bluuebunny/crossref_metadata_2025_split huggingface dataset:
EDFM-AI for Calibration of Hydraulic and Natural Fracture Geometry
Authors: Liu Chuxi , Xie Hongbing , Mao Zhenyu , Yu Wei , Li Ning , Gong Yiwen , Leines Joseph , Miao Jijun , Sepehrnoori Kamy 
Published: September 2023

ABSTRACT
Due to highly uncertain nature of unconventional reservoirs and difficult monitoring of the engineering effectiveness, a reliable, accurate, and efficient reservoir model calibration workflow is essential to help operators understand/plan their assets. In this paper, a collection of the non-intrusive EDFM (Embedded Discrete Fracture Model), AI (artificial intelligence), and an unconventional-targeting in-house reservoir simulator URSim is built to perform automatic history matching and uncertainty calibration of hydraulic and natural fractures (abbreviated as EDFM-AI). By implementing the proposed workflow, highly uncertain parameters, such as hydraulic fracture half-length, height, conductivity, closure coefficient, etc. are easily characterized. To validate the robustness of the proposed workflow, especially on the level of simultaneous multi-well calibration, a field-scale shale gas reservoir model is prepared with 3 horizontal wells and 200 hydraulic fractures for each well. Known set of hydraulic fracture parameters are inputted, constant gas flow rates are the well constraints, and the simulation outputs are defined as benchmark data. The history matching results showed high accuracy matches. More importantly, the maximum error between calibrated P50 and true value is only 6.8%. This novel EDFM-AI workflow sheds light on post-frac evaluation and completion optimization in unconventional resources.

INTRODUCTION
Current unconventional reservoir developments are characterized as fast-paced, real-time, and multi-well (pad-wise drilling). Many operators can drill and completion more than 100 unconventional horizontal wells per year. Under this scenario, it is crucial for operators to understand the effectiveness of hydraulic fracturing. Multitude methodologies/studies have been dedicated to study the man-made hydraulic fractures. These include fracturing simulation models (Wan et al., 2020; Weijermars et al., 2020; Leem et al., 2022), experimental methods (Magsipoc et al., 2020; Wei et al., 2021), and diagnostic technologies (Gutierrez et al., 2010; Ugueto et al., 2021; Wang et al., 2022). However, uncertainties associated with fracture geometries still remain as the most challenging problem in the unconventional oil/gas industry.
Finite Element Modeling of TBM Tunneling in Mixed-Face Ground Conditions
Authors: Witasse R. , Kashfi S. M. , Iman K. P. 
Published: September 2023

ABSTRACT
This article aims at demonstrating how the use of advanced numerical methods such as the Finite Element Method can provide a reliable prediction of the different ground formation behavior and development of structural forces during tunnel construction. It will particularly illustrate how the challenges associated with TBM excavation in mixed faced conditions could be efficiently dealt with using the finite element analysis. More specially detailed numerical analysis techniques for dealing with the construction of closed twin tunnels in mixed face conditions will be provided using the FEA software PLAXIS 2D.

INTRODUCTION
With the ongoing advancement of Tunnel Boring Machine (TBM) capabilities, the ability to tunnel through mixed face conditions has been improved dramatically and the risks have been reduced significantly. Still, mixed-face ground encountered in TBM tunneling presents great design and construction challenges for the tunnel engineers. From a geological viewpoint, the mixed-face condition is defined as the simultaneous occurrence of two or more geological formations with remarkably different properties in rock/soil mechanics, engineering geology as well as hydrogeology, or the same geological formation with different weathering grades. This paper aims at demonstrating how the use of advanced numerical methods such as the Finite Element Method can provide a reliable prediction of the different ground formation behavior along with development of structural forces and remarkably help geotechnical engineers to reach cost-effective and reliable tunnel design and construction.
One of the first challenges is the consideration of the specific in-situ stress conditions with a large variation of initial orthotropic stresses from one geological formation to the neighboring one with possible significant initial locked stress in certain rocky layers that must be accounted for. The soft soil at the top of the face and the hard rock at the bottom makes it difficult to maintain a proper face-support pressure and face stability, and increases the risk of excessive cutter wear, face collapse, sinkholes, or damage to surrounding structures. This is another challenge that should also be properly addressed. To avoid undesirable ground surface settlement as well as provide appropriate safety measures and limit impact on existing assets, tunnel engineers must also be able to reliably predict the amount of settlement under all given ground conditions. The ground movement around the excavated ground mass will lead to stress changes (arching) the extend of which will define the effective load on the tunnel lining and will greatly condition its design. The mixed-face ground conditions will also induce uneven loading on the segmental lining that must be accurately assessed with the proper consideration of segment-to-segment non-linear contact interaction.
Fully Coupled Near-Wellbore Multiphase Poromechanics Simulation for CO2 Storage
Authors: Huang J. , Hamon F. , Gazzola T. , Gross H. , Cusini M. , Settgast R. R. , White J. A. 
Published: September 2023

ABSTRACT
In geological CO2 storage operations, wellbore deformations and leakage pathways formations can occur around injection and abandoned wells subjected to high rates and long-term CO2 injection. To guide engineering design and prevent CO2 leakage risks, a full understanding of the underlying physics and robust numerical models are necessary to evaluate the response of underground formations in the near wellbore region and in the reservoir. In this study, a multi-scale and multi-physics open-source simulator (GEOS) is used to simulate multiphase flow and poromechanical deformations over time in three dimensions. The governing equations for mechanical deformations of the rock body and multiphase compositional fluid flow within the rock matrix are solved with a fully coupled finite element and finite volume approach. Simulation results are validated against multiple analytical solutions for multiphase flow and wellbore problems, thus demonstrating the accuracy of this advanced simulator. This work focuses on short-term processes in the vicinity of injection wells where stress evolutions, rock deformations and multiphase compositional flow and transport are simulated jointly to ensure wellbore stability and prevent damage. This fully coupled geomechanical model can simulate multiphase flow and any associated poromechanical effects within the CO2 storage site and in the surrounding formations. Such a large-scale, long-term, multi-physics simulation model is useful in many ways: it can guide operational decisions for CO2 injection, assess the containment potential and risks of a site, and analyze the wellbore stability and integrity during and after CO2 injection.

INTRODUCTION
Geological carbon sequestration (GCS) is a method to reduce atmospheric carbon concentration by storing vast amounts of CO2 in underground formations. The mechanical deformation of underground formations around CO2 injectors can lead to operational and geological hazards. If subjected to high rates and long-term CO2 injections, leakage pathways might be formed around abandoned wells and mega-faults (Nogues et al., 2011; Gan et al., 2021). Therefore, during and after CO2 storage operations, wellbore and caprock stability and integrity should not be compromised to mitigate the risk of CO2 leakage (Bachu and Bennion, 2009; Vilarrasa, 2014; Torsæter et al., 2017; Onishi et al., 2019).
Numerical Modeling of Seismic Wave Propagation in Mimicked Underground Mine Models
Authors: Mukhamedyarova Z. , Suzuki Morales K. , Suorineni F. , Madenova Y. 
Published: September 2023

ABSTRACT
Underground mines are going deeper worldwide with increasing production of mineral resources and decreasing ore grade, and this fact is creating challenging conditions. This fact makes the research into mine seismicity problem paramount. This manuscript focuses on the study of seismic wave propagation in a single material medium imitating the conditions found in underground mines. Understanding how waves propagate in a medium is fundamental to better interpret real-time information for accurate rockburst prediction. For this purpose, a numerical model is developed to represent results from laboratory experiments in which a signal of AE is transmitted through the material to measure the arrival time at different sensors located in the sample. The objective of the model is to better understand the physics of wave propagation and attenuation in the medium, which cannot be directly observed in a laboratory experiment. The model will be further used for other materials and geometries to study seismic wave propagation. The study considers two configurations: the first is a solid granite cube and the second is a solid granite cube with an empty hole in the middle. These configurations are modeled in FLAC3D. The main assumptions are that materials are elastic, and the signal's waveform is sinusoidal. The study results showed wave propagation within a sample and quantified differences between modeled configurations. The model will be further used for other materials and geometries to study seismic wave propagation.

INTRODUCTION
With increasing production and depletion of mineral resources, underground mines are going deeper worldwide (Feng et al., 2019). Moreover, there are geotechnical engineering projects such as tunnels and underground laboratories located in very deep areas with complicated geology and ground conditions (Jiang, Feng, Xiang, & Su, 2010; Zhang, Feng, Zhou, Qiu, & Wu, 2012). Factors controlling seismic activity in the mine are not equivalent to those controlling the volume of the damage caused by seismicity. High stress is not the only factor causing seismicity; in fact, not all highly stressed areas are amenable to seismicity. There is a strong correlation between areas with a considerable decline in the volume of stored energy and seismically active regions. A threefold analysis is needed for the assessment of potential energy release that responds to mining works and major components of the analysis are stress, energy and loading system. Some of the conditions to be satisfied with seismic energy release from the rockmass are that (a) applied stresses have to exceed the strength of the rockmass, (b) a considerable volume of energy needs to be stored and released, and (c) energy release must be in a short period to initiate the dynamic, non-linear response of the rockmass (Kaiser, McCreath, & Tannant, 1996).
Numerical Simulation of the Effects of Casing Eccentricity on Inclined Wellbore Integrity in Salt-Gypsum Formation
Authors: Liao Jianhua , Liu Nanxiang , Chen Xuyue , Yin Siyuan , Yang Qiqi , Wang Gan 
Published: September 2023

ABSTRACT
Protecting the integrity of the wellbore is a major challenge for the sustainable development of hydrocarbon resources in nitrate formation. In this paper, A numerical model for investigating the effects of casing eccentricity on inclined wellbore integrity in salt-gypsum formation is developed. The effects of creep time, eccentricity distance, cement sheath modulus of elasticity and internal casing pressure on wellbore stress were investigated using the finite element method. The results show that for a given eccentricity, the stress on the wellbore increases with creep time, affecting the integrity of the wellbore. At eccentric distances above 0.25R(the outer diameter of the cement sheath), the stress on the inner and outer walls of the cement sheath are higher than the ultimate strength of the cement sheath and damage occurs to the cement sheath. The increase in the modulus of elasticity of the cement sheath is effective at low eccentricity distances and destroys the cement sheath at high eccentricity distances. The increase in casing pressure is beneficial in protecting the integrity of the wellbore.

INTRODUCTION
The Salt Paste Formation is one of the most extensive formations covering hydrocarbon resources in the world. The typical creep nature of the salt formation leads to casing necking and deformation during production and development, which affects the development of oil and gas fields. The main directions of research on casing damage in salt formation are: (1) Proposing block-specific creep models for salt formation through triaxial creep experiments and parameter fitting (Duan et al. 2013). (2) Using numerical simulation methods to study the effects of formation creep and other factors on casing stress (Yang et al. 2021).
Taheri et al. (2020) carried out triaxial creep experiments on rock samples from the Gachsaran Formation and obtained creep parameters that differed significantly from those of salt rocks from other areas. Ge et al. (2013) combined creep experiments on salt rocks to determine creep parameters and study the effect of casing wear on casing equivalent stress under creep conditions. Zhao et al. (2020) simulated the loading and unloading processes of the injection and pumping phase cycles to investigate the effect of loading waveforms on the creep-fatigue properties of rock salt.
Preliminary Laboratory Results of Irregularly Shaped Specimens Modeled After Irregularly Shaped Stone Pillars
Authors: Wedding Z. , Agioutantis Z. , Calnan J. 
Published: September 2023

ABSTRACT
Underground stone or hard rock mines typically employ the room-and-pillar mining method. Room-and-pillar mines are designed in traditional patterns with square or rectangular shaped pillars. This method is favorable because the symmetric pattern aids in optimizing mining operations. In active mines, deviations from the mine plan often result in irregularly shaped pillars. In older mines, which were designed when pillar design methodology was less developed, irregularly shaped pillars are more common than in current operations. The performance of hard rock pillars is primarily based on the pillar's stability factor and the width to height ratio, where the width is the smallest dimension of the rectangular base. The estimation of pillar strength in room-and-pillar stone mines has been studied by researchers and empirical relationships between traditional geometry (square and rectangular), and strength have been developed. Determining the strength of irregularly shaped pillars is integral to determining the pillar and regional stability. This paper presents preliminary laboratory results for specimens with irregular geometry that correspond to odd-shaped pillars and contrast to the strength of traditional specimens. Although a statistically significant difference between the UCS values measured for different specimen geometries was not established, preliminary results indicate that the intact core areas are of different dimensions.

INTRODUCTION
Underground stone or hard rock mines typically employ the room-and-pillar mining method. Room-and-pillar mines are designed in traditional patterns with square or rectangularly shaped pillars. This method is favorable because the symmetric pattern aids in optimizing mining operations. In active mines, deviations from the mine plan often result in irregularly shaped pillars.
The performance of stone or hard rock pillars is primarily based on the pillar's stability factor, which is a function of rock mass strength and the width-to-height ratio of the pillar. Width typically refers to the smallest dimension of the rectangular base. The estimation of pillar strength in room-and-pillar stone mines has been studied by researchers, and empirical relationships between traditional geometry (square and rectangular) and strength have been developed (Esterhuizen 2006; Esterhuizen et al., 2011; Lunder & Pakalnis, 1997; Martin & Maybee, 2000). Determining the strength of irregularly shaped pillars is integral to determining the pillar and regional stability, as the effective design of an underground pillar will maintain the local and global stability.
Crack Classification During Tunneling in Scale Model Testing Using Acoustic Emission
Authors: Gautam Pradeep K. , Gutierrez Marte , Wibisono Doandy Y. , Majumder Dipaloke 
Published: September 2023

ABSTRACT
Detecting the damaged precursor of deep tunnel excavations using crack classification is essential for ensuring structural safety and durability since the cracking mode of a crack (tensile or shear) is connected to a rockburst. Acoustic emission (AE) is related to the mechanisms of spalling (or slabbing) and rockburst phenomena. Acoustic emission is a passive nondestructive technique that allows for classifying cracking modes by analyzing AE signals using mostly empirical relationships between rise time of amplitude (RA) and average frequency (AF). Using AF-RA plots for different rocks, transition lines could be set up to show the difference between tensile and shear cracks. The main objective of this study is to investigate the impact of excavation on tunnel spalling observed in a scale model test on a brittle synthetic. The scale model test used a cubical specimen 300 mm × 300 mm × 300 mm in size with a 51-mm diameter tunnel drilled through one of the specimen faces. The tunnel length is approximately 150 mm or half of the specimen length. Six AE WSα sensors were employed during the excavation to record the accompanying AE signals during and after tunnel excavation. The locations of micro-or mesoscale fracturing were identified, and a comprehensive analysis of the intensity, temporal-spatial distribution, and quantitative investigation of the crack classification mechanisms was conducted. A frequency–amplitude relationship of AE signals in an excavation at each stage was proposed. The lower (60-120 kHz) and the higher (120-290 kHz) frequency ranges were revealed by the fast Fourier transformation (FFT) analysis of the AE signals. The AE signals have a high frequency and low amplitude when the specimens are under relatively low loading. But, as the load increases, the AE signals shift more towards a signature of high amplitude. It is observed that there are much higher amplitude and lower frequency events close to the specimen spalling failure. Hence, it directly reflects the lower frequency range of the shear cracks, and the higher frequency range is the tensile cracks that occurred. It was found that more than 74% of the AE signals were found below the transition line, and shear cracks dominated the surface during excavation.
Numerical Investigation of Hydraulic Fracture Propagation and Proppant Transport in Multi-Well Fracturing Stimulation
Authors: Yang P. , Zhang S. C. , Zou Y. S. , Ma X. F. , Li J. M. , Tian G. , Wang M. X. , Wang J. C. 
Published: September 2023

ABSTRACT
Multi-well fracturing techniques are beneficial to enhance stimulated reservoir volume and completion efficiency in unconventional oil and gas development. However, severe inter-well stress interference aggravates the uncertainty of fracture propagation and proppant transport, which poses challenges to the efficient development of reservoirs and the optimization of completing parameters. In this study, a fully coupled multi-well fracturing model considering both 3D propagating fracture and proppant transport is established based on the displacement discontinuity method and Eulerian-Eulerian approach, and the integrated model accounts for hydraulic fractures interaction (i.e., stress-shadow effects), gravitational proppant settling, proppant bridging, and the transition of fracturing fluids from Poiseuille to Darcy flow. The numerical results indicate that fracture propagation geometry under the multi-well fracturing completion is jointly affected by a variety of stress interference mechanisms, such as asymmetric fracture propagations due to the intense inter-well stress interference and the heel bias resulting from inter-stage stress interference. Because proppant transport capacity is mainly controlled by fracture geometry and width, proppant accumulation and bridging are easy to occur at smaller fracture widths, resulting in a limited proppant placement range on the whole. Through several scenarios designed to investigate the influence of key parameters, it is found that increasing well spacing and cluster spacing can reduce the inter-fracture stress interference, and promote the fracture lateral propagation and proppant distribution uniformly in each fracture. Increasing proppant concentration and reducing proppant size are effective methods to improve the propped fracture area. The obtained conclusions can be helpful to provide a better insight into fracture propagation and proppant transport in multi-well fracturing stimulation.

INTRODUCTION
In response to the demand for unconventional oil and gas development, well pads with hydraulic fracturing technology are widely used due to high efficiency and cost saving. Compared to single-well fracturing, the stress interference mechanism in multi-well fracturing is more complex, increasing the uncertainty of fracture propagation and proppant distribution. It further causes fracture-hit and premature tip screen-out, which seriously affects the stimulated volume and completion efficiency of well pads. Therefore, the research of fracture propagation geometry and proppant distribution in multi-well fracturing can contribute to the formation of hydraulic fractures with appropriate size, orientation, and propped area, which is indispensable for the economic development of unconventional reservoirs.