bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluation of Non-Destructive Stress Measurement Methods for Investigating Stress Memory in Rocks
Authors: Ali Z. , Karakus M. , Nguyen G. D. , Amrouch K. 
Published: September 2023

ABSTRACT
Rock bursts and spalling are major concerns for the design of deep underground structures under high in-situ stress conditions. A full constrain of in-situ stress magnitude and spatial distribution is therefore essential for managing the occurrence and severity of such phenomena. In recent decades, non-destructive stress measurement methods have been developed as a reliable alternative to traditional methods. These methods are based on rock stress memory and rely on accurate measurements of strain and acoustic data during uniaxial cyclic loading of specimens. In this study, several non-destructive stress measurement methods based on strain measurement and acoustic emission were evaluated. Uniaxial cyclic loading and unloading tests were performed on cylindrical specimens of Hawkesbury sandstone, and the deformation was monitored using strain gauges, Linear Variable Differential Transformer (LVDTs), Digital Image Correlation (DIC) and high-speed acoustic emission (AE) system. The strength and capability of each method in determining the applied stresses were evaluated by analyzing the strain and acoustic data collected during uniaxial cyclic loading. Although all methods were found effective in determining the applied stresses, our results indicate that the DRA and SMM methods were more precise and consistent.

INTRODUCTION
The Kaiser effect is a phenomenon observed in rock specimens when a uniaxial cyclic loading is applied in a laboratory. Acoustic emission (AE) activity begins just after the applied stress exceeds the peak of previously applied maximum stress to the specimen (Lavrov, 2002). This memory of previously applied stresses is found not only as a change in AE activity but also in the strain rate of rock specimens under a constant loading rate, known as the stress memory (Yamamoto et al., 2009). Kuwahara et al. (1990) proposed a model for the inelastic deformation of rock specimens under axial loading of compression to explain the mechanism of the Kaiser effect. According to Kuwahara et al. (1990) there are many potential micro-cracks in a rock specimen, and the strength of the specimen depends on potential cracks and applied stress to the specimen. If the applied stress is increased to a certain magnitude, all the potential micro-cracks with strengths smaller than the applied stress should initiate or propagate (Hoek and Martin, 2014). When the specimen is subjected to stress again after unloading, new micro-fractures hardly occur at first, and the pre-existing crack produced in the previous loading steadily moves with an increase in applied stress until the applied stress reaches the peak of the previously applied stress. New micro-fractures begin to occur only after the applied stress has reached the previous stress.
Unconfined Compressive Strength Estimation in the Shale Gas Reservoir Using Data Driven Technique
Authors: Shi Xian , Yang Yuanyuan , Liao Yong , Wang Daobing , Han Songcai , Gao Qi 
Published: September 2023

ABSTRACT
Identifying and predicting rock unconfined compressive strength is critical to well design, wellbore stability, and hydraulic fracturing stimulation in shales. However, accurate prediction of rock mechanical properties is hard in the absence of high-resolution advanced geophysical logs (e.g., image logs) and laboratory mechanical core samples. This study focuses on rock mechanical parameter estimation using three data-driven techniques: backpropagation (BP) network, support vector machine (SVM), and extreme learning machine (ELM) models in a shale gas reservoir. Additionally, this study aimed to obtain accurate rock mechanical properties, which have proven challenging using conventional petrophysical methods in wells without downhole core data. A total of 350 samples from 22 wells with laboratory measurement data were used to train and validate the neural network. Robust algorithms were used to provide fast and accurate prediction results, which were verified by comparing them with other approaches. The trained machine-learning models were cross-validated to check their robustness. The network model was then applied to estimate rock unconfined compressive strength for the remaining wells. The predicted results had a good match well with the laboratory test conclusions. Based on the estimations, rock mechanical properties were mapped and analyzed in the target shale gas zone. This method is helpful for geomechanical modeling in shale gas reservoirs.

INTRODUCTION
Uniaxial compressive strength is the ultimate ability of a rock specimen to resist damage under uniaxial pressure. When a rock is subjected to external forces, damage occurs when the stress reaches a certain limit value, which is the strength of the rock. As one of the most important mechanical indexes of rock, understanding the uniaxial compressive strength is necessary for hydraulic fracturing design and wellbore stability.
I To have a more accurate characterization of the reservoir geomechanical properties and the corresponding engineering parameters and to provide a basis for the later development of well pattern and stimulation scheme, well logging is generally used for the geomechanical properties prediction. However, due to the absence of several well logs and empirical parameters in the geomechanical modeling, accurate geomechanical properties estimation should be calibrated with laboratory experiments. However, in the absence of high-quality laboratory cores, it is challenging to accurately conduct experiments. Therefore, this study uses artificial intelligence techniques to predict uniaxial compressive strength by combining well logs and laboratory mechanical results.
Experimental Investigation of Fracture Initiation and Propagation Characteristics in Deep Coal Seams
Authors: Jian Wu , Libo Zhou , Qi An , Jianchuan Li , Fan Yang , Qi Yang , Yesong Li , Yao Jiang , Ben Li , Hui Li 
Published: September 2023

ABSTRACT
Deep coal seams usually require hydraulic fracturing to enhance the coalbed methane productivity due to their low permeability and low porosity features. Identifying the initiation and propagation mechanics of deep coal seams could help to optimize the hydraulic fracturing design and operations and effectively stimulate the fracture network system in coalbed methane. This paper designed and conducted lab-scale hydraulic fracturing experiments to evaluate the effects of frac-fluid viscosity, water pump rate, and coal bed lithologies on fracture initiation and propagation. Totally 10 outcrop coal samples were collected and cut to 10cm × 10cm × 10cm for fracturing physical simulation. The in-situ stress (stress-difference) of the LinXing(LX) coalbed (2000m vertical depth, Shanxi China) was used as confining stress of the experimental samples. Stimulated fracture surface area calculated from computerized tomography (CT) scan and three-dimensional reconstruction was used as the primary indicator to analyze the significance of hydraulic fracturing operation parameters. Results showed that water pump rate, frac-fluid viscosity, and perforation angle were the three significant factors that could affect the complexity of the fracture network (fracture propagation). As the water pump rate increased from 3ml/min to 7ml/min, both fracturing pressure and loading time increased. The pump rate contributes to the complex fracture network. As the viscosity of the frac-fluid increased from 10mPa·s to 50mPa·s, the fracturing pressure increased, and the complexity of fractures reduced. Among mudstone, coal, and mud-coal samples, the fracturing pressure of mudstone is highest, than is mud-coal rock, while the fracturing pressure of the coal sample is lowest. Fracturing pressure increased with the perforation angle increase (90°&gt;60°&gt;30°&gt;0°). The experimental results can provide fundamental data for the on-site deep coal seam fracturing design and optimization.

INTRODUCTION
Coalbed methane has been paid more and more attention in recent years (Cao et al., 2015; Li et al., 2017; Li et al., 2023). It is understood that the geological reserves of deep coalbed methane resources in China are about 22.45 trillion cubic meters, accounting for 61% of the total resources (Guo et al., 2015; Wang et al., 2022). As the unconventional oil and gas resource, the deep coal seam has poor physical properties, high stress, low permeability, and strong adsorption capacity, so the effect of conventional fracturing is not efficient (Qin and Shen, 2016; Yan et al., 2015; Chen et al., 2016; Li et al., 2018; Li, 2022).
Mechanical Characterization of Shale Minerals Based on Nanoindentation Technology
Authors: Li Lingdong , Liu Zhaoyang , Yu Wenhua , Lv Zehao , An Zhibo , Zhang Xiaoning , Duan Luyi 
Published: September 2023

ABSTRACT
Traditional macro-mechanical parameter testing methods, such as single-triaxial rock mechanics experiments, have high requirements on the size and integrity of rock samples. The nanoindentation technique has been gradually applied to the testing of rock mechanical properties, which provides an effective tool to measure rock mechanical properties at the nanoscale. In this paper, the shale samples from the Jimsar and Bohai Bay basins were used to obtain the microscopic mechanical parameters of the shale by nanoindentation experiments, and the Weibull model was used to evaluate the mechanical parameters of the two regions. The results show that both groups of samples have strong inhomogeneity and rich microscopic pore structure, with a larger elastic modulus of 35.23 GPa in the Jimsar Basin and a smaller elastic modulus of 26.78 GPa in the Bohai Bay Basin. In addition, the simulation results show that different mineral compositions have a strong influence on the nanoindentation curves, resulting in displacement-load curves deviating from the classical power exponential form and showing diverse anomalous features.

INTRODUCTION
Shale oil and gas, as an important unconventional energy source, greatly improves the world's energy supply structure (Du et al., 2018).The mechanical properties of shale reservoirs are crucial for the efficient extraction of shale oil and gas (Li et al., 2018). However, as a special kind of soft rock, shale is easily fractured and muddied, making coring operations very difficult (Ge et al., 2015; Yang et al., 2016). Coupled with the gradual development of mineral resource extraction to deeper depths and complex geological and tectonic environments, this poses a major challenge to traditional indoor tests to obtain shale rock mechanics parameters.
In recent years, nanoindentation experiments for the study of microscopic damage and measurement of micromechanical parameters at the nanoscale have been further developed. Oliver and Pharr (2011) invented indentation experimental techniques based on load and displacement measurements, where material hardness and modulus of elasticity can be determined directly from the indentation load-displacement curve, eliminating the need for other imaging techniques to assist. Indentation experiments have received a lot of attention from scholars due to their simplicity, efficiency and nondestructive nature. Nanoindentation has become a simple method to describe the mechanical properties of shale.
Study on the Elasto Viscoplastic Constitutive Model of Shale Influence on Fracture Conductivity
Authors: Li Shiyuan , Zhao Jingya 
Published: September 2023

ABSTRACT
Shale oil and gas reservoir is a new hotspot of oil and gas exploration and development. It is very important for fracturing production to produce artificial fractures with sufficient conductivity. Shale clay and organic matter content is high, which is easy to creep, and it makes the proppant embedded in the formation and affects the fracture conductivity.In this paper, an elasto-viscoplastic constitutive model is proposed to study the influence of shale creep on the conductivity. Isotropic linear elastic constitutive relation is adopted for elastic model, and the Perzyna model considering isotropic hardening is adopted for the viscoplastic model. Under the confining pressure of 5 MPa and the deviator stress of 10 MPa, 15 MPa and 20 MPa respectively, the triaxial compression creep experiments were carried out on the long 7 samples, and the material parameters in the viscoplastic model were determined by fitting the experimental data.The constitutive model is programmed into the user material subroutine UMAT of Abaqus using the return mapping algorithm. Then a triaxial compression numerical creep experimental model was established to verify the model. This model is applied to fracture conductivity model to study the influence of reservoir creep on the conductivity of artificial fractures and the sensitivity analysis of the influencing factors of fracture width was carried out.

INTRODUCTION
In the current context of "carbon peak" and "carbon neutral", the demand for natural gas as a clean and low-carbon fossil fuel is gradually increasing(Zhong et al., 2023). As an important source of natural gas, shale has attracted more and more attention(Katende et al., 2023). Hydraulic fracturing is the main means for developing of low-permeability oil fields such as shale (Maslowski & Labus, 2021). Whether to produce artificial fractures with sufficient conductivity is an important criterion for hydraulic fracturing evaluation(Lin et al., 2020).With the increase of closing pressure, the proppants at the fracture surface embed into the reservoir, and the embedded area is easy to block pores, rock crushing and shale flakes migrate, which hinders the flow of oil and gas(Zhang et al., 2014). In the porous media space composed of proppants, with the development of shale oil and gas, the proppant's effective stress increases, leading to the proppant being further embedded in the fracture surface.
Study of the Influence of Structural Parameters on the Output Characteristics of Torsional Impact Tools
Authors: Xin H. , Liu G. H. , Tian C. , Li J. 
Published: September 2023

ABSTRACT
Torsional impact tools can effectively eliminate the stick-slip vibration of the drill bit, which can effectively increase the mechanical drilling speed. In this paper, a mathematical model of the motion of a torque-influenced tool is developed based on an analysis of the structure and working principle of the tool. The influence of structural parameters on the output characteristics of the tool was analyzed by taking the shock frequency and impact work as the evaluation criteria for the output characteristics of the tool. The results show that the motion of the pendulum and reversing value are non-linear at different stages. The impact frequency and impact power of the tool decrease with the increase of the nozzle diameter, increasing first and then decreasing with the increase of the gap between the pendulum and the outer casing, increasing with the increase of the drain hole area on the wall of the baffle and pendulum, and remain stable after reaching the peak and no longer increase. To obtain better output performance, the pendulum clearance and drain area of the tool have optimal values in the design of structural parameters. The research results have important reference significance for the design of torque impact tools.

INTRODUCTION
The PDC bit is prone to stick-slip vibration when drilling in hard strata, which seriously affects the mechanical drilling speed and bit life. Torsional impact tools produce high frequency, low amplitude impacts and are often used on the top of the drill to reduce or eliminate stick-slip vibration. Various structures of torsional impact tools have been designed. The field application practice shows that in order to achieve good drilling speed, different areas have different requirements for the impact power and frequency of the tools (Zhou et al, 2012). Scholars have conducted some research on the analysis of the kinematic characteristics of torsional impact tools and the calculation of output characteristics. Tian Jialin established a kinematic calculation model of torsional impact tools and analyzed the influence of inlet pressure and flow rate changes on the tool impact frequency (Tian et al, 2016). Wang Wei and established a kinematic mathematical model of impact tools and analyzed the nozzle size and displacement on the tool output characteristics. The effect of nozzle size and displacement on the output characteristics of the tool was analyzed (Wang et al, 2019).
Stress Variation Around the Balarud Lineament in the Zagros Fold and Thrust Belt and its Implication for Reservoir Geomechanics
Authors: Yaghoubi A. , Dusseault M. B. , Leonenko Y. 
Published: September 2023

ABSTRACT
We investigate horizontal stress variation in the vicinity of the deep-seated Balarud Lineament in the northern part of Iran's Dezful Embayment in the Zagros Fold and Thrust Belt (ZFTB). Both petrophysical data from drilled oil and gas wells (3-4 km deep) and earthquake focal plane solutions (6 to 25 km deep) are used to constrain the orientation and relative magnitudes of the local and regional stresses. The stress orientations in the sedimentary rock strata and the basement are of two entirely distinct types. In the basement, constant regional NE-SW SHmax orientation is observed in the northern ZFTB. The seismologically determined local SHmax direction from 25 focal mechanisms around the Balarud Lineament is 29.3°±8.5°. However, observations of borehole breakouts and tensile-induced fractures indicate that the dominant SHmax orientation is N-S near the Balarud Lineament. The consistent stress direction in the basement indicates a high differential horizontal stress magnitude, whereas the principal stress orientation rotates 35° counter-clockwise in the sedimentary cover where the state of stress is extensional. The Lineament's second-order stress patterns are discussed in terms of wellbore placement and completion decisions.

INTRODUCTION
Anomalous relative stress magnitudes and orientations have been observed in the world's various uniform lithospheric stress fields. Stress deflection may be observed due to lateral density/strength contrasts, flexural stresses, or superimposed geological structures such as faults (Sonder, 1990) and salt diapirs (Dusseault et al., 2004). In the east-west-trending Transverse Ranges (California), the horizontal stress orientation is different by 25° from the reference stress state in the NW-SE San Andreas fault (Sonder, 1990). The regional NE-SW SHmax is reoriented to N-S in the area overlying the Peace River Arch in the Western Canadian Sedimentary Basin (Bell & McCallum, 1990). The same phenomenon is reported for the Amazon rift in central Brazil (Zoback & Richardson, 1996) and in the Swiss Alps and the northern Alpines foreland (Kastrup et al., 2004). Stress deflections can also be caused by reservoir depletion (Yale et al., 1994) and by earthquakes (Hauksson, 1994). Hauksson (1994) observed a 15° (±10°) rotation of local stress axes due to the 1992 Mw = 7.3 Landers's earthquake sequence. The scale at which second-order stress patterns occur depends on the degree of lateral density/strength contrasts and the size of geological structures and their orientation relative to regional stress fields (Sonder, 1990; Zoback, 1992).
Thermal Effect on Cement State of Stress in a Cement-Casing Structure
Authors: Meng M. , Frash L. P. , Carey J. W. 
Published: September 2023

ABSTRACT
Temperature fluctuations within a wellbore are common occurrences in various applications, including carbon sequestration, hydrogen storage, and thermal storage. To ensure long-term well integrity, it is necessary to investigate the mechanical response of the cement annulus under thermal loading. In this study, we designed a two-layer cement casing structure to evaluate the stress state at the cement-casing interface under high pressure and high temperature conditions. We cured Class-G cement with a water-cement ratio of 0.4 and poured it inside the casing, subjecting it to 40 MPa and room temperature for seven days before elevating the temperature to 35, 45, 55, and 65°C. After correcting for casing thermal expansion, we found that the cement-casing interface stresses were 9.2, 11.1, 16.4, and 22.7 MPa under these temperatures, respectively. The corresponding coefficient of thermal expansion of the cement was 1.6 × 10−5 /°C. Throughout the experiment, there was no water exchange between the curing cement and the external reservoir. The cement pore pressure dropped to nearly zero after seven days of hydration, but it increased significantly with the elevated temperature and dissipated slowly. Additional tests are needed to correct for the pore pressure effect on the cement-casing interface state stress. Overall, this work contributes to a better understanding of cement's pore-mechanical behavior with thermal cycling under subsurface conditions.

INTRODUCTION
The global energy sector is shifting from fossil based systems to clean energy resources in response to the growing concern about climate change. The topics of carbon sequestration, hydrogen storage, and thermal storage become the target of the whole society. Despite this shift, wellbore remain the primary effective channel connecting subsurface space utilization and ground activities, making long-term well integrity crucial to ensure sustainable, reliable, and efficient energy storage and sequestration.
In a typical wellbore, cement annulus is usually the most vulnerable part, therefore, we care about cement's overall performance in maintaining zonal isolation, including rheological properties, chemical properties, and mechanical properties [1]. Usually, researchers propose new formulations with specific types of additives to improve displacement efficiency, reduce chemical shrinkage, and promote proper mechanical strength. Of all the aspects of performance, cement mechanical behavior directly determine the quality of zonal isolation throughout its functional life.