bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of Enhancing Coalbed Methane Recovery by RF Heating with Small Spacing Well Pattern
Authors: Liu Rui , Dong Xuelin , Gao Deli 
Published: August 2024

ABSTRACT:
In recent years, electromagnetic (EM) heating excitation technology has been widely concerned in the exploitation of Coalbed methane (CBM). However, the heating volume of a single antenna in a vertical well is limited and cannot meet the needs of large-scale development. From the perspective of multi-well and multi-antenna, this paper establishes a mathematical model of radio frequency (RF) heating coupled with EM field and temperature field of small-spacing well pattern, comprehensively analyzes the average temperature and heating efficiency of coal seam heated by RF, reveals the influence law of different well types on the temperature distribution of coal seam, and conducts sensitivity analysis on heating power, well spacing and well pattern layout according to the characteristics of well pattern. The results show that triangular well pattern heating has higher heating efficiency and heating rate. Increasing the RF heating power can improve the heating rate and heating range of the coal seam, but too high power will form high temperatures near the wellbore, resulting in downhole equipment or wellbore integrity failure. On the whole, the spacing of heating wells has little effect on the average temperature of coal seam. The larger the spacing of wells in 5 ∼ 9 m, the larger the heating range, but the worse the superposition effect of temperature. Finally, according to the different well pattern layout schemes in the same reservoir, the optimal scheme is well pattern 1.

1. INTRODUCTION
CBM is a kind of unconventional gas in coal seams. Deep coal seam has the characteristics of low formation pressure, low permeability and weak gas saturation, which are the biggest challenges faced by coalbed gas exploitation (Gao et al., 2022). To overcome these challenges, engineers and researchers have proposed a number of methods, such as hydraulic fracturing, blasting, partial pyrolysis, solvent extraction, inert gas displacement, etc. (Guo et al., 2020). These methods can be divided into two categories: decompression and anti-reflection mechanisms. However, these approaches face environmental and economic challenges. In recent years, thermal stimulation technology has been widely concerned as an alternative method to increase natural gas production in unconventional reservoirs.
Experimental Research on Fracture Propagation of Multi-Well Pad Fracturing Based on Distributed Strain Sensing
Authors: Zhang B. , Guo T. K. , Chen M. , Xue L. R. , Zhang Y. H. , Hu Z. P. , Qu Z. Q. 
Published: August 2024

ABSTRACT:
The conventional fracturing mode faces some problems, such as the low complexity of artificial fracture and rapid production decline after fracturing. The multi-well pad fracturing is a crucial technology for effectively developing unconventional reservoirs such as shale and tight sandstone. However, serious interaction exists between fractures when multiple horizontal wells are fractured. Therefore, it is crucial to determine the fracture propagation mechanism in the multi-well pad fracturing. Additionally, the propagation of complex fractures makes it difficult for traditional fracturing monitoring and diagnosis methods to evaluate the hydraulic fracturing operation promptly and effectively. The distributed strain sensing (DSS) technology can evaluate the fracturing effect in real time, which is a hot monitoring technology with an extensive application prospect in horizontal well fracturing. This study combined the DSS with a large-scale (400 mm × 400 mm × 400 mm) true triaxial fracturing device to carry out a three horizontal well preliminary fracturing experiment for the heterogeneous sandstone. Results show that the hydraulic fracture (HF) mainly forms the transverse fracture perpendicular to the direction of the minimum horizontal principal stress (σh). The HF near the well usually crosses the gravel, while the HF tends to bypass the gravel or even be inhibited by the gravel far away from the well. The waterfall diagram of the optic fiber strain can monitor the HF propagation dynamics in real time. Once the HF hits the fiber, the apparent tensile strain can be generated. If the HF deviates from the σh direction, the tension strain will spread to both sides. Under the stress shadow, the later fracturing fracture is prone to extend outside the stress shadow region of the earlier fracturing fracture. The preferential fracturing of intermediate fracture is conducive to exploiting the reservoir resource between the two sides of fractures, so the middle-near-far fracturing method is superior to the far-near-middle fracturing method. This study can provide the reference and guidance for the design of multi-well pad fracturing in oil fields.
Sand Rate in Gas Flow
Authors: Papamichos E. , Varkas M. , Walle L. E. , Berntsen A. N. 
Published: August 2024

ABSTRACT:
An experimental study was conducted to investigate the effects of gas flow on sand production. We compared gas flow tests to tests with oil or water flow. In the tests, hollow cylinder Castlegate and Saltwash North sandstone specimens, initially wet or at ambient humidity conditions, were isotropically compressed under simultaneous fluid injection. We carried out both one-phase as well as two-phase flow experiments to simulate important processes encountered in gas fields, like water capillary flow or water-cut. The sand onset results showed that sand onset was delayed in the gas flow experiments. The delayed sand onset, i.e., higher sand onset stress, was related to water evaporation due to gas flow, termed flow-through drying, which strengthens the rock. The sand rate results showed that extensive drying of the rock after long periods of gas flow alters its sand rate behavior. It results in continuous sand production of mostly individual grains and small flakes, owing to low grain cohesion forces in the absence of pore water.

1. INTRODUCTION
Sand production has been a serious concern for the oil and gas industry. It is responsible for erosion of downhole equipment and the need to dispose polluted sand, wellbore instabilities and, in extreme cases, to loss of wells. Sand production, under certain conditions, can also be associated with positive effects on the productivity of a well due to higher applied drawdowns, hole enlargement and removal of the near well damaged zone. The research efforts focused primarily on sand production in oil and/or brine flow as compared to gas flow. However, sand production in gas producing fields has been receiving increasing attention.
Sand production in cemented formations necessitates the mechanical failure of the rock material. This failure occurs when the shear stresses increase above the plastic yielding of the material due to the stress concentration of the effective stress near a well. After mechanical failure, the hydrodynamic force exerted by the flowing fluid on the failed, plastified material leads to erosion and transport of the rock material from the well leaving breakouts behind.
Development and Validation of a New Wellbore Stability Prediction Model for Complex Reservoirs: Application to the Keshen Gas Field in the Tarim Basin
Authors: Liu Yingjun , Xian Chenggang , Zhang Hui , Yin Guoqing , Xu Ke , Wang Zhimin , Lai Shujun , Liang Jingrui , Qian Ziwei 
Published: August 2024

ABSTRACT:
The objective of this paper is to propose a new method for predicting the safe mud density window of drilling fluid in the Keshen gas field, located in the Tarim Basin. The study focuses on applying this method to analyze wellbore stability in the complex and high-pressure environment of the field. The new method incorporates the Mogi-Coulomb criterion, which considers intermediate stress as the shear failure criterion of the wellbore. Additionally, the method accounts for the shear breakdown of rock when calculating the fracture pressure. It predicts the shear slip of the reservoir's weak surface using the Jaeger criterion. Furthermore, it takes into account the weak surface of drilling fluid invasion when calculating the tensile failure of the wellbore. The application of wellbore stability analysis in Well A reveals that the dislocation of natural fractures and the tensile fracture after the invasion of drilling fluid are significant factors contributing to wellbore instability, such as chipping and lost circulation, particularly in formations with developed natural fractures. In the case of a strike-slip stress field, shear sliding is more likely to occur when the fluid invades the crack or weak surface, as opposed to tensile failure. Based on the prediction results of the new method, the mechanism of wellbore instability is interpreted, and engineering countermeasures are proposed to mitigate the risk of wellbore instability.

1. INTRODUCTION
The Keshen gas field in Tarim Basin poses significant challenges due to its complex structure, high temperature, high pressure, complicated stress state, and developed natural fractures. These factors contribute to issues such as wellbore instability, a high accident rate, and prolonged drilling periods (Zhang et al., 2015; Cai et al., 2019; Zhu et al., 2014). The primary cause of wellbore instability lies in the disruption of the original mechanical equilibrium near the wellbore, leading to the redistribution and concentration of stress that exceeds the rock's strength once the drill bit penetrates the formation (Nelson et al., 2005; Abbas et al., 2019). The most common manifestations of wellbore instability are collapse and leakage. However, proactive determination of critical mud weights can often mitigate these drilling issues. To achieve this, a constitutive model is employed to estimate the stresses surrounding the wellbore and is complemented by failure criterions. Thus, establishing an accurate and reliable safe mud weights window is of utmost importance.
A Proposed Framework to Estimate Pillar Strength in Room-And-Pillar Hard Rock Mines
Authors: Dzimunya N. Z. , Fujii Y. 
Published: August 2024

ABSTRACT:
Pillar strength determination is a fundamental aspect of room-and-pillar mine design. Pillars are left between excavated rooms to maintain stability by restraining the hanging wall. In a typical mining environment, pillars of different rock mass conditions and geological characteristics are cut, resulting in variations in pillar strength. This is because pillars are highly anisotropic and cannot always be formed according to design dimensions. Consequently, unstable pillars may be present, requiring site-specific calibrated methods for ongoing monitoring and strength estimation. Pillar strength determination is typically accomplished using empirical formulae or numerical modelling. Although several numerical codes are available, mine sites still rely on empirical approaches despite their well-known limitations. Empirical methods are popular in the mining industry due to their simplicity. However, it is widely acknowledged that these methods can only be effective within the boundaries of their database and the specific problem scale for which they were designed. In contrast, continual monitoring of pillars and practical experience can enhance pillar strength evaluation. This work briefly describes pillar conditions at a case study mining operation. Additionally, a framework is proposed to estimate pillar strength based on ongoing pillar mapping, risk management decision making, numerical modeling, and analytical hierarchy process.

1. INTRODUCTION
The room-and-pillar mining method is one of the most vital underground ore extraction methods in practice today. In this method, pillars are systematically left in situ to support the overburden weight of the overlying rock mass. If the rooms and pillars are not designed carefully, it can compromise safety or lead to sterilization of the ore reserves.
Designing non-yield pillar systems for shallow hard rock room-and-pillar mines has always been a challenging task. It is important to know the stress distribution in the pillar and the strength of the pillar so that a sound design be produced. Due to the significance of these parameters, extensive research has been conducted on the strength of pillars in hard rocks. However, despite the numerous research outcomes, pillar failures still occur in underground room-and-pillar mines. The literature contains documented examples of such failures and their consequences (Esterhuizen et al., 2006, 2019; Malan, 2012; Ozbay et al., 1995).
Real-Time Prediction of Potential Hazard Area in Seville's During Underground Excavation with EPB
Authors: Bahri Maziyar , Düzgün Sebnem , Mascort-Albea Emilio J. , Romero-Hernández Rocío 
Published: August 2024

ABSTRACT:
One of the main challenges in geotechnical engineering involves addressing hazardous areas on the ground surface when conducting underground excavation using Earth Pressure Balance (EPB) in urban areas, particularly those with historical buildings. Given Seville's status as a historic city with ongoing underground metro construction, it is imperative for the city to thoroughly analyze and anticipate any potential hazards that may arise from the excavation process. This study aims to analyze and predict the potential hazard area during the real-time excavation with EPB based on a dataset that is generated in FLAC3D. This dataset contains 100-time steps of underground excavation and 87,034,800 entries. The first 80-time steps of excavation are considered training data, and the last 20 steps of excavation are considered test data. For predicting potential hazard areas, a modified Long Short-Term Memory (LSTM) architecture is employed, with an adjusting threshold for the ground displacement hazard specific to Seville. Consequently, the threshold was systematically modified, ranging from 0.5 to 10 cm. The area under the curve (AUC) values for the 1 and 2 cm thresholds are 0.937 and 0.939, respectively. This finding suggests that this study provides a useful framework for identifying potential risks caused by EPB in Seville.

1. INTRODUCTION
Given the rapid expansion of cities in the 21st century, it is crucial for them to expedite the development of their transportation systems in order to keep up with their increasing demands. Expanding the transportation infrastructure can be achieved by increasing the number of underground tunnels and metros. Nevertheless, excavating more underground tunnels may result in heightened surface displacement and the possibility of harm to buildings (Duranton & Puga, 2013). Controlling ground movements in underground excavation activities is crucial to prevent any potential damage to buildings and structures. Consequently, various studies have been conducted to control these movements using empirical equations, numerical models, and machine learning methods.
A Novel Model for Evaluating Temporary Plugging Effectiveness Between Clusters in Shale Gas Horizontal Wells
Authors: He Le , Zhan Li , Qian Bin , Guan Bin , Ren Yong , Chen Mingzhong , Qu Jianfeng , Liu Yuhao , Zou Longqing , Zhang Yao 
Published: August 2024

ABSTRACT:
In order to evaluate the temporary plugging effectiveness between clusters, this study proposes a novel model to calculate perforation opening ratio before and after the introduction of temporary plugging materials. The model is based on the fracturing operation curve and takes into account the perforations erosive effects. Taking Well A and Well B in the Weiyuan area as examples. The research results indicate the following: before the introduction of temporary plugging materials, the perforation opening ratio ranges from 35.1% to 42.5%, after the introduction of temporary plugging materials, the perforation plugging ratio ranges from 30.5% to 46.2%, following the dissolution of temporary plugging materials, the perforation opening ratio ranges from 76.9% to 83.5%. At a displacement of 14 m3/min with a single plugging operation and 12 m3/min with two consecutive plugging operations, the perforation opening ratios are 79.7% and 82.9%, respectively. The perforation opening ratios are comparable under both conditions, therefore, increasing the displacement and reducing the frequency of temporary plugging operations can effectively increase the perforation opening ratio. The model has been successfully applied in more than ten times in the Weiyuan area, providing robust support for the evaluation of temporary plugging effectiveness between clusters.

1. INTRODUCTION
The multi-section and multi-cluster hydraulic fracturing technique in horizontal wells is a crucial technology for shale gas extraction (Zargari et al., 2010; Xu et al 2018) However, factors such as reservoir heterogeneity and stress-shadowing lead to the partial opening of perforation clusters, resulting in incomplete stimulation of the horizontal section (Cramer et al., 2019). The key technology to address these issues is the temporary plugging and diversion (TPDF) fracturing technique. This technique involves introducing temporary plugging materials to plug the already-opened perforations, forcing subsequent fluids to redirect into unopened perforations, creating new fractures, and achieving thorough stimulation of the horizontal section. (Ataur et al., 2017; Leonid et al., 2018; Cyrille et al., 2020).
Finite Element Modeling of Frictional Contact Between a Blunt Tool and Rock with Anisotropic Damage
Authors: Zhou Yaneng , Voyiadjis George Z. 
Published: August 2024

ABSTRACT:
The mechanism is investigated for frictional contact between a wear flat and rocks. A brief review focuses on the governing parameters of frictional contact on different types of rocks. Anisotropic damage is taken into account using an anisotropic elasto-plastic-damage model, as demonstrated by a single-element test in uniaxial compression. Anisotropic damage is controlled by a compressive damage coefficient ζ, which can be interpreted as the ratio of axial damage to lateral damage in a special case of uniaxial compression. Tool-rock frictional contact is investigated using a finite element model consisting of a slightly inclined tool and a quasi-brittle rock with induced anisotropic damage. The nature of frictional contact is predominantly governed by three dimensionless parameters: the elastoplastic parameter η, the brittleness number ξ, and the anisotropic compressive damage coefficient ζ. The dimensionless average contact stress (equation) increases with the elastoplastic parameter η, and then slightly varies before leveling off. The contact stress (equation) generally decreases with an increase in the brittleness number ξ. Additionally, the contact stress (equation) increases with a decrease in the damage coefficient ζ from isotropic to anisotropic damage. The numerical results of (equation) are generally consistent with typical experimental results.

1 INTRODUCTION
Tool-rock interactions have important applications in various subsurface operations, such as hydrocarbon production, geothermal exploration, and carbon sequestration (DePaolo and Cole, 2013; Phelan et al., 2022; Li et al., 2023). Different types of tool-rock interactions have been extensively studied from various perspectives, including tool wear, rock failure modes, and material characterization. A wear process is influenced by three components, including the cutting tool, rock properties, and interfacial properties (Hamzaban et al., 2023). The wear of tools increases with increasing applied loads and travel distances, resulting in reduced cutting efficiency (Rostami et al., 2014; Zhou et al., 2017). Different failure modes in rock cutting have been revealed through extensive laboratory tests with both sharp and blunt cutters (Rostamsowlat et al., 2019; Zhang et al., 2022). The mechanisms of tool-rock frictional contact have been investigated using various constitutive models for rocks in numerical modeling (Zhou and Detournay, 2014; Voyiadjis and Zhou, 2019; Zhou and Voyiadjis, 2021). Tool-rock interaction tests also provide a way to characterize material properties of rocks, including uniaxial compressive strength and internal friction angle from scratch tests (Rostamsowlat et al., 2022; Zhang et al., 2022), elastic modulus and hardness from nanoindentation in shales (Liu et al., 2016), and hydraulic diffusivity from indentation in poroelastic and poroelastoplastic rocks (Liu and Huang, 2021).
Probabilistic Stope Stability Analysis Based on the Modified Stability Graph
Authors: de Préval C. Séguineau , Ouellet A. , Andrieux P. 
Published: August 2024

ABSTRACT:
The Stability Graph method is widely used to assess the stability of a stope. However, its traditional deterministic application overlooks the variability of the underlying rock mass parameters. By defining distribution functions for the rock mass parameters and running a Monte Carlo analysis on these inputs, the inherent rock mass variability is reflected in the outcome in the form of a distribution of the modified stability number N'. This paper presents guidelines on defining the input distribution functions, and particularly on elaborating the correlation between these distributions. Finally, methods are presented to interpret the obtained modified stability number distribution. The first method introduces a risk tolerance factor allowing to completely determine a stable stope. The second method identifies the drivers for instability, which could be used as variables for subsequent stope optimization.

1. STABILITY GRAPH METHOD
The sizing of open stopes for underground mines is of particular importance during the mine design. Several tools are available to support the engineers throughout the process. One of the most widely used methodology in Canada is the empirical Stability Graph Method, initially developed by Mathews et al. (1981). This method was modified by Potvin (1988) to better account for the specificities of Canadian hard rock mines.

1.1. Modified Stability Graph Method
The Stability Graph Method involves the calculation of two parameters: the modified stability number N′ and the hydraulic radius HR.
The modified stability number is defined as follows:
(equation)
where Q′ is the Q-system rock mass quality as defined by Barton (1974) with the stress reduction and water factors set to 1.0, and A, B and C the rock stress, joint orientation adjustment and surface orientation factors, respectively.
The modified Q′ value is defined by the following equation:
(equation)
with RQD the rock quality designation index, Jn the joint set number, Jr the joint roughness number and Ja the joint alteration number (Barton, 1974).
The three parameters A, B and C are evaluated graphically as shown in figures 1, 2 and 3, respectively.