bluuebunny/crossref_metadata_2025_split huggingface dataset:
Longwall-Induced Deformations and Shale Gas Well Casing Stresses: Engineering Principles
Authors: Su Daniel W. , Zhang Peter 
Published: September 2023

ABSTRACT
This paper summarizes important findings from the ongoing National Institute for Occupational Safety and Health (NIOSH) gas well stability research. Over the past seven years, field instrumentation results from NIOSH case studies and active mine-by case studies indicate that, under shallower covers, the measured horizontal displacements within the longwall abutment pillar are one order of magnitude higher than those measured under deep cover. Longwall-induced horizontal displacements occur along weak-to-strong rock interfaces; the sharper the bending stiffness contrast across the interfaces, the larger the longwall-induced horizontal displacements. Longwall-induced vertical compressions under shallower covers are, on the other hand, one order of magnitude lower than those under deep covers. Subsurface strata dip may magnify or reduce longwall-induced horizontal displacements. Uncemented production casings serve to uncouple longwall-induced deformations and stresses from the production casing. A case study is presented to illustrate the importance of leaving the production casing uncemented.

INTRODUCTION
Since 2003, over 1,800 unconventional shale gas wells have been drilled through active and future Pittsburgh Seam coal reserves in Pennsylvania, West Virginia, and Ohio. These unconventional gas wells, whether tapped into the Marcellus or Utica formations, contain very high gas pressure and volume. Strata deformations associated with underground longwall coal mining could induce stresses and deformations in the shale gas well casings, which in certain situations could compromise the mechanical integrity of the production, intermediate, and coal protection casings. Damaged well casings could potentially introduce high-pressure, high-volume explosive gas into underground mine workings to jeopardize underground miners’ safety and health.
To provide critical scientific data to the stakeholders, which includes the Mine Safety and Health Administration (MSHA), the Pennsylvania Department of Environmental Protection (PADEP), the West Virginia Department of Mine Safety (WVDMS), the Ohio Department of Natural Resources (OHDNR), coal operators, and gas operators, NIOSH initiated a research program in 2016 to evaluate the effects of longwall-induced deformations on shale gas well casing stability under deep as well as shallow covers. The effects of longwall-induced subsurface deformations on shale gas well casing stability under deep cover, under medium cover, and under shallow cover were published previously (Su et al., 2018a and 2018b; Su et al., 2019a and 2019b; Su et al., 2020; Zhang et al., 2020; Su and Zhang, 2021; Su et al., 2021). This paper focuses on a case study that illustrates the importance of leaving the production casing uncemented.
Impact of Drilling Mud Intrusion on Borehole Stability in Naturally Fractured Rocks: A Coupled DEM-DFN Investigation
Authors: Wei Yaoran , Feng Yongcun , Yang Tianyu , Tan Zhenlai , Dai Zhiyue , Li Xiaorong 
Published: September 2023

ABSTRACT
Borehole instability in naturally fractured rocks poses significant challenges to drilling. However, the weakening of fracture strength due to mud intrusion was not considered in most existing borehole stability analyses, which may yield significant errors and misleading predictions. In addition, the fracture distribution was oversimplified. In this paper, the impacts of mud intrusion on borehole stability in fractured rocks under anisotropic stress states are investigated using a coupled DEM (distinct element method) and DFN (discrete fracture network) method. A simplified, but reasonably realistic approach is developed to take into account the weakening of fracture strength due to mud intrusion. The results show that mud intrusion and associated weakening of fracture strength and hydro-mechanical coupling effect cause more shear failure of natural fractures and rocks, explaining why the increase in mud weight worsens borehole stability during overbalanced drilling in fractured rocks. This study provides a directly quantitative prediction method of borehole instability in naturally fractured formations based on the consideration of mud intrusion and its weakening of fracture strength.

INTRODUCTION
Borehole instability is a phenomenon that the borehole size and its structural integrity can not be maintained in the openhole interval. Maintaining a stable borehole is of great importance because related instability problems pose negative influences on the drilling schedule and costs, and even lead to the abandonment of the well (Chen et al., 2003; Zhang, 2013; Li et al., 2019). Various factors that affect borehole stability were investigated to explain the mechanism involved with wellbore collapse such as mud weight, in-situ stress, wellbore trajectory, rock properties, and failure criteria (Zhao et al., 2012; Mansourizadeh et al., 2016; Liu et al., 2021; Li et al., 2019; Zhang et al., 2020; Li et al., 2022; Aslannezhad et al., 2021). Both theoretical and field data have indicated that an appropriate increase in mud weight does benefit wellbore stability in continuous media (Salehi et al., 2010; Fan et al., 2020; Ibrahim, 2021; Motahari et al., 2022). However, compared with non-fracture formation, increasing mud weight may negatively impact wellbore stability in naturally fractured rocks (Santarelli et al., 1992; Yamamoto et al., 2002). It has been demonstrated that the role of drilling mud in maintaining borehole stability should be reconsidered when drilling in fractured rock formations. In addition, the mechanism of coupling effect of in-situ stress anisotropy, natural fractures, and drilling mud intrusion on borehole stability has not been fully understood.
The Effect of Rock Heterogeneity on Fracture Initiation During Supercritical CO2 Fracturing
Authors: Yang Bing , Yang Hong , Ren Lingying , Zhu Rongting , Huang Hai , Wang Haizhu , Ni Jun , Zheng Yong , Zhang Wentong 
Published: September 2023

ABSTRACT
To solve the issues during large-scale hydraulic fracturing such as massive consumption of water, formation damage and environmental contamination, etc., supercritical CO2 (SC-CO2) has been introduced as an alternative anhydrous-fracturing fluid. However, the heterogeneity of formation would have significant impact on fracture initiation. In this study, a series of tight sandstones was collected to perform SC-CO2 fracturing experiment. The effects of bedding-plane angle (BPA) and permeability of sandstone on fracture initiation are investigated. The results indicate that the initiation pressure of rock shows a fluctuating trend, it goes up firstly, then slightly goes down with the increasing of BPA. And the fracture morphology is significantly affected by the heterogeneity of rock, which are more inclined to distribute along the bedding planes. Moreover, the rocks with lower permeability have higher initiation pressure, and more complicated fractures would be induced. With the increasing of the permeability, the initiation pressure of rock reduce significantly, also the fractures morphology are gradually simplified. When the permeability reaches to 0.5 mD, the rock cannot be broken by SC-CO2 in the experimental pumping rate, but it can be fractured by water. It means that SC-CO2 as fracturing fluid is more appropriate to implement in low permeability reservoirs since its low viscosity and strong penetration. This research explores the formation adaptability and provides theoretical guidance for field application of SC-CO2 fracturing.

INTRODUCTION
Tight gas as typically unconventional reservoir, is widely distributed in China, which will play a significant role in the supplement of conventional hydrocarbon. According to the fourth oil and gas resource evaluation of CNPC, China's total onshore tight gas resources are 21.85 × 1012 m3, with 60% of the total resources in the Ordos Basin (Jia et al. 2022). Tight sandstone gas resource is usually with porosity less than 10%, in-situ permeability less than 0.1 mD, pore throat diameter less than 1 μm, and gas saturation less than 60% (Jia et al. 2012; Gong et al. 2016). These reservoirs cannot be produced directly without artificial stimulation method (Scanlon et al. 2014; Ma et al. 2015).
Three-Dimensional High Efficiency Fracturing Technology for Preventing Casing Deformation in W Deep Shale Gas
Authors: Wei Ran , Xiaobing Bian , Xudong Zhang , Bo Xiao , Nai Cao , Luo Zuo , Jinlong Du , Yuan Su 
Published: September 2023

ABSTRACT
The right of W mineral cover an area of 143.77km2. As shale gas horizontal wells are prone to casing deformation by segmental fracturing, the casing deformation rate exceeds 45%, which seriously affects the production capacity construction of shale gas wells in W block. A set of techniques for high-strength balanced fracturing process in multiple clusters for preventing casing deformation in W shale gas wells has been developed, including: 1) two evaluation indexes, namely stress-strain brittleness index and vertical stress and difference index between vertical stress and minimum horizontal stress, have been added to establish W deep shale fracturing quality evaluation index plate and realize fine division of segment clusters; 2) a multi-scale fracture network fracturing numerical model for W Shale gas wells was established for the first time via Eclipese software, and key fracture parameters such as optimal fracture half-length, flow conductivity and complexity were obtained; 3) in engineering construction, a multi-cluster, small particle size and variable displacement combination injection fracturing scheme has been proposed for two injection modes: planar perforation and spiral perforation, respectively, with the objective of reducing casing.

INTRODUCTION
Shale gas, as a new unconventional natural gas resource, occupies an increasingly important position in the energy sector. The economic development of deep shale gas in the US has gone through a process of continuous exploration and testing, improvement and refinement, with some blocks now meeting the requirements for economic development. Among them, 3 deep shale gas blocks in Haynesville, Eagle Ford and Canna Woodford with burial depths of 3500-4100m have been economically developed with single well gas production of more than 5×104m3/d after segmental fracturing of horizontal wells, with an average final gas recovery of more than 1×108m3 per well and an integrated cost of less than US$12 million per well (T.Lowe et al.,2014; Mauricio et al.,2013).
Hydraulic Fracturing of a Tight Conglomerate Sample with Distributed Optical Fibre Monitoring
Authors: Wang Zhenyu , Lin Botao 
Published: September 2023

ABSTRACT
In this paper, a distributed fiber-optic monitoring system is used to finely portray the effect of gravel on crack extension during a true triaxial physical simulation experiment. The experimental results show that under the control of stress difference, the obstruction effect of large-grained gravels on cracks is much higher than that of small-grained gravels on cracks. The fracture encounters the large-grained gravels to wind around the gravels mainly, and the fracture produces more microfractures within the rock. The waterfall cloud map shows a greater variation in the stretching and compression regions. When the fractures encounter small gravels, the fractures are still predominantly gravel-wrapping with some gravel penetration, and the strain distribution on the waterfall cloud diagram is uniform. When the gravel is disordered, the fracture morphology is complex and diverse.

INTRODUCTION
Conglomerate reservoirs are low porosity and low permeability. Hydraulic fracturing technology contributes to the efficient development of conglomerate reservoirs. The shape of the sewing mesh after pressing affects the final production result (Kang et al., 2020). Conglomerate reservoirs, another key development target in China after shale, have large development potential. Due to the high non-homogeneity of conglomerate, The extension of fractures in conglomerate reservoirs is affected by complex mechanisms, and characterization of fracture morphology is more difficult (Tang et al., 2022). Some scholars have conducted indoor experimental studies on the hydraulic fracture morphology of conglomerate reservoirs.
Ren et al. found that hydraulic fractures extend along the edges of conglomerate grains by large-scale physical simulations with conglomerate outcrops (Ren et al., 2023). Liu et al. used the baikouquan formation of the Mahu depression as the object of study. The indentation hardness tests found that the gravel was 5.3 times harder than matrix hardness (Liu et al., 2014). Li experimentally clarified several forms of fractures and gravels (Li et al., 2013).
Experimental Investigation of Mechanical Characteristics in Tight Sandstones by Combining Nanoindentation and AFM
Authors: Zhang Wentong , Wen Fugui , Tong Shaokai , Ren Lingying , Ni Jun , Huang Hai , Yang Bing , Ning Zhengfu , Jia Zejiang , Lyu Fangtao 
Published: September 2023

ABSTRACT
Acquiring the micromechanical property of phases in tight sandstones by conventional mechanical testing is a big challenge because of the heterogeneity and complexity of mineralogical composition in sandstone systems. In this study, nanoindentation and AFM (atomic force microscope) technologies were employed to figure out the mechanical characteristic of tight sandstones. Nanoindentation results show that the average Young modulus of quartz is 72.78 GPa in tight sandstones. We found that nanoindentation needs more methods like SEM and EDS to separate the modulus of phases in tight sandstone. In contrast, AFM can easily recognize the elastic modulus of various phases with high accuracy and distinction. AFM results show that the Young modulus of quartz is 7.4 GPa and the Young modulus of minerals is 2.28 GPa. Moreover, the modulus value in nanoindentation is higher than that in AFM. The difference in modulus results of quartz by AFM and nanoindentation is due to the selection in probe in AFM. Overall, it shows that AFM is more suitable for achieving the goal of identifying the modulus of various phases in tight sandstones. The knowledge obtained from this paper is promising in the application of nanoindentation and AFM in tight sandstones. It will also benefit the study of micromechanical characteristics of various phases in tight sandstones.

INTRODUCTION
Acquiring the mechanical property is beneficial for several engineering aspects. Such as designing hydraulic fracturing schemes, enhancing oil recovery, and keeping wellhole stability(Li et al., 2019; Shen et al., 2022; Q. Wang et al., 2022). Rock consisting of several minerals is widely accepted as a homogenous and complex material. In the conventional mechanical tests, the obtained results represent the overall mechanical characterization of rock, which is regarded as the identical mechanical property of minerals (Brotóns et al., 2013). Uniaxial and triaxial pressure tests are typically applied to characterize the mechanical property of rock(Palchik, 2011; J. Wang et al., 2021). However, from the micro-scale, there are different pore structures and components of the minerals in the rock. The result is that the micromechanical characterizations between several minerals differ a lot(Liu et al., 2021; Wu et al., 2020). Therefore, acquiring the micromechanical property of phases in rocks by conventional mechanical testing is a big challenge because of the heterogeneity and complexity of mineralogical composition in rock systems(T. Wang et al., 2022). That is to say, by obtaining the micro-mechanical properties of phases of minerals in the rock, we can have an explicit knowledge of the mechanical property of rock.
A Data Augmentation Method of Variable Density Logging Image Based on GAN
Authors: Wang Z. , Song X. Z. , Li Z. , Zhang Y. L. , Yang X. Y. , Pan T. , Zhu Z. P. 
Published: September 2023

ABSTRACT
In recent years, with the development of artificial intelligence technology, cementing quality evaluation models based on supervised learning algorithms have been gradually proposed and applied. These models automatically evaluate cementing quality by identifying variable density logging images. However, due to the uneven number of training samples (variable density logging images), the accuracy of automatic evaluation models is low, to solve this problem, this paper proposes a Wasserstein distance generation countermeasure network (VDL-WGAN) for variable density well logging images. In VDL-WGAN, the generator network uses reconstruction loss to improve the image generation ability of the model. To evaluate image quality, this paper calculates the PSNR and SSIM values of the generated images and trains the optimal model. After expanding the samples, the intelligent evaluation model of cementing quality is trained to improve the recognition accuracy. The VDL-WGAN proposed in this paper can improve the generation of high-quality virtual samples of logging variable density images, improve the accuracy of the intelligent evaluation model of cementing bond quality, and achieve the effect of data expansion.

INTRODUCTION
The quality of cementing is related to the output and life of oil and gas wells. If the quality of cementing is not good, it will not only bring difficulties to the subsequent drilling and testing, but also greatly affect the production life of oil wells (Ravi et al, 1996). Therefore, it is of great significance to accurately evaluate the quality of cementing. At this stage, the most common method is to use the variable density logging image for evaluation. The logging interpretation experts evaluate the cement bond quality by observing the light, dark and thickness of the strips in the variable density logging image. However, the manual interpretation method has gradually revealed its disadvantages, and the efficiency of manual evaluation of cementing quality is low (Fang et al, 2022). With the rapid development of depth learning, many researchers have proposed to use convolution neural network to recognize the image of VDL to improve the interpretation efficiency (Fang et al, 2022, Viggen et al, 2020, Voleti et al, 2020). However, these methods need a lot of data to support their training, and the number of logging variable density data images is limited.
Prediction of Ground Movements Under Dipping Seam Conditions
Authors: Romero Benitez J. D. , Maldonado E. , Agioutantis Z. 
Published: September 2023

ABSTRACT
The prediction of ground movements due to underground coal mining and their impacts on the surface are important considerations that have been studied by numerous researchers around the world. The majority of these studies have focused on the development of different analytical and empirical models for the prediction and calculation of ground deformation indices for either flat or gently dipping seams under variable topography. However, a few studies are available with respect to the prediction of ground movements under dipping seam conditions. Dipping seam conditions have been encountered in some cases in the US, where the inclination (dip) may be in the range of 10 degrees or greater. Ground movements under such conditions are evaluated using methodologies which assume horizontal seams for their calculations. In order to accurately predict subsidence under these conditions it is necessary to develop an appropriate methodology that builds on the existing infrastructure. This paper presents a methodology that can be used to model subsidence under dipping seam conditions. The methodology has been validated with two case studies that are available in the literature.

INTRODUCTION
Although new alternative energy sources are being developed, non-renewable carbon-based resources still constitute the base energy supply for many countries in the world. Coal production, 69% of which corresponds to electricity and heat generation (Çelik, & Özçelik, 2023), still plays an essential role in meeting the worldwide demand. The reduction of open-pit coal reserves has raised the need for underground coal mining, and, consequently, the need to enhance underground mining methods and technologies.
Although horizontal or near-horizontal coal seams constitute the majority of coal deposits currently extracted using underground mining methods, inclined seams are also being mined and will be mined even more in the future. Some countries, such as China, India, and Spain, classify high-quality reserves of coal as inclined strata (Afsari,1998).
Numerical Simulation and Operational Parameter Optimization for Staged Multi-Cluster Fracturing Horizontal Wells in Coal Seam Roof
Authors: Shi Hongwei , Zhao Haifeng , Li Xuejiao , Yao Wenji 
Published: September 2023

ABSTRACT
The staged multi-cluster hydraulic fracturing technique of horizontal well in roof strata of coal seam is a new method for effective developing the broken-soft coal seam. Therefore, based on cohesive model and Bernoulli equation, considering the friction of fracturing fluid flowing through wellbore, perforation and the stress interference during fracture propagation, a finite element numerical model of multi-cluster fracturing of coal seam roof coupling wellbore and formation is established. The effects of perforation diameter, perforation number and injection rate on fracture extension were studied. The results indicated the fracture tip is always located in the roof during fracture dynamic propagation, and coal seam fractures are wider than roof fractures. During multi-cluster perforation in the fracturing section, the fractures initiated from each perforation cluster have competitive propagation. The stress interference between the fractures and the friction of the fracturing fluid make the distribution of the fracturing fluid between the perforation clusters uneven. Increasing injection rate, reducing number of single perforation cluster, and decreasing diameter of perforations hole can facilitate the even propagation of fractures in each cluster, and increasing the stimulated reservoir volume. The influence of the perforation diameter is significantly greater than the injection rate and perforations number.

INTRODUCTION
China has a wide distribution of broken soft coal seams that have low permeability, and hydraulic fracturing is the key to its efficient development. However, due to their low strength(S), low elastic modulus(E), and high Poisson's Ratio(ν), broken-soft coal seams have high plasticity compared to hard coals or other rocks (Li et al., 2021; Lyu et al., 2020). Long fractures are difficult to form in coal seams and the fracturing sand is severely inlaid when conduct hydraulic fracturing in the plastic broken soft coal seam directly. The stimulation effect is generally poor. In response to this problem, scholars have proposed indirect fracturing technology for coal seam roof. (Li et al., 2014; Olsen et al., 2007; Olsen et al., 2003; Zhang et al., 2018). The technology realizes the efficient extraction of coalbed methane in broken soft coal seam by arranging horizontal wells in the roof strata adjacent to the coal seam, and the fracture extends from the coal seam roof to the coal seam. The field test indicates that the application of this approach to broken soft low-permeability coal seam can significantly improve the efficiency of coalbed methane exploitation (Zhang and Bian, 2015).