain accumulates within the intact rock and slip occurs along the preexisting joints. However, the magnitude of strain within the intact rock sections are not necessarily equal everywhere throughout the rockmass due to the presence of the discontinuities. In general, testing representative rockmass specimens in the laboratory is difficult because of the required size. As an alternative, small-scale rockmass analog laboratory specimens can be used to investigate trends in rockmass behavior. This research evaluates the mechanical behavior of rockmass analog specimens of Carrara marble containing two orthogonal sets of smooth joints. Both intact and the jointed specimens were tested under triaxial compression with 1 and 12 MPa of confinement. Axial and radial deformation within each section of intact rock in the specimens were recorded with separate strain gages, and strain gages in these same positions were also attached to intact specimens for comparison. Notable radial strain heterogeneity was observed in the jointed specimens and this heterogeneity was suppressed under higher confinement levels. Strain was also found to localize in intact rock blocks with higher surface area to volume ratios.

INTRODUCTION
Field-scale rock formations are commonly referred to as rockmasses, which are composed of sections of intact rock separated by a network of preexisting discontinuities (Mendes et al., 1966). Such discontinuities can include joints (i.e. fractures), shear zones, faults, and other structural planes (Cui et al., 2020), which are formed from varying stress fields throughout the rockmass's tectonic history (Mandl, 2005). The presence of discontinuities reduces the strength of the rock and affects other aspects of its mechanical behavior (Hoek and Brown, 1997). Rockmasses are more difficult to test in the laboratory compared to intact rock because representative rockmass specimens are typically on the scale of meters. Large triaxial testing apparati are uncommon and typically allow for a maximum specimen diameter of 1 meter, which is not sufficient for many rockmasses with joint spacing of multiple meters (Muschler and Natau, 1991; Natau, 1977; Singh and Huck, 1972; Vergara et al., 2015).
Polyaxial Failure Criteria in Borehole Breakout Stress Analysis
Authors: Trzeciak M. , Sone H. 
Published: September 2023

ABSTRACT
Analysis of borehole wall failures, breakouts, is the primary method of constraining the maximum horizontal stress in deep wells. To estimate stress using the breakout method, one needs to measure the breakout width from image or caliper logs, and use a failure theory to predict stress that led to the development of the measured breakout. Most commonly, Mohr-Coulomb failure criterion is used which disregards the influence of intermediate stress on strength. Different polyaxial criteria have been proposed to include this effect. Here, we first review selected polyaxial criteria: Drucker-Prager, Mogi and modified Wiebols-Cook, and we conclude that their application in breakout analysis is cumbersome and often unreliable. One reason for these problems is that the criteria are defined using octahedral stresses or invariants, while the breakout analysis is most easily done in the principal stress space. Therefore, the polyaxial criterion can be defined as a simple relation between maximum and intermediate stresses. We propose to define such an empirical criterion as a second order polynomial which fits trends observed in polyaxial laboratory strength data.

INTRODUCTION
Knowledge of in situ stress is essential for many geological engineering applications including: borehole stability, hydraulic stimulation, induced seismicity, and others (e.g. Zoback, 1992, 2007; Jaeger et al., 2007; Heidbach et al., 2018). Among the three principal stresses, the maximum horizontal stress (σH) is the most challenging to constrain (Zoback et al., 2003). The most commonly used method is based on analysis of borehole wall compressive failures, i.e. breakouts. Breakout analysis requires two components: i) the breakout geometry observed from image or caliper logs, and ii) a failure theory to predict stress that led to the development of a breakout with the measured geometry.
Most commonly, the Mohr-Coulomb criterion is used in borehole wall strength analysis and its failure is predicted when the hoop stress reaches a critical value (Barton et al., 1988). However, such approach disregards the influence of the intermediate principal stress (σ2) on rock strength (understood as the maximum principal stress, σ1, at failure) which has been described in numerous experimental studies (e.g. Mogi, 1971; Michelis, 1985, 1987; Haimson and Chang, 2000; Chang and Haimson, 2000; Ingraham et al., 2013; Ma and Haimson, 2016; Lee and Haimson, 2011). Therefore, several polyaxial failure criteria which include the σ2 dependence of strength has been proposed and applied in borehole breakout analyses (Zhou, 1994; Ewy, 1999; Al-Ajmi and Zimmerman, 2005; Chang et al., 2010).
A Case Study of Shale Gas Well Casing Deformation in Longwall Chain Pillars Under Deep Cover
Authors: Zhang Peter , Su Daniel , Van Dyke Mark , Kim Bo Hyun 
Published: September 2023

ABSTRACT
Shale gas wells in longwall chain pillars are subject to longwall-induced overburden movements. Longwall mining on either side of the chain pillars can induce deformations in gas well casings. The casing deformations induced by longwall mining has raised the safety concern that casing integrity might be diminished so that intrusive shale gas could leak into the longwall mine with serious consequences. This study deals with longwall-induced casing deformations of eight shale gas wells in the chain pillars between two adjacent longwall panels in the Pittsburgh coal seam under a cover depth of 314 m and a mining height of 2.1 m. The longwall panels were 457-m wide, and the chain pillars were 66-m wide. The longwall faces passed by the shale gas wells as each adjacent longwall panel was retreated. Gas well casing deformations were measured by a multi-finger caliper after each panel was mined. The first panel mining induced casing deformations less than 1.7 cm above the coal seam horizon. The second panel mining caused an increase of casing deformation up to 20%–30% on average. The casing deformations were also predicted by the FLAC3D modeling technique based on site-specific mining and geological conditions. The study demonstrates that the predicted casing deformations are generally in good agreement with the measurements. The study shows that the casing deformations first occur at the weak/strong rock interfaces after first panel mining and then increase by a small amount at the same locations after second panel mining. The study reveals that longwall-induced casing deformations under deep cover are smaller than those under shallow cover. The study also provides a quantitative method for using numerical modeling to assess the stability of shale gas wells in longwall chain pillars.

INTRODUCTION
Gas wells drilled in longwall pillars are influenced by longwall mining. Due to longwall-induced subsurface ground movements, the gas wells in the vicinity of longwall panels are subject to longwall-induced stresses and deformations. Excessive stresses and deformations induced in gas well casings could lead to a casing breach. More safety concerns have been focused on unconventional shale gas wells in the presumption that the casing breach could allow high-pressure gas to leak into the mine, potentially causing a fire and explosion. Over the past decade, more than 1,500 shale gas wells have been drilled in the current and future reserves of the Pittsburgh coal seam. The impact of longwall mining on these shale gas wells will have to be evaluated as future longwall panels are mined. Therefore, it is important to quantify longwall-induced subsurface movements and casing deformations and to develop reliable models to assess the stability of shale gas wells in longwall pillars.
Advanced Fracturing Modeling Through Combining Fracture Model and Geomechanics
Authors: Gong Yiwen , Fan Meng , Yang Lifeng , Wang Xin , Xie Hongbing , Mao Zhenyu , Liu Chuxi , Yu Wei , Leines Joseph , Miao Jijun 
Published: September 2023

ABSTRACT
Due to the highly uncertain nature of unconventional reservoirs and difficult monitoring of the engineering effectiveness, a reliable, accurate, and efficient fracture propagation model is essential to help operators understand/plan their assets. The fracture modeling sensitivity study is a comprehensive investigation of the key factors that influence the behavior of hydraulic fractures in subsurface rock formations. This study utilizes advanced numerical simulation techniques to model the propagation of hydraulic fractures in various geomechanics conditions and evaluates the sensitivity of fracture behavior to changes in the design parameters and rock properties. Additionally, the study evaluates the sensitivity of fracture behavior to changes in the hydraulic fracturing design parameters, such as injection rate, fluid viscosity, and proppant concentration. The results demonstrate that these parameters can significantly affect fracture geometry and propagation behavior, highlighting the importance of accurate design and optimization of hydraulic fracturing operations. Overall, the fracture modeling sensitivity study provides valuable insights into the mechanics of hydraulic fracture propagation and the key factors that influence it. The findings can inform the design and optimization of hydraulic fracturing operations, ultimately improving the efficiency and effectiveness of hydrocarbon extraction from unconventional reservoirs.

INTRODUCTION
Hydraulic fracturing involves the injection of high-pressure fluid into a wellbore, creating fractures in the rock to allow for the extraction of trapped hydrocarbons. Accurate modeling of hydraulic fractures is crucial for optimizing production and reducing environmental impact. One such modeling approach is the Peudo 3D Displacement Discontinuity Method (P3D DDM), which has gained popularity due to its ability to simulate complex fracture geometries.
The sensitivity study of hydraulic fracture modeling using P3D DDM is an important research topic that aims to understand the effects of various input parameters on fracture behavior. In this study, researchers perform a series of simulations by varying parameters such as fluid viscosity, injection rate, and fracture toughness to investigate their impact on fracture growth and propagation. The results of the study can provide valuable insights into the design and optimization of hydraulic fracturing operations, which can lead to improved efficiency and reduced environmental impact.