bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Investigation of Geothermal Storage and Extraction Using Huff-N-Puff Wells
Authors: Wu Yuxing , Salehi Saeed , Karbalaeisaleh Fatemeh 
Published: September 2023

ABSTRACT
The subsurface geothermal energy storage system uses underground temperatures for energy extraction and storage. The energy is extracted by an injection-production-shut in procedure. Working fluids (i.e., water) are injected into the underground and heated by the subsurface high-temperature reservoir. Then, the fluids are extracted to the surface for thermal purposes, such as electricity generation and direct-use applications. This study establishes a parametric study using numerical simulation methods to comprehensively understand the influence of reservoir properties and operational factors on the geothermal energy storage system. A huff-n-puff well is modeled to simulate energy extraction and storage purposes. Water is injected for 8 hours, produced for 10 hours, and shut in for 6 hours. The reservoir is assumed to be a pure water reservoir (the only fluid in the reservoir is water). The total time for one cycle is 24 hours (a day). The performance of the well in 30 days is simulated. Effects of several reservoir properties and operational parameters such as formation temperature, heat capacity and thermal conductivity of formation, permeability, porosity, injected, and produced rates are evaluated. The results present that as formation porosity increases from 5% to 30%, energy in place grows 26.1%. The water recovery factor decreases from 0.52 to 0.087. Compared with vertical permeability, horizontal permeability has a much more significant influence. The formation temperature increases from 60 °C to 210 °C resulting in a 434% increase in the energy in place. Water recovery factor rises from −0.27 to 0.17 as the temperature from 60 °C to 90 °C, then remains constant (the negative value means under this condition the injected rate of water from the surface facilities is higher than its produced rate). Thermal conductivity has no important changes in energy extraction, while heat capacity affects the energy in place. When heat capacity is accelerated from 1.3×106 to 2.5×106 J/(m·day·°C), the total reservoir energy increases by 60%. Operation factors significantly influence the recovery factor and reservoir energy by changing the injected and produced rates.
Modeling Perforation Orientation and Hole Size Effects on Hydraulic Fracture Distribution in Horizontal Wells
Authors: Sinkov K. , Kresse O. , Hobbs B. , Shrivastava K. 
Published: September 2023

ABSTRACT
A modeling study was conducted with the objective of investigating the effects of perforation design and perforation size consistency on treatment allocation in multicluster limited entry treatments. The numerical model couples an advanced wellbore and perforation flow simulator and a well-established fracture simulator, which enables realistic modeling of complex perforation designs and pumping schedules. The study demonstrates that low variability of entry hole dimension among perforations is an important prerequisite for optimization of multicluster treatment uniformity. Variation of initial diameter due to noncentralized perforation gun positioning is shown to cause preferential slurry distribution to larger perforations, faster erosion, and further shift of distribution to the most eroded perforations. Erosion of perforations receiving a major fraction of proppant reduces the pressure drop for the entire cluster and thus eliminates the positive effect of higher friction on proppant distribution along the stage. Perforation designs with consistent initial perforation sizes, e.g., achieved using zero-phasing perforation guns, are shown to result in more uniform treatment distribution among clusters.

INTRODUCTION & MODEL DESCRIPTION
The completion efficiency and production of horizontal multistage hydraulically fractured wells are strongly affected by the uniformity of slurry and proppant distribution among multiple simultaneously stimulated perforation clusters within a stage. Depending on the fracturing treatment design, various factors related to either reservoir properties and their variability (Kresse et al., 2023) or peculiarities of proppant transport in a well and perforation tunnels can determine treatment distribution regularity. In the case of limited entry designs, commonly employed to improve treatment distribution among multiple intervals, perforation friction is used to mitigate variation of slurry flow rates to different clusters. High values of perforation friction are usually achieved by reducing the number of perforations (Somanchi et al., 2017) and, accordingly, are more sensitive to inconsistencies in the dimensions of the fewer entry holes. Moreover, the reduction in the number of holes leads to an increased amount of proppant pumped through the individual perforation and facilitates erosion, which can diminish the positive effect of initially high friction and aggravate treatment distribution nonuniformity (Thiessen et al., 2021).
Characterization of Fracture Propagation in Granite Under Uniaxial Compression Test Through Digital Image Processing and Discrete Element Method
Authors: He Changdi , Mishra Brijes 
Published: September 2023

ABSTRACT
This study utilized digital image processing (DIP) and discrete element method (DEM) to explore the correlation between mineralogy and fracture propagation in granite. The study concludes that an increase in the content of quartz and feldspar leads to a gradual increase in the uniaxial compressive strength (UCS) value of granite. However, the UCS value of granite undergoes a significant decline with increasing mica content. Additionally, the presence of quartz intensifies the brittleness of granite, while feldspar enhances the ductility of granite. In the isotropic model, fractures tend to initiate from stress concentration points and propagate during the UCS test, causing further stress concentration due to the creation of high-stress zones by the crack tip. In the anisotropic model, fractures usually occur in areas where quartz and feldspar are more concentrated because of a higher likelihood of stress concentration in those regions. However, mica agglomerations are not susceptible to stress concentrations due to their low strength and high toughness, which serve as a buffer.

INTRODUCTION
Granite is commonly utilized as a host rock for various underground engineering projects such as radioactive waste disposal, deep mining, and enhanced geothermal systems (EGS)(Zhu et al., 2021; Kumari et al., 2017). Nonetheless, the presence of fractures in granite can have varying effects on these projects. In the case of radioactive waste disposal, fractures can compromise the integrity of the repository by providing pathways for radioactive material leakage into the surrounding environment (Jia et al., 2022; Zhao et al., 2022a). Moreover, in deep mining, fractures can pose a significant hazard to miners as they can destabilize the rock mass, leading to rockfalls and collapses that may endanger their lives (Zhao et al., 2022b). Conversely, fractures in granite play a crucial role in EGS, as they facilitate fluid flow and heat transfer. The distribution and connectivity of fractures can impact the efficiency of EGS by affecting the flow of fluid through the reservoir (Zhong et al., 2022).
Development of Multiphase Flow Simulation Method in DEM Under a Fixed-Grain Condition
Authors: Dai Q. , Meng Y. , Duan K. , Kwok C. Y. 
Published: September 2023

ABSTRACT
Understanding multiphase flow mechanisms in porous media is vital for many engineering practices, such as geo-logical carbon sequestration. Existing numerical models that use the explicit pressure-solving scheme can only advance multiphase flow with a small timestep. None of them manages fast fluid transport due to a stability issue limiting timestep selection. This paper focuses on developing a fluid flow model that can quickly and efficiently capture fluid–fluid displacement patterns. We incorporate the implicit finite volume approach that is unconditionally stable to transport fluid with a remarkable timestep. To enhance interface–motion capture under various capillary number and viscosity ratio combinations, we set a flow front advancement criterion to reduce timestep when the injected fluid invades beyond front–line pores. Additionally, we update the flow front, pore pressure, and capillary entry pressure at every timestep to reveal more flow pattern details. We validate the model through a Darcy flow test and a fluid injection test based on existing Hele–Shaw tests. Numerical results agree well with the analytical solutions and experimental observations, confirming that the developed model is reliable for analyzing fluid migration problems and evaluating dynamic multiphase flow interactions in porous media.

INTRODUCTION
Geological CO2 sequestration is a crucial strategy for achieving carbon neutrality that stores greenhouse gas in geological formations, such as deep saline aquifers and depleted oil/gas reservoirs (Bradshaw et al., 2007; Bachu, 2008). Understanding how the injected CO2 migrates in geological media is vital to ensure successful CO2 geological storage. The injected CO2 will build up pore pressure and replace the existing pore fluid, remarkably altering the material properties (Sun et al., 2016) and pore structure (Yu et al., 2019). The pressure build-up during the injection process may trigger disasters, such as fault reactivation (White et al., 2014) and even earthquakes (Zoback and Gorelick, 2012), leading to CO2 leakage. To optimize CO2 injectivity and storage safety, it is thus essential to study multiphase flow mechanisms of fluid injection in porous media.
Three-Dimensional Salt-Pillar Equations and Their Applications to Industry
Authors: Belzer B. E. , Gupta N. 
Published: September 2023

ABSTRACT
Salt-pillar equations were developed over 25 years ago to assist with mine design. Pillar design is important for salt mines because the pillar size influences convergence of underground drifts with equipment clearance and headroom constraints, subsidence at the surface, and functional life of ground support. Current methodologies for salt-pillar design include using numerical-modeling techniques and salt-pillar-design equations as a method for estimating stresses and deformation rates. In this paper, three-dimensional simulations of square and rectangular salt pillars were performed, and the results were compared to the estimates of stress conditions using the salt-pillar-design equations. The results were used to investigate if the same salt-pillar-design equations are still valid following advancements in numerical-modeling software and the constitutive behavior of salt. This paper (1) reviews the salt-pillar-design equations, (2) compares the estimated stress conditions using numerical-modeling methods with the salt-pillar-design equations, and (3) discusses applications for the use of salt-pillar-design equations to salt mine design.

INTRODUCTION
The room and pillar size play a crucial role in the viability of an underground mine. Even for extensive mineral resource mines such as salt, pillar design influences the roof-to-floor convergence rate, stability of the salt back and nonsalt units, and accessibility period of mine workings. Unlike hard rock or coal mines, time-dependent deformational behavior of salt increases the pillar design complexity in underground salt mines. With technological advancement and laboratory creep tests on salt specimens, site-specific creep laws can be determined, and sophisticated numerical models can be developed to predict the room-and-pillar response over a specified period.
Van Sambeek (1996) presented that the simple pillar-design equations for salt pillars can reproduce the results of extensive numerical models, such as stress conditions in salt pillars. The premise of the Van Sambeek salt-pillar-design equations is that the average values of the vertical stress, the two horizontal stresses (as compared to their actual distributions), and the corresponding deviatoric of those average stresses are adequate to estimate the pillar's creep behavior and structural stability. Therefore, the salt-pillar-design equations relate the stress averages to the shape of the pillar in terms of its height-to-width (H:W) and height-to-length (H:L) ratios.
Study on the Generalized Zhang-Zhu Strength Criterion Considering Different Loading Paths of True Triaxial Tests
Authors: Zhang Q. , Shen Y. X. , Wang M. H. , Wang X. J. , Li X. J. 
Published: September 2023

ABSTRACT
Rocks in true triaxial stress states (σ1&gt; σ2&gt; σ3) have received much attention with the construction of deep underground engineering. True triaxial tests accurately reflect the triaxial stress state of rocks and have been widely used in the developments and validations of the three-dimensional strength criteria. Different loading paths are arranged to assess the deformation and failure properties of rocks as the development of true triaxial tests. In this study, the loading paths of the true triaxial tests are summarized as the traditional loading path, Lode angle loading path, and mean stress loading path. The ratios of σ2 and σ3, Lode angle, and mean stress can be regarded as invariants for three loading paths, respectively. The alternative expressions of the generalized Zhang-Zhu strength criterion of different loading paths are obtained by combining the three invariants. The expressions incorporate the properties of three loading paths to represent the correlations between σ1 and σ3 in simple forms. Finally, the typical rock data of three loading paths are collected to investigate the characteristics of the triaxial test data and the alternative expressions. The results show that the alternative expressions accurately predict the rock strength for different loading paths and reflect the effect of invariants of the loading path on rock strength. Adoption of three loading paths is discussed, and it is noted that the appropriate loading paths should be selected according to laboratory conditions and research priorities.

INTRODUCTION
With the extensive utilization of underground space, mineral, and environmental resources, the construction of deep underground engineering has been rapidly developed (Xie et al., 2017). Deep underground engineering is confronted with a complex environment such as high ground stress, high ground temperature, and strong disturbance (He et al., 2005; Qian and Zhou, 2018; Zhu et al., 2019). The mechanical behavior of deep rock is significantly different from that of shallow rock. Numerous studies indicated that the stress of deep rock presents a three-dimensional (3D) unequal characteristic (σ1&gt;σ2&gt;σ3) (Haimson and Rudnicki, 2010; Zhu et al., 2013; Zhu et al., 2017; Cai et al., 2021), which is defined as true triaxial stress state. Therefore, the strength characteristics of the rock cannot be effectively reflected by conventional triaxial tests (σ1&gt;σ2=σ3) because the effect of σ2 is neglected (Zhang et al., 2013; Ma et al., 2017; Lu et al., 2020). It is important to study the mechanical properties of rock under true triaxial stress states.
A Semi-Analytical Model for Poro-Thermo-Elastic Stresses by Injection in a Finite-Height Layer
Authors: Fokker P. A. , Buijze L. , Wassing B. B. T. 
Published: September 2023

ABSTRACT
The injection of fluids in geothermal energy, as well as in CCS, is accompanied by changes in stresses due to the reduced temperatures and elevated pressures. This can result in unwanted hydraulic fracturing and fault reactivation. We have developed a fast, semi-analytic tool to evaluate these changes and their consequences in terms of risk measures like fault reactivation probability, fracturing potential, and their spatial distribution. The tool has been designed for radially symmetric scenarios, which facilitated the use of an analytical approach. Pressure and temperature are calculated based on advection in the injection layers and diffusion in the bounding layers. The induced stresses are calculated based on these fields, using expressions for finite cylinders with elevated temperatures or pressures. Together with the virgin stress field, this provides input for the risk measures. With the semi-analytic approach, calculation times are limited and stochastic analyses are possible. We show how the shape of the disturbed zone in the injection layer and the amount of temperature and pressure diffusion into the bounding layers critically affect the stress field and the associated risk measures. We demonstrate how the tool can be applied to a geothermal injection well and to a CCS prospect, and how it helps in deciding what to target with data gathering.

INTRODUCTION
The transition to a sustainable energy economy poses multiple new challenges. Many of them are related to new ways of using the subsurface. As an example, the utilization of geothermal energy through an injection – production well doublet can only be safeguarded if the produced water is injected in the reservoir from where it was produced and does not leak away. For the storage of CO2 in CCS (Carbon Capture and Storage), it is also of prime importance that the carbon remains within the intended reservoir. Both applications thus require that the integrity of bounding layers is not breached.
Induced seismicity can also be an unwanted result of injection operations. Several geothermal field trials have been suspended or terminated because of unwanted induced earthquakes (Grigoli et al., 2018; Vörös & Baisch, 2022; Zang et al., 2014). At the same time, fault reactivation is sometimes required to ensure adequate transmissivity, e.g. in Enhanced Geothermal Systems (Majer et al., 2007). The concept of soft stimulation was introduced as a means of optimization of these two requirements (Hofmann et al., 2019). For balanced injection into porous sandstone formations seismicity has not yet been observed. However, because the number of projects is still small and duration of operations is short, it is important to assess fault reactivation potential for these types of operations as well.
Sand Production Prediction Based on Deep Learning and BP Neural Network
Authors: Jing Hongtao , Tu Zhixiong , Zhang Bao , Zeng Nu , Yi Jun , Yu Xiaotong , Si Xiang , Liu Suo , Xu Taiping 
Published: September 2023

ABSTRACT
Deep learning can better simulate highly nonlinear engineering problems through training adjustment, and has good practicability for predicting invisible data. BP Neural Network (BPNN) is a widely used deep learning algorithm, and strengthens the accuracy of developing training models through feedback adjustment to increase the accuracy of target prediction. This work considers the similar lithology characteristics in the same block, the sand production profile of a single production well is first predicted by using empirical formulas and logging data, and further the logging data and sand production profile are trained by back-propagating to continuously adjust the weights and values of BPNN. Finally, one develops a sand production prediction model based on deep learning and the BP neural network algorithm, and uses the model to predict the potential of sand production of other production wells in the same block. The prediction results (training set) of the BP neural network algorithm are in good agreement with the traditional empirical formula (testing set), and the goodness of fit reaches 0.9 or more. Therefore, it increases the confidence in the proposed sand production prediction model based on deep learning and the BPNN algorithm to improve the early warning of the risks of sand production.

INTRODUCTION
Both the poorly consolidated sandstone reservoirs with lower strength and high-pressure gas wells with a higher production speed are potential candidates for severe sand production. Therefore, accurately predicting sand production plays a role in the choice of sand control methods. The core samples are often restricted to enough obtained, and thus it fails to get a sufficient amount of test data related to the rock mechanics and strength parameters in a laboratory, such that a poor prediction of the sand production is made. However, a good choice that the logging data combines with the classical statistical empirical formulas, such as combined elastic modulus, sand production index (Chen et al.,2008), and Schlumberger sand production index (Tixier et al.,1975), can quickly provide the sand production profile of a single well, and thus sand production profile is convenient for engineers to capture the potential formation section of sand production in oil and gas wells, and helps engineers to timely adjust production allocation and optimize sand control methods.
Theoretical and Modelling Insights into Rate-Dependent Sorptive Viscoelasticity
Authors: Siddiqui M. A. Q. , Regenauer-Lieb K. , Roshan H. 
Published: September 2023

ABSTRACT
Recent thermodynamics-based constitutive modelling has enabled robust formulations for complex coupled mechanical, hydraulic and chemical interactions. Despite such advances, constitutive modelling of fractured sorptive media with complex mechanical behaviour has attracted little attention. This study presents a new sorptive poro-viscoelastic model for fractured rocks specifically integrating the rate-dependent viscous flow into the coupled fracture fluid flow and matrix gas desorption processes using the two-potential framework, mixture theory, and continuum mechanics. The proposed dissipative viscoelastic strain rate evolution law is governed by the applied stress variable and the amount of adsorbed gas in the matrix pores. The model is exemplified through the simulation of gas production from a sorptive shale formation. The numerical results show that poro-viscoelasticity becomes dominant at late times of production when pore pressure and desorption fronts have progressed significantly. It is also revealed that time-dependent stress accumulation can reach high magnitudes relatively early in the production phase which can cause fracture closure risking impedance to further gas production. Neglecting viscoelastic multiphysics effects in the modelling of fractured sorptive rocks can reduce accuracy of the predicted production data. In addition, the contribution of desorption-induced viscoelasticity to bulk rock deformation may be substantial in shales and other highly adsorbing rocks and may be the key to explaining some of the complexities encountered during hydraulic fracturing operations such as shale water loss and fracture closures.

INTRODUCTION
Shale formations are among the most abundant and widely distributed geological formations on earth, with enormous potential as a source of energy. Understanding the mechanical behavior of shales is essential for optimizing the hydraulic fracturing and gas production processes and the long-term stability of shale formations (Algazlan et al., 2022; Huang & Ghassemi, 2013; Siddiqui et al., 2022). The viscoelasticity and sorption behavior of shales are critical parameters that influence the stress-strain response of shale rocks, particularly under dynamic loading conditions as experience during gas production. In this context, a constitutive model that captures the sorptive viscoelasticity of shales can provide valuable insights into the mechanical response of shale formations.