bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fracture Geometries and Breakdown Pressures of Multi-Branch Radial Borehole Fracturing Influenced by Horizontal Stress Difference
Authors: Yong Yuning , Guo Zhaoquan , Tian Shouceng , Wang Tianyu , Sheng Mao , Liao Lulu 
Published: September 2023

ABSTRACT
Multi-branch radial boreholes can be drilled and combined with hydraulic fracturing to efficiently stimulate tight gas reservoirs. This paper experimentally investigates how horizontal stress difference affects fracture geometry and breakdown pressure in multi-branch radial borehole fracturing by a true triaxial fracturing device. Six artificial rocks (395 mm × 395 mm × 395 mm) were cast for the experiments, which are divided into two groups by the azimuth of the radial borehole. The results show that fracture geometries are controlled by the rectification of a single radial borehole, the extrusion between the adjacent radial borehole row, and the deflection of the maximum horizontal stress. Fracture propagation is affected by the dynamic variation of the three effects. Decreasing the stress difference is favorable for fracture propagation along the radial borehole axis, while it lifts the breakdown pressure. Decreasing the azimuth lifts fracture extension distance parallel to the radial borehole axis and reduces the breakdown pressure. This research sheds light on the feasibility of radial borehole fracturing for reservoirs under various stress differences.

INTRODUCTION
Horizontal wells combining multi-stage hydraulic fracturing technology are commonly used to extract tight gas reservoirs. However, it still has the challenge that is the insufficient stimulation. Radial borehole fracturing is proposed recently, which combines the horizontal radial borehole with hydraulic fracturing (Huang et al., 2020a; Huang et al., 2020b; Kamel, 2016; Landers, 1998). This technology has the following procedure. Firstly, several radial boreholes, with diameters of no more than 50 mm, are drilled perpendicular to the axis of the vertical well. The fracturing fluid is then injected into the radial boreholes via the main well. After fracturing, the complex fracture network is generated in the reservoir finally. It has been applied in many fields with good effect (Bruni et al., 2007; Cinelli and Kamel, 2013; Cirigliano and Blacutt, 2007; Li et al., 2000; Maut et al., 2017; Ragab and Kamel, 2013). The multi-branch radial boreholes are favorable to communicating several sweet spots in the tight gas reservoir, which is also more economical than horizontal wells. So, radial borehole fracturing is anticipated to efficiently develop tight gas reservoirs or other unconventional reservoirs.
Elasto-Plastic Damage and Dilation Analysis of Fibre-Reinforced Thin Spray-On Liner Coated Concrete and Coal Specimens Under Compressive Loading
Authors: Dondapati Gopi Krishna , Deb Debasis , Porter Ian , Karekal Shivakumar 
Published: September 2023

ABSTRACT
Skin support provides resistance to the shearing and spalling of exposed rock layers/blocks, as well as protecting the surface from open atmospheric contact. Thin spray-on liner (TSL) is one such skin support that can be applied to the roof or sidewalls of an excavation to enhance load-deformability behaviour. The failure behaviour of concrete and coal blocks when coated with a thin layer of polymeric liner was studied experimentally and numerically. The experimental results show a distinct "slight strain-softening zone" in the stress-strain curves of cubical concrete and coal samples when coated with a 5 mm thick polymeric liner. A micro-plane based coupled-damage-plasticity material model with the Drucker-Prager yield criterion is also implemented for determining the damage and dilation behaviour in the concrete and coal samples with and without liner. The results show that liner application reduces the magnitude of damage by nearly 23% in both concrete and coal blocks. On the other hand, the dilation angle increases rapidly to its peak value with an increase in plastic shear strain (γp).

INTRODUCTION
The design of structures in underground rock mass poses a unique problem to engineers from two fronts: i) before excavation, the rock is subjected to in-situ stresses, and ii) after excavation, protecting the skin of the exposed rock mass. Once the excavation is complete, the final stress state is a combination of in-situ and induced stresses (Brady & Brown, 2004). Loss of ground confinement results in softening of the skin of the excavation. It allows excessive displacements in radial and tangential directions, and causes considerable dilation. The situation worsens if the rock mass contains pre-existing geological discontinuities, material diversity, and water saturation. Lack of skin support may be one of the main factors for the key-block instability problem at the initial excavation stages. According to the key-block theory, if all potentially unstable wedges are supported, the remainder of the rock mass will remain stable due to its inability to move (Goodman, 1995). Potvin et al. (2001) suggest that liners can improve the control of small pieces of freshly exposed rocks near an active face. Skin support prevents the shearing and spalling of exposed rock layers/blocks and protects the surface from open atmospheric contact. According to Tannant (2001), small rock displacements at interactions between rock blocks are sufficient for the liner to start functioning.
Developing a Velocity Model for an Underground Coal Mine Using a Compressed Load Column Seismic Source
Authors: Boltz S. , Chambers D. , Sbai S. , Janson P. 
Published: September 2023

ABSTRACT
Induced seismicity is common in underground mining, particularly in mines that cave by design, such as longwall coal mining. Seismic monitoring is one of the few remote sensing technologies that provide an understanding of a mine's response to extraction. However, its effectiveness usually depends on understanding event locations in relation to the mine workings. A significant source of uncertainty in event locations is the velocity model: a description of the speed at which seismic energy propagates. A nondestructive, repeatable compressed load column seismic source (CLCSS) was developed for velocity model calibration in underground coal mines. This paper describes the CLCSS and its application at a longwall coal mine. Signals from the CLCSS were detected up to 950 m epicentrally (1,100 m hypocentrally) from the source. Using the ground-truthed signals from the seismic source, we estimate a velocity model for locating events from a surface geophone array. Model performance is evaluated by relocating mining-induced events with well-constrained locations. A three-layer model with P-wave velocities ranging from 3.6 km/s to 4.4 km/s and a VP/VS ratio of 2.1 performed best with location errors of approximately 100 m, which is sufficient for many applications of seismic monitoring in coal mines.

INTRODUCTION
Coal bursts—violent dynamic failures which cause damage to mine openings—were first documented in European coal mines well before World War I (Guan et al., 2009) and continue to threaten underground coal miners around the world. For example, approximately 280 significant bursts occurred in U.S. coal mines between 1983 and 2017, seven of which resulted in fatalities (Mark, 2018). In China, over 200 coal mines have reported bursts cumulatively resulting in over 1,000 injuries and 100 fatalities in the past 10 years (Rong et al., 2022). Poland's Upper Silesian Coal Basin has experienced over 100 significant events, some of which resulted in injuries and fatalities (Mutke et al., 2015). Several other countries have also reported coal mine bursts, including Japan, Australia, India, France, South Africa, Czechoslovakia, Canada, Germany, and Russia (Lama and Bodziony, 1998). Although bursting mechanisms are not well understood and vary considerably, studies have identified risk factors including depth of cover or rapid changes in topographic relief, thick brittle strata near the coal seam, inadequately designed pillars, multi-seam interactions, and a variety of other mining and geological factors (Mark and Guana, 2016).
Drilling Stuck Probability Intelligent Prediction Based on LSTM Considering Local Interpretability
Authors: Wang Jianhua , Guan Zhen , Liu Muchen , Song Xianzhi , Wang Zheng 
Published: September 2023

ABSTRACT
Stuck pipe in the drilling can increase the non-productive time and lead to drilling risks such as buried tool and drilling tool fracture. Due to complex sequential feature analysis and the lag of downhole data transmission, traditional methods which are mostly used for post-drilling analyses have poor timeliness and low accuracy so that it cannot meet the requirements of field application. This study provides a data-driven prediction method for stuck pipe probability. First, the dataset is established combining drilling records and logging data from 108 wells, and 15 input features are selected. Then, the intelligent prediction model based on the Long Short Term Memory (LSTM) network is developed considering the timing characteristics of drilling parameters. Finally, Shapley Additive Explanations (SHAP) is used to calculate the quantitative contribution of input parameters to solve the problem of the black box. The results show that the accuracy of the LSTM model is 97%. Through local interpretation and analysis, the model accords with the natural physical law. The proposed model has great timeliness, high accuracy, high reliability and quantitative risk prediction. This study provides useful insights into predicting stuck pipe risk.

INTRODUCTION
Drilling is the only way to get oil and gas which is an uncertain undertaking. Due to poor underground conditions, complex conditions (lost circulation, well collapse, stuck pipe, etc.) often occur, among which complicated conditions of stuck pipe often occur in the drilling construction process. According to Chunbo Zhao (1998), stuck drilling accidents account for 40%∼50% of the total drilling complications in western oilfields, which seriously restricts safe, economical, and efficient drilling. Therefore, the timely prediction of stuck pipe events is considered a primary necessity to assist the drilling team in the decision-making process, so that appropriate countermeasures can be put into effect before the situation slips out of hand.
Mudlog data shows that stuck pipe accidents occur in the process of tripping and drilling with varying degrees of severity. For example, in some highly deviated wells and horizontal wells, the stuck pipe accident is often accompanied by the process of tripping, but it is usually not serious. On the contrary, more attention is paid to the stuck pipe during drilling. Once the drill string is completely stuck, it can only be lifted by the explosion and a new side drilling scheme need to be redesigned, which seriously restricts the safety and efficiency of drilling. Therefore, we focus on the real-time prediction of stuck pipe in the process of drilling.
Estimating Subsurface Horizontal Stress Magnitudes in a Three-Dimensional Geocellular Model: Application to Permian Basin Unconventional Resources
Authors: Johns M. K. , Crawford B. R. , Amalokwu K. I. , Finn C. F. 
Published: September 2023

ABSTRACT
In situ stress prediction is critical for applications associated with unconventional resource development including drilling, hydraulic fracturing, enhanced oil recovery and induced seismicity. A range of model-driven approaches have been developed to predict variation of subsurface stresses with rock type and depth. For example, if we assume poroelastic coupling and anisotropic symmetry, quantifying the horizontal stress magnitudes with depth requires log-derived density, acoustic velocities, mineral composition, and pore-pressure properties as input, plus additional "tectonic strain" calibration to subsurface measurements. Estimating stresses in a 3D mechanical earth model (MEM) can be difficult away from well control. We present a novel workflow for simplifying theoretical stress calculations, then calibrating a seismic-driven MEM to log-based SHMIN profile(s). The workflow employs these calibration constants to propagate stress magnitudes throughout the 3D MEM based on 3D properties, which include SOVB and PRES, as well as seismic-inversion derived elastic properties and rock facies. Finally, the 3D MEM yields SHMIN profiles, maps, and cross-sections that are used for assessing stress across a development region, with examples shown from the Permian Basin of the USA.

INTRODUCTION
Knowledge of the in-situ state of stress is fundamental to all subsurface geomechanics/rock engineering endeavors. The prediction of layer-to-layer variation of horizontal principal stress magnitudes is vital for a wide range of energy-related applications including the following: drilling (wellbore stability); completions (hydraulic fracturing); mechanical seal capacity/caprock integrity (underground gas storage, carbon capture, utilization, and storage), in-fill drilling and field development (parent-child well interactions, depletion planning) and abandonment (annular barriers).
The magnitude and orientations of principal stresses can be directly measured. The magnitude of the minimum principal horizontal stress "SHMIN" is measured in the subsurface through identification of the closure pressure after shut-in of a "DFIT" diagnostic fracture injection test, which involves the pumping of a relatively small volume of water into a short wellbore interval over a brief period, also referred to as a minifrac test. The magnitude of the maximum principal horizontal stress "SHMAX" can be inferred from image log analysis of compressional (breakouts) and tensile (drilling induced tensile fractures) failures of the borehole wall (Zoback et al., 2003). Yet neither of these measurements is conducted at sufficiently high frequency or fine scale to enable adequate characterization of horizontal stress magnitude variation with depth, nor with lateral frequency, as required for practical engineering applications across a region.
Numerical Analysis on Characteristics of Cracks and ROP Enhancement Performance in Hard Rocks Subjected to Axial-Torsional Coupled Percussion
Authors: Sun Zhaowei , Wu Xiaoguang , Yang Rui , Huang Zhongwei , Shi Huaizhong , Mu Zongjie , Yu Huiyong 
Published: September 2023

ABSTRACT
Axial-torsional coupled percussive drilling (ATCPD) is a practical technique for creating volumetric breaking patterns and increasing rate of penetration (ROP) of hard rocks. Our paper focus on numerical investigations on ATCPD process. We employed a continuous-discrete coupling method based on cohesive elements to characterize the rock failure subjected to different percussion (axial, torsional and coupled percussion). Based on this model, the penetration-cutting process of the single cutter at different percussion modes was simulated, respectively. The corresponding cracks characteristics, penetration/cutting force and torque were analyzed. Rock scratch experiments were further conducted on granites to validate the model. The results show that the complex cracks propagation zone and the larger tensile cracks around the cutter are developed subjected to coupled percussion, resulting in larger failure elements number and cracks volume. That is, more significant macro damage is thought to form in coupled percussion, thereby increasing the penetration and cutting force of single cutter. It is worth noting that the coupled percussion mode can also generate stable fluctuation torque, which improves the ROP enhancement performance. Our results are expected to provide some guidance for efficient drilling in hard rocks.

INTRODUCTION
Increasing oil, gas, and heat reserves in deep formations will be critical in addressing the worldwide energy supply (Santos et al., 2000; Moore and Simmons, 2013; Hu et al., 2013). The construction of wells to exploit deeper energy in more challenging environments requires large investments, which are mainly related to the involved drilling operations (Abdo and Haneef, 2013; Diaz et al., 2017). For example, the reliance on drilling costs is especially high in the development of enhanced geothermal system (EGS), primarily because this method of obtaining geothermal energy necessitates the challenge of drilling deep holes in hard crystalline basement rocks, such as granites (Song et al., 2018; Anderson and Rezaie, 2019). These limiting factors pose a major challenge to our traditional drilling technologies (e.g. rotary drilling), whose poor performance in hard rocks, in terms of wearing of the drill bits and low penetration rates (Diaz et al., 2017; Rossi et al., 2020). As a result, the development of drilling techniques to increase the ROP enhancement effect in deep reservoir hard rocks has attracted more and more interest in the engineering field.
Size Effects on Crystalline Rocks Under Uniaxial Compression and Brazilian Tests
Authors: Sun Y. , Kwok C. Y. , Duan K. 
Published: September 2023

ABSTRACT
The tensile strength of crystalline rocks in Brazilian tests (BT) shows a more significant size dependency than the uniaxial compression strength in uniaxial compression tests (UCT), while the micro-mechanism is still unclear. This study seeks to elucidate the micro-mechanism by comparing different microcracking processes under UCT and BT. We adopt a grain-based model in the discrete element method (DEM) to reproduce the interlocked microstructure of crystalline rocks and perform UCT and BT with different sizes ranging from 0.5 to 3 times the standard sample size. It was found that peak stresses in UCT are nearly insensitive to sizes, which is consistent with experimental results measured at very low loading rates. Due to the homogenous stress distribution, no clear cracking paths are observed; instead, randomly distributed microcracks appear at failure. In contrast, numerical results indicate that the tensile strength measured in BT decreases as size increases and continuous cracking paths are observed at failure. Larger specimens have a higher possibility to include weaker cracking paths, hence tensile strength shows stronger size dependency. The findings of this work offer microscopic explanations for different size effects observed in UCT and BT, which can bridge the gap between laboratory-scale strength data and field-scale applications.

INTRODUCTION
Rock engineering applications often require assessing the strength and failure characteristics of rock masses. These rock masses are composed of intact blocks across various scales. However, the strength and cracking mechanism of these field-scale intact blocks are usually indirectly measured and studied through laboratory-scale tests on intact specimens (Duan et al., 2017; Duan and Kwok, 2015; Fei et al., 2021; Mahabadi et al., 2014; Martin and Chandler, 1994; Wong et al., 1996).
Uniaxial compression test (UCT) and Brazilian tests (BT) are standard tests that measure the uniaxial compression strength (σf) and tensile strength (σt) of rocks (Eberhardt et al., 1999; Li and Wong, 2013; Martin, 1994). The sizes of UCT and BT specimens in the laboratory usually vary from 5-10 cm in diameter, much smaller than in fields. However, a dependence of strength on size is widely known in rocks (Bažant, 1984; Choo et al., 2023; Paterson & Wong, 2005). The strength determined by these laboratory-scale tests may overestimate the loading capacity in fields, and the cracking process observed in the laboratory-scale specimens may also not accurately manifest the failure mechanism in the field scale. Therefore, to apply laboratory-scale experimental data to practical applications, it is vital to investigate the influence of specimen size on strength and cracking patterns.
Prediction of In-Situ Stresses by Using Machine Learning and Intelligent Optimization Algorithms
Authors: Zhang Haoze , Wu Bisheng , Nie Yuanxun , Zhang Xi , Chen Zhaowei 
Published: September 2023

ABSTRACT
In-situ stresses play an important role in affecting many geological processes such as hydraulic fracturing and CO2 storage, and a good understanding of the magnitude and direction of in-situ stresses is very important for deep energy exploitation. In this study, a machine learning model consisting of generative adversarial networks (GAN), particle swarm optimization (PSO) and support vector regression machine (SVRM) is proposed to predict the minimum in-situ horizontal principal stress (Shmin) from a series of existing experimental breakout data. First, the GAN and PSO are used to improve the quantity and quality of training data and to optimize the hyperparameters of the SVRM. Second, the enhanced training data are used to train the SVRM that predicts the Shmin based on the wellbore breakout geometries. In order to examine the reliability of this technique, the Shmin predicted from the proposed model is compared against the experimental data and it is found that the proposed model has a high accuracy with an average relative error of less than 10%. In addition, the proposed model requires only a few seconds to run on a laptop computer, thus providing a useful tool for accurate and efficient prediction of the Shmin.

INTRODUCTION
In-situ stresses play an important role in affecting many geological processes such as hydraulic fracturing and CO2 storage, and a good understanding of the magnitude and direction of in-situ stresses is very important for deep energy exploitation. During exploiting unconventional petroleum resources, drilling of a well and its stability depend on accurate measurement of in-situ stresses. Once the stress concentration at the borehole wall exceeds the rock strength, borehole failure occurs. In addition, in-situ stresses are closely related to earthquake faulting, volcanic eruptions and other geotechnical or geological processes. As a result, accurate measurement of in-situ stresses is of great significance.
Fracture Roughness Characterization from 360 Unrolled Core Images in a Sandstone Reservoir, Case Study, Algeria, Hassi Messaoud
Authors: Ifrene Ghoulem E. H. , Irofti Doina , Khouissat Abdelhakim , Pothana Prasad , Aihar Aimene , Li Bo 
Published: September 2023

ABSTRACT
Various existing indirect measurement methods and techniques in the petroleum industry are used to estimate some of the fracture parameters, such as sonic and electrical image logs. However, none of them can estimate the fracture roughness and the degree of mismatch between the two opposite fracture sides due to the sampling resolution. These two are important parameters to consider when dealing with geomechanics and fluid flow in tight naturally fractured reservoirs because they are important in quantifying shear strength and permeability. A quantification and detailed characterization of the joint roughness coefficient (JRC) and the degree of mismatch has been done on fractures gathered in a total of 23 wells in the Algerian Cambro -Ordovician oil-bearing formation Hassi Messaoud which consists of sandstone, clay, and some volcanic intrusions. These data have been collected from the digitalization of high-resolution unrolled 360-core photographs at the reservoir level. The results have been correlated with rock type, grain size, and fracture dip angle. Fracture roughness is ranging between 5 (low) to 19 (high) on the JRC scale and can be predicted from analysis of the general reservoir rock types (sandstone, eruptive, and clay). The results are applicable to other, especially siliciclastic reservoir lithologies, and will therefore contribute to defining a more accurate aperture and permeability estimation in building reliable Discrete Fracture Network (DFN) models.

INTRODUCTION
Fracture roughness is a key parameter in characterizing the permeability and fluid flow in petroleum (Camac et al., 2006) and geothermal systems (Porlles & Jabbari, 2022). As the majority of currently used large-scale models still significantly rely on simplified smooth parallel-plate models and its related models for naturally fractured reservoirs with rough walls, it is crucial to quantify the roughness in order to enhance the performance of these models (Bodin et al., 2007).