bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Hydrogen on Class H Well Cement's Properties Under Geological Storage Conditions
Authors: Maury Fernandez D. , Emadi H. , Thiyagarajan S. , Hussain A. , Ispas I. 
Published: September 2023

ABSTRACT
Depleted oil and gas reservoirs are one of the most promising alternatives for underground hydrogen storage due to their sealant capacity and presence of residual hydrocarbon, which reduces the requirements for cushion gas and operational costs. Its existent infrastructure is also attractive owing to its lower investment costs. However, wells and facilities have been designed and constructed for operating with hydrocarbons and might be affected by the presence of hydrogen. Failure in well integrity could lead to hydrogen leakage, compromising the storage security for hydrogen projects. Hence, understanding hydrogen's effects on wellbore components such as casing and cement sheath becomes important. Although the effects of hydrogen on steel have been widely studied, effects of hydrogen on cement sheath and its properties are currently unknown. This study aims to evaluate the change in properties of neat Class H cement after being exposed to hydrogen under geological storage conditions (1500 psi and 120°F) for different time periods. Properties such as permeability, porosity and dynamic elastic properties like Young's Modulus and Poisson's ratio, were measured and analyzed before and after hydrogen exposure to investigate its effects on cement sheath. The experimental results revealed an increase in the permeability and porosity of the cement samples after hydrogen exposure. Also, hydrogen affects the dynamic elastic properties of the samples. The results of this study could be used to assess the wellbore integrity risks in depleted oil and gas reservoirs.

INTRODUCTION
Hydrogen is expected to play a fundamental role in the future global energy system. Its outstanding energy capacity (120 MJ/kg) (Abe et al., 2019) combined with its clean combustion, makes it one of the most promising alternatives as an energy carrier (Hosseini & Wahid, 2016). Although, hydrogenis the most abundant element on earth, it is not found freely in a sufficient amount, but it can be produced from non-renewable sources in multiple ways such as hydrocarbon reforming, hydrocarbon pyrolysis and subsurface production (in-situ combustion), or from renewable sources through water electrolysis. Once produced, hydrogen is burned and energy is conveyed as heat (Najjar, 2013; Salahshoor & Afzal, 2022; Veras et al., 2017).
A Data-Driven Intelligent Approach to Predict Shear Wave Velocity in Shale Formations
Authors: Mustafa Ayyaz , Tariq Zeeshan , Iqbal Arfa , Naeem Maryum 
Published: September 2023

ABSTRACT
Shear (S-) waves velocity plays a critical role while deriving rock mechanical characteristics such as Poisson's ratio and Young's modulus. Mostly, the S-wave log is not available for all the wells due to associated high costs. Therefore, precise estimation of S-wave velocity is deemed necessary through prediction models. The study aims to develop reliable machine learning models for predicting S-wave velocity in shale formation using conveniently available wireline logs. Six robust machine learning techniques such as decision tree (DT), artificial neural networks (ANN), K-nearest neighbor (knn), random forest (RF), extreme gradient booster, adaptive gradient boosting were implemented for the model development. Training and testing results revealed high accuracy and robustness of all six proposed intelligent models in terms of high coefficient of determination (R2) and low root mean squared (RMSE) and average absolute percentage (AAPE) errors. However, comparison revealed that ANN model outperformed all other ML models exhibiting highest R2 (0.96) and lowest AAPE (0.91) and RMSE (2.96) errors for testing prediction results. The proposed intelligent models are capable of providing the swift, robust, and cost-efficient solution to obtain the S-wave velocity in shale formation that would be valuable in deriving the other rock mechanical properties.

INTRODUCTION
Shear wave velocity is of vital importance in estimating various geomechanical properties especially for petrophysical and geophysical investigations. Shear waves, in contrast to compressional waves, cannot travel through liquids. As a result, these data aid in identifying the characteristics of rock, such as the fluid content of its pores and its lithology. Also, understanding how pore spaces, lithology, pore fluid, and shear wave velocity relate to one another gives important reservoir information (Khatibi and Aghajanpour, 2020). One of the key objectives of geomechanical investigations is the development of the mechanical earth model, which can be accomplished using this parameter. The rock's mechanical characteristics and stress status are computed using the mechanical earth model (Plumb et al., 2000). Geomechanics, which takes into account the mechanical properties of rock, is crucial for planning activities like drilling, exploration, completions, and reservoir engineering. For safe and efficient drilling, in particular, it is crucial to comprehend the risks posed by ground stress, which necessitates the creation of geomechanical models.
Fluid-Solid Coupled Production Model of Fractured Horizontal Well in Glutenite Tight Oil Reservoirs
Authors: Yang Shuai , Yang Zhanwei , Chen Ang , Zhou Peiyao , Liu Kaixin , Wang Song 
Published: September 2023

ABSTRACT
Clarifying the seepage mechanism and production decline law of fractured horizontal wells in glutenite reservoirs is crucial for guiding fracturing design, optimizing the production system, and realizing efficient reservoir development. In this paper, a production model suitable for fractured horizontal wells in glutenite tight oil reservoirs was established, based on the principle of fluid-solid coupling and comprehensive consideration of the characteristics of reservoir rock deformation and permeability stress sensitivity during production. An example application was used to verify the accuracy of the model, and the factors affecting production were discussed. The research results demonstrate that the model can reflect the dynamic change characteristics of the stress field and permeability during the production process. The production differential pressure must be controlled within the critical production differential pressure to avoid shear compaction in some formations near the wellbore, which could greatly reduce permeability and production. Among the fracturing engineering parameters, fracture spacing mainly affects the early linear seepage of the fractured horizontal well, whereas fracture half-length mainly affects the mid-late radial seepage. Increasing the fracture half-length has a more significant impact on increasing the long-term cumulative production of fractured horizontal wells in glutenite reservoirs.

INTRODUCTION
The Mahu Oilfield is situated in the Mahu Sag of the Junggar Basin, Xinjiang, with geological reserves of 1.24 billion tons and proven reserves of 520 million tons. It is currently the world's largest glutenite tight oil reservoir (Anon, 2018; He and Zhang, 2017). Thanks to the development of large-scale volumetric fracturing technology for horizontal wells, significant breakthroughs have been made in production in this area, making it the primary region for increasing reserves and production in the Xinjiang Oilfield (Li et al., 2020). However, glutenite tight reservoirs typically possess poor physical properties, strong heterogeneity, and weak matrix fluid supply capacity (Gao, 2022; Hao et al., 2021). Consequently, the pressure attenuation speed is often rapid after fracturing in certain blocks, resulting in insufficient continuous production capacity. Therefore, understanding the seepage mechanism and production decline law is critical for guiding fracturing design, optimizing the production system, and achieving efficient development of glutenite tight oil reservoirs.
Legitimacy of the Hertzian Assumptions for Poroelastic Spherical Indentation
Authors: Liu Ming , Huang Haiying 
Published: September 2023

ABSTRACT
Key assumptions in establishing the classical Hertzian solution for contact between two linear elastic spherical bodies are that the contact is non-conforming and the contact radius is assumed to be much smaller than the radii of the two spheres. For the particular case when one rigid sphere is pressed against a linear elastic half space, the contact radius is only related to the radius of the sphere and the depth of penetration. Poroelastic contact has recently become a subject of interest for poroelasticity characterization of fluid-filled porous media. When a rigid sphere gets in contact with a poroelastic half space, the Hertzian assumption on the contact radius is still applicable at both the undrained and drained limits. However, an open question yet to be addressed is whether this assumption is legitimate for the transient phase. In this work, we address this fundamental question for two particular classes of poroelastic spherical indentation by first analyzing the problems theoretically assuming the Hertzian assumptions still hold and then conduct finite element simulations by modeling the indentation action through a frictionless contact algorithm based on the penalty method. The results indicate that though rigorously speaking, poroelasticity could result in deviation from the Hertzian assumption during the transient phase, for the particular cases involving step-displacement or step-force loading, the Hertzian assumption on the contact radius is legitimate if the objective is to determine the integrated force or displacement response of the indenter.

INTRODUCTION
Hertzian solution for frictionless contact between two linear elastic bodies (Hertz, 1881) is the theoretical basis for material characterization using spherical indentation to measure mechanical properties such as hardness, strength and toughness (Johnson, 1982, 1987; Lawn, 1993). Recent experiments with fluid filled porous materials such as polymeric gels and hydrated bones have demonstrated that spherical indentation could also be an effective technique for poroelasticity characterization (Hu et al., 2010; Kalcioglu et al., 2012; Oyen, 2008; Galli and Oyen, 2008; Lai and Hu, 2017, 2018; Islam and Oyen, 2021). In theory, if a rigid sphere is pressed into a linear poroelastic half space consisting of incompressible constituents, elastic constants can be determined from the undrained and drained limits according to the Hertzian contact solution. For the particular cases when the sphere is subjected to either step-displacement or step-force loading, hydraulic diffusivity or the coefficient of consolidation can be obtained from the transient response by matching the measured indentation force or displacement as a function of time against a master curve. Attempts have been made to establish this type of master curves numerically for step displacement loading (Hu et al., 2010; Lai and Hu, 2017) and semi-analytically for step force loading (Agbezuge and Deresiewicz, 1974; Oyen, 2008).
3D Image Analysis of Granular Force Chains
Authors: Li W. , Juanes R. 
Published: September 2023

ABSTRACT
Granular media constitute the most abundant form of solid matter on Earth and beyond, from coffee beans to beach sand to Martian soil. When external forces are applied to granular media, the forces are transmitted in the media through a network of contacts–force chains. Understanding the temporal evolution and spatial structure of these force chains is a fundamental goal of granular mechanics. A new imaging technique, interference optical projectional tomography (IOPT), was introduced by Li and Juanes (2023) to visualize and quantify force chains in 3D granular media, and their evolution under triaxial shear. Here, we present a suite of 3D image analysis functions that were developed to study the morphology of the 3D granular force chains visualized by IOPT. Combined with the built-in functions in MATLAB, our image analysis toolkit allows us to quantitatively describe the morphology of 3D force chains in granular media under triaxial shear. Our study shows that increasing shear stress results in increasing force chain lengths and dip angle, and that the mechanistic origin of shear failure is the buckling of the force chains.

INTRODUCTION
Under the action of external stresses, grains in granular materials form an inhomogeneous contact network, which carries most of the external load by way of force chains. The resultant network pattern of these force chains can, in turn, help us determine the shearing and isotropic compression states in the granular media (Majmudar and Behringer, 2005). Similar filamentary patterns have been observed in other natural systems, such as dissolution wormholes (Daccord and Lenormand, 1987; Li et al., 2019b,c,a, 2022), fracture channels (Detwiler et al., 2003; Deng et al., 2016), viscous fingering (Måløy et al., 1985; Zhao et al., 2019), invasion percolation (Wilkinson and Willemsen, 1983; Zhao et al., 2016), hydraulic fractures (Lemaire et al., 1991), river networks (Rodriguez-Iturbe and Rinaldo, 2001; Abrams et al., 2009) and blood vessels (Szymczak and Cieplak, 2010; Zukowski et al., 2022). The temporal evolution and spatial structure of these patterns are helpful for our understanding of the underlying physics of the processes. Therefore, it is important to have the ability to analyze these network patterns quantitatively.
Replicating S-Shaped Composite Strength Response Using Bonded-Block Modelling: Capturing Dual Nature of Extensional Versus Shear Fracturing of Brittle Rock Mass
Authors: Farahmand Kiarash , Diederichs S. Mark 
Published: September 2023

ABSTRACT
As mining operations pursue deeper and larger excavations, the accurate assessment of the risk of excessive rock deformations caused by brittle fracturing and dilation/bulking near excavation boundaries becomes increasingly important. To address this, the bonded-block modeling (BBM) approach such as UDEC-Voronoi has been widely used to simulate the complex brittle rock fracturing process and predict the shape of the excavation damage zone (EDZ) developed around underground openings. To realistically predict the EDZ shape, the BBM must be calibrated to accurately replicate the progressive failure of the brittle rock mass, characterized by a soften-hardening or composite S-shaped strength response. This can be achieved by specifying a number of input parameters based on fracture mechanics principles and a suitable calibration procedure. This approach allows for simulation of the in-situ brittle fracture processes. However, the available calibration methods are inadequate in capturing the dual nature of extensional versus shear fracturing of brittle rock masses due to their focus on laboratory sample fracturing behavior rather than large-scale rock response under in-situ stress paths. This paper provides practical recommendations for fine-tuning BBM input parameters from laboratory to field scales to reproduce observed failure mechanisms in-situ, advancing BBM as the state of practice for predicting overbreak formation in deep tunnels. The paper uses a hydroelectric tunnel in laminated sedimentary formations as a case study to calibrate the BBM model to the rock's S-shaped brittle strength. The calibrated micro-mechanical approach effectively captures the post-yield response of the rock mass, which is the key controlling mechanism in damage development around deep, lightly jointed grounds. The results demonstrate that for a realistic EDZ development and accurate capture of the mechanistic processes, BBM parameters must be calibrated to the long-term in-situ strength rock mass, rather than its short-term laboratory strength. The well-calibrated BBM model can be a practical and verified numerical tool for understanding and predicting damage formation around underground excavations.
Numerical Study of the Influences of Dynamic Loading and Unloading Rates on Fracturing
Authors: Cao Wen , Younis Rami M. 
Published: September 2023

ABSTRACT
Dynamic loading offers the potential to induce densely connected fractured pore space over large bulk volumes of impermeable rock. An understanding of the impacts of the dynamic loading and unloading rates on the resulting fracturing can guide the design of discharge technologies. This work numerically investigates the dependence of the extent of fracturing on dynamic loading characteristics. We reconcile a high-fidelity model (finite-discrete element method with nonlinear fracture mechanics) with experimental observations. The model is subsequently used to simulate various loading scenarios spanning laboratory to field scale conditions.

INTRODUCTION
In contrast to hydraulic fracturing, high-energy dynamic loads generate radial fractures which are not influenced by formation stress anisotropy. This removes the need for determining the in-situ stress orientation, which is a necessary factor in designing horizontal wells that undergo multiple hydraulic fracturing treatments. This study aims to investigate the effect of different dynamic load functions on seismic fracturing.
One way to create high-energy dynamic loads is to use explosives (e.g., Grady et al. (Grady et al., 1980), Banadaki et al. (Banadaki, 2010), Zhang et al. (Zhang et al., 2017), and Jeong et al. (Jeong et al., 2020)). Explosives generate loading pulses with a maximum peak pressure that can exceed 1 GPa and a rise time of the pressure waveform on the order of 1 to 2 microseconds. Experiences using explosives are well-documented and span applications in various materials like granite, shale, and PMMA. The body of reported experiments shows that the extent of crack propagation depends on the energy released by the explosive charge, although a quantitative understanding of this relationship remains elusive for formations in the deep subsurface which cannot be observed directly or with great resolution. Another type of technology delivers the dynamic load using shock waves created in liquid. Hamelin et al. (Haimson and Fairhurst, 1967), Maurel et al. (Maurel et al., 2010), Chen et al. (Chen et al., 2012), and Xiao et al. (Xiao et al., 2018) for instance, applied Pulsed Arc Electrohydraulic Discharges (PAED) to produce shock waves in water. These loading profiles typically involve a longer time for the load to reach its peak. Moreover, in the case of laboratory experiments, reflections of shock waves from the finite samples may create extra fractures. To study the potential of formation fracturing at the field scale, large sample sizes, a wide variety of high energy loadings, and accurate diagnostics are needed. Given the challenge and costs of such extensive experimentation, numerical simulation can offer a useful alternative to narrow down the range of pulses to be investiated.
Thermal Effects Reducing Minimum in Situ Stress Can Happen Faster Than You Think
Authors: Azevedo C. T. , Schwalbert M. P. , Neumann L. F. 
Published: September 2023

ABSTRACT
It is known that when fluids are injected into an offshore well, the temperature of the injected fluid is typically cooler than the in-situ reservoir temperature. A region of cooled rock forms around the well and this cooled region contracts, leading to a decrease in horizontal in situ stresses near the well. Such effect is always related with waterflooding or other secondary or tertiary recovery processes in long period of time, such as days or months of injection. This article will show field evidence that thermal effects can happen in a few minutes or in a couple of hours, in formations that combine high Young Modulus and high reduction in temperature during injection. This article will also present a few analyses using CFD simulation and an analytical simplified solution of the cooling effect of the reservoir during fluid injection. This will give sensibility of the orders of magnitude of the stress reduction in this condition and the fracture geometry that is being created.

INTRODUCTION
It is known that when fluids are injected into an offshore well, the temperature of the injected fluid is typically cooler than the in situ reservoir temperature. A region of cooled rock forms around the well and this cooled region contracts, leading to a decrease in horizontal in situ stresses near the well. Such effect is usually related with waterflooding or other secondary or tertiary recovery processes in long period of time, such as days or months of injection.
Settari and Walters (2007) note that a hydraulic fracture is induced in a well when the bottomhole injection pressure exceeds the fracture propagation pressure, which is a function of the smallest in situ principal stresses, usually a horizontal stress. In this sense, Perkins and Gonzalez (1984) attest that when cold fluid is injected into a warmer reservoir, there is a tendency for the rock around the well to contract, which leads to the emergence of a region affected by thermoelastic stresses, which can reduce horizontal stresses locally. The authors claim that in cases of water injection in reservoirs, even moderately buried, the thermal effect can reduce the original stresses by hundreds of psi. A consequence of the stress reduction is the reduction of the bottomhole pressure necessary to induce hydraulic fracturing of the formation, which in this case is considered a thermally induced fracturing. Charlez et al (1996) associate the increase of the II (injectivity index) of a water injection well with the occurrence of thermal fracture. The authors state that an indication of the occurrence of thermal fracturing is the sudden increase in the injectivity of the wells after some time of cold fluid injection, even when the bottomhole pressure do not exceed the estimated or measured original fracture propagation pressure for the region.