bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling of In-Situ Indentation Tests in the Framework of Material Point Method
Authors: Hu L. , Bhide R. , Nguyen W. , Butt D. , McLennan J. , Gadikota G. 
Published: September 2022

ABSTRACT:
This work presents numerical simulations of a series of In-situ TEM (Transmission Electron Microscopy) indentation tests using the framework of the Material Point Method (MPM). The selection of MPM is based on its robust capacity for handling large deformation problems which could otherwise be an arduous challenge for mesh-based numerical methods such as the finite element method due to issues with mesh tangling. In this work, the nanoparticles were represented with a collection of material points which carry all the information relevant to the material. The mechanical bonds between particles were simulated with cohesive elements. For simplicity, our current model is a 2D simulation and 3D modeling is pending. Furthermore, up-scaling was necessary to avoid excessively small-time steps. Comparison between the experimental data and the numerical results shows that the numerical modeling with MPM successfully simulates the failure processes manifested by the test specimens including both tensile and shear failure. Our simulation experience also suggests that using an implicit scheme in MPM could be a suitable and beneficial way for extending the application of this powerful numerical technique.

1. INTRODUCTION
Nanoindentation is a common and convenient experimental protocol to investigate near-surface mechanical properties, to depths of a few micrometers (Schuh, 2006; Oyen and Cook, 2009; Wheeler, 2015; Ma et al., 2020). The complementary application of in-situ transmission electron microscopy (TEM) enables the observation of deformation and creation of cracks at a micro scale (Minor et al., 2002; Sun et al., 2009; Wang et al., 2017). Unlike the considerable progress and extended applications of indentation tests for revealing the material behavior at nano/micro scale, numerical modeling of this technique in particulate agglomerates - at a micron scale - is relatively rare (Sajjad et al., 2020;). The biggest challenge arises from the large deformation relative to the particle size and the complicated interaction/movement between the particles. Commonly used mesh-based numerical methods such as the finite element method will fail due to mesh tangling if sophisticated and time-consuming mesh treatments are not employed. In this work, we simulated experimental in-situ TEM nanoindentation tests using the framework of the Material Point Method (MPM).
Transparent True-Triaxial Apparatus for Investigation of Hydraulic Fracture Branching
Authors: Li Wenfeng , Frash Luke P. , Carey J. William , Welch Nathan J. , Meng Meng , Viswanathan Hari S. 
Published: September 2022

ABSTRACT:
Hydraulic fracture branching has been observed in the laboratory and in the field. Our previous studies demonstrate that hydraulic fractures can branch into multiple directions for weak anisotropic in-situ stresses when intermedium injection rate and fluid viscosity are used. However, it is quantitatively unclear how the in-situ stress anisotropy affects hydraulic fracture branching. Understanding this question is important for the optimization of hydraulic fracture design for real-world applications because reservoirs are subject to varying degrees of in-situ stress anisotropy. To address this problem, we designed a transparent true triaxial (TTT) cell that allows us to investigate hydraulic fracture branching under different anisotropic stress conditions with distinct injection parameters and sample heterogeneity. This self-designed TTT cell has a transparent bottom window for us to record hydraulic fracture propagation in real-time. We completed a few benchmark experiments to verify the capability of the TTT cell for hydraulic fracturing tests. The most striking experimental observation is that hydraulic fractures can grow and curve in the direction inclined to the minimum principal stress. This crack growth can stop at some critical points, after which new hydraulic fractures are initiated in the direction normal to the minimum principal stress. The curvature-stop-reinitiation cycle repeats during hydraulic fracturing and generates crack strands. Our experimental finding agrees with the observations at the hydraulic fracturing test site. Therefore, the TTT cell offers unique capabilities for us to experimentally understand complex hydraulic fracture branching and stranding behavior in subsurface conditions.

1. INTRODUCTION
Hydraulic fracturing is a key technology that enables economic hydrocarbon production from low-permeability reservoirs (Smith and Montgomery, 2015). The same technology is also used to develop the Enhanced Geothermal System (EGS) for carbon-free geothermal energy extraction from the subsurface (Frash et al., 2014; Fu et al., 2021). Significant efforts have been made to advance our understanding of hydraulic fracture initiation and propagation in rock formations with anisotropic in-situ stresses (Haimson and Fairhurst, 1967; Detournay 2004; Fisher and Warpinski, 2012; Frash et al., 2015 & 2019). However, it remains unclear how do we effectively produce complex hydraulic fracture patterns in the subsurface which is very often subject to anisotropic in-situ stresses.
Study on External Water Pressure and Decompression Measures of Tunnel Concrete Lining
Authors: Deng J. Q. , Cui W. , Zhu Y. B. , Liu Y. , Du S. L. 
Published: September 2022

ABSTRACT:
Aiming at the problem of high external water pressure in deep buried tunnel, the maximum external water pressure of concrete lining caused by seepage field of surrounding rock is numerically studied, and the influence of consolidation grouting ring and drainage measures is studied based on the stable seepage analysis. When drainage holes are arranged in the tunnel, the underground water level around tunnel is funnel-shaped and its line is affected to some extent. The surface water level at tunnel location is about 100m lower than the original water level. The maximum pressure head outside consolidation grouting ring, shotcrete and secondary lining is about 490m, 260m and 255m, respectively. Considering the pressure reduction of drainage holes, the average external water pressure head of secondary lining is 170m. Without drainage holes, the underground water level around tunnel is funnel-shaped, but the range is small, and its line is basically not affected. The maximum pressure head outside consolidation grouting ring, shotcrete and secondary lining is about 1100m, 950m, 940m, respectively. Compared with the case with drainage holes, the maximum external water pressure head of the secondary lining increases by about 700m. The research can provide more scientific basis for designing and optimizing the lining structure and ensuring the safety of tunnel.

1. INTRODUCTION
Lining and surrounding rock are the main components of hydraulic tunnel, and the external water pressure is one of the main loads, as shown in Fig. 1. With respect to lining design, infiltration and external pore-water pressures are often one of the most important factors to be considered [1-4]. There are a lot of research on the problem of high external water to deal with the safety of lining in high external water pressure and the general treatment concept of "combination of blocking and drainage" is gradually formed. The composite lining is used to deal with the problem of high groundwater pressure and has been successfully applied in practical projects [5-11].
PDC Bit Wear Detection Based on YOLO V5 and OpenCV
Authors: Yang Donghan , Song Xianzhi , Wang Zheng , Pei Zhijun , Zhu Zhaopeng 
Published: September 2022

ABSTRACT:
In recent years, due to the remarkable advantage of increasing speed and reducing cost, PDC bits has occupied a dominant position in the oil bits market. In the drilling process, the bit will wear itself when breaking hard rock. When the abrasion reaches a certain degree, the drilling efficiency of the bit will be significantly reduced. Therefore, during the drilling process, it is necessary to change the bit in time to ensure the rate of penetration. The wear degree of cutters is the key factor affecting the efficiency of PDC bit. In order to quantitatively monitor the wear degree of cutters, computer image recognition is adopted to judge the bit abrasion level by analyzing the missing proportion of each cutter. The data set is made from the bit data used in Sichuan, China. We locate the position of each cutter to get coordinates based on YOLO v5, a deep learning algorithm of object detection. Then, we use OpenCV cropping the whole image with those coordinates to acquire every picture of cutters and perform noise reduction and smoothing. After that, the processed cutter images are used to calculate the missing area, and use the proportion to confirm the wear degree.

1. BACKGROUND
Nowadays, roller cone bits and PDC bits are the most commonly used bits in the field of oil drilling. With the continuous improvement of PDC bit cutter technology, PDC bit has become an important tool for drilling speed. Compared with traditional roller cone bits, PDC bits offer significant advantages in cost, rate of penetration and footage per bit when drilling formations, especially in deep and high-pressure wells.[1] Although PDC bits has high wear resistance, it’s inevitable that the PDC bits being worn out. If the bit abrasion reaches a certain degree, the drilling efficiency of the bit will be significantly reduced. Therefore, it is necessary to obtain the wear condition of the drill bit in time to ensure the drilling speed.[2]
Micro Model Establishment and Numerical Simulation of Supercritical CO2 Filtration in Porous Media of Shale Oil Reservoir
Authors: Ping Xie , Haizhu Wang 
Published: September 2022

ABSTRACT:
Supercritical CO2 fluid has the characteristics of low viscosity, easy diffusion, non-toxic and tasteless. It is considered as an ideal working fluid in the fracturing of unconventional reservoirs such as tight oil and gas and shale oil and gas. However, compared with water-based fracturing fluid, supercritical CO2 has very strong filtration. The filtration of supercritical CO2 in the fracturing process has an important impact on the fracturing effect and the design of surface construction parameters. In the past few years, many experimental and simulation studies have been carried out to understand the filtration of Sc-CO2 in dense and shale formations. Although great progress has been made in the macro modeling of unconventional reservoirs, there is still a lack of research on the numerical simulation of micro seepage law, especially the modeling method and numerical simulation of S c-CO2 micro filtration law in fractured shale oil reservoirs. Through python programming, a method for establishing the micro model of shale oil reservoir with discrete fracture network is proposed. Based on the established micro model, the numerical simulation is carried out by using OpenFOAM calculation software to verify the availability of the model and the feasibility of the method.

1. INTRODUCTION
The US energy information administration estimates that the world’s total shale oil reserves are 345 billion barrels, including 75 billion barrels in Russia, 58 billion barrels in the United States and 32 billion barrels in China. Shale oil and gas will be an important field for countries to tackle key problems in the future. Since the "shale gas revolution" in the United States, the shale oil and gas industry in the United States has developed vigorously and the shale oil production has increased rapidly. As of December 2019, shale oil production in seven major production areas in the United States, including Permian , Bakken and Eagle Ford, has exceeded 9 million barrels / day, accounting for 70% of the total crude oil production. In 2019, Saudi Arabia became the world’s largest producer of oil and gas, surpassing the United States in the global oil and gas market.
Impact of the Back-Stress Effect on Horizontal Stress Values Calculation in Hydraulic Fracturing Experiments
Authors: Novikova E. V. , Trimonova M. A. , Nachev V. A. , Dubinya N. V. 
Published: September 2022

ABSTRACT:
The study presents an analysis of the back-stress effect on precise determination of in-situ stresses in a model samples in laboratory experiments on hydraulic fracturing. Main stage of this study included the determination of the fracture closure pressure using standard methods and comparing this pressure with the minimum loads applied to the sample. The comparison showed the inequality of these values. To eliminate the identified discrepancy, it was proposed to take into account the back-stress effect. This stress occurs due to an increase in pore pressure when fluid is filtrated into the reservoir from a hydraulic fracture. It affects the walls of the fracture, contributing to its closure. The second part of the study was devoted to analysis of back-stress effect impact on estimation of maximum horizontal stress. In this work, we evaluated the influence of this effect on the determination of the minimum and maximum stresses in the medium in laboratory experiments on hydraulic fracturing. Some assumptions about how to account for back-stress in the calculation of minimum stresses were considered. It was found that taking into account the back-stress when calculating the horizontal stresses significantly reduces the difference between the calculated values and experimental data.

1. INTRODUCTION
The problem of boundary conditions estimation emerges often when dealing with reservoir geomechanics problems (Zoback, 2007). First of all, contrary to the classical problems of mathematical physics, determination of stress-strain state of rock masses cannot be carried out with boundary conditions postulated at real boundaries of the rock mass, as there are no distinct boundaries constraining the rock mass within a single domain (Mukhamediev, 2015). Information necessary for stress estimation can be obtained only at discrete points – from seismic events analysis or wellbore data. This paper is focused on the latter – the problem of using wellbore data to understand the in-situ stresses at rock mass via estimating stresses existing in the well vicinity.
Physical and Mechanical Performance of Oil Well Cement Systems Under Simulated Shale Oil In-Situ Conversion Condition
Authors: Li Hailong , Pang Xueyu , Chen Xiaorong , Zhang Jian 
Published: September 2022

ABSTRACT:
The strength of Portland cement material deteriorates sharply in the high-temperature environment under the shale oil in-situ conversion condition, which can reach up to 650 C. During this study, the high-temperature resistance of oil well cement modified by different grades and dosages of silica flour was investigated. The dosages of silica studied ranges from 40 % to 70 % BWOC; the silica particle size ranges from 6 μm to 53 μm; the exposure temperature includes 380 C, 500 C, 550 C, and 650 C, respectively. The physical and mechanical properties of set cement, including permeability, compressive strength, Young’s modulus and stress-strain characteristics, were evaluated before and after high-temperature treatments. The results show that silica-modified cement can maintain reasonably high compressive strength and Young’s modulus after exposure to 550 C for 7 days. The use of ultrafine silica flour (D50 = 6 μm) at high dosage (70% BWOC) seems to be most effective, which resulted in a system with an average compressive strength of 43 MPa and a gas permeability of 0.1 mD. However, the physical and mechanical properties of all systems deteriorated dramatically when the specimens were exposed to 650 C for 7 days. Thermogravimetry analysis revealed that decomposition of carbonate hydration products is the primary reason for oil well cement strength decline exposed to high temperature in dry condition.

1. INTRODUCTION
In recent years, with the gradually increasing demands for oil and gas resources, conventional oil and gas resources have been unable to meet human needs (Zou, 2015). The exploitation of shale oil & gas has attracted widespread attention from researchers and investors alike. Shale oil with different maturity levels varies in composition content and production methods. High-maturity shale oil is normally produced by horizontal drilling and multistage hydraulic fracturing, while low-maturity shale oil cannot be produced in this way (Zhao, 2020). Considering the large potential of low-maturity shale oil reserves, their effective exploitation has become an urgent problem (Zou, 2015). Field experiments have shown that underground in-situ heating can achieve large-scale development of low-maturity shale oil and reduce environmental pollution. The in-situ conversion of shale oil requires heating the formation temperature to 500 °C or higher and maintaining it for a long time (Ma, 2017), which may have irreversible effects on the long-term stability of cement sheath. Therefore, it is necessary to conduct corresponding simulation experiments to better understand the set cement’s physical and mechanical properties under shale oil in-situ conversion conditions.
A New Perspective for the Conception of Mechanical Earth Model Using Machine Learning in the Volve Field, Norwegian North Sea
Authors: Berrehal B. E. , Laalam A. , Chemmakh A. , Ouadi H. , Merzoug A. , Djezzar S. , Boualam A. 
Published: September 2022

ABSTRACT:
Building a mechanical earth model (MEM) is a challenging task. It requires an extensive collection of data such as logs and core data to build a reliable model. MEM can support decision-making and assuaging the risks linked to wellbore stability, saltwater disposal, CO2 sequestration, fault slippage and induced seismicity. Obtaining the data required to build MEM relies on several costly and time-consuming operations such as core sampling, laboratory analysis, various well logs and well testing. This is while there are instances where data is not available. Therefore, a question arises in regards to the possibility of computing the latter critical components in a relatively less demanding manner using drilling related data. According to the literature, there is a direct relationship between data measured during drilling and actual rock behavior. These relationships, although complex, can be mapped using the combined power of machine learning and data analysis, resulting in accurate real -time estimates during drilling. In this paper, we employ a versatile set of machine learning and deep learning models to accomplish the latter.

1. INTRODUCTION
The estimation of stress is a critical component in any geomechanics study. Stress estimation can be applied in several ways in the oil and gas industry. For instance, wellbore stability, where the stress concentrates around the wellbore. Fault stability and induced seismicity, the effect of depletion, the hydraulic fracturing growth and containment, and recently the fracture-driven interaction and poroelastic stress changes due to injection during storage (CO2 and water disposal wells) (Zoback, 2007)
There are several approaches for stress estimation documented in the literature. Zoback (2007) suggests the use of frictional limit theory calibrated to diagnostic fracture injection test (DFIT), mini frac, leak of the test (LOT), or Extended Leak off test (XLOT). Sayers et al. (2010) explained the process of estimating stress for an isotropic and an anisotropic medium from logs and core data. The process needs density and sonic logs and, from that, estimates four components (Ostadhassan, 2013):
• Overburden Stress
• Elastic properties (Young's modulus, Poisson's ratio, Biot Coefficient)
• Pore pressure
• Horizontal stresses (minimum horizontal stress and maximum horizontal stress)
Overburden stress is calculated by integrating the density log from surface to depth z. computing the latter is relatively simpler in regards to the remaining components. The logs calculation results in a dynamic property that needs to be calibrated to a static one using core laboratory experiments. A data that is expensive to get. The pore pressure can be estimated from drilling activity; however, in low permeability formations such as shales, estimating the pore pressure is complicated.
Permeability Changes of Damaged Rock Salt Adjacent to Inclusions of Different Stiffness
Authors: Anwar Ishtiaque , Stormont John C. , Mills Melissa M. , Matteo Edward N. 
Published: September 2022

ABSTRACT:
Rock salt is being considered as a medium for energy storage and radioactive waste disposal. A Disturbed Rock Zone (DRZ) develops in the immediate vicinity of excavations in rock salt, with an increase in permeability, which alters the migration of gases and liquids around the excavation. When creep occurs adjacent to a stiff inclusion such as a concrete plug, it is expected that the stress state near the inclusion will become more hydrostatic and less deviatoric, promoting healing (permeability reduction) of the DRZ. In this scoping study, we measured the permeability of DRZ rock salt with time adjacent to inclusions (plugs) of varying stiffness to determine how the healing of rock salt, as reflected in the permeability changes, is a function of the stress and time. Samples were created with three different inclusion materials in a central hole along the axis of a salt core: (i) very soft silicone sealant, (ii) sorel cement, and (iii) carbon steel. The measured permeabilities are corrected for the gas slippage effect. We observed that the permeability change is a function of the inclusion material. The stiffer the inclusion, the more rapidly the permeability reduces with time.

1. INTRODUCTION
Rock salt is being considered as a medium for energy storage and radioactive waste disposal (Schulze, Popp, & Kern, 2001; Tsang, Bernier, & Davies, 2005; Yang, Daemen, & Yin, 1999) due to its extremely low permeability and low porosity. During the construction and/or facility operations, a Disturbed Rock Zone (DRZ) or Excavation Damaged Zone (EDZ) develops in the immediate vicinity of the excavation, with an increase in permeability (Gevantman & Lorenz, 1981; Schulze et al., 2001; Tsang et al., 2005). The increased permeability of the DRZ alters the migration of gases and liquids near the excavation.
Due to the deviatoric stress state that develops around excavations, rock salt creeps. When creep occurs adjacent to a stiff inclusion such as a concrete plug, it is expected that the stress state near the inclusion will become more hydrostatic and less deviatoric, promoting self-healing (Gevantman & Lorenz, 1981; Yang et al., 1999) of the DRZ, including permeability reduction. Healing adjacent to a concrete plug would limit bypass of the plug through the DRZ and thus be conducive to establishing a more effective seal system.