bluuebunny/crossref_metadata_2025_split huggingface dataset:
Laboratory Study of Fracture Propagation Behaviors in Fractured-Cavity Carbonate Reservoirs in Shunbei Oilfield
Authors: Luo Pandeng , Li Chunyue , Sun Yaoyao , Huang Zhongwei , Wu Xiaoguang , Zhang Xu , Yang Ruiyue , Wang Zikang 
Published: August 2024

ABSTRACT:
In order to determine the interaction behaviors between artificial fracture and nature fracture-cavity, we performed a laboratory true tri-axial fracturing experiment on natural carbonate outcrops with Mico-fracture and pores, and the natural fracture-cavity are simulated by pre-existing fracture-cavity. The propagation of artificial fractures is investigated by changing the approach angle for fracture and maximum horizontal stress, and arrangement of pre-existing cavity. Moreover, re-injection experiments are used to evaluate the conductivity of fractures. The results indicate that the extension of fractures in pre-existing fractured-cavity carbonate rocks is random. The extension of artificial fracture is steering when it encounters pre-existing cavity. Three interaction modes occur between artificial fracture and pre-existing fracture, and the large approach angle allows the artificial fracture to pass through the pre-existing fracture. Artificial fracture is always captured by pre-existing fracture, and the tortuosity is greater in the process of propagation. The breakdown pressure of pre-existing fracture-cavity carbonate rocks is about 50% lower compared to that of tight carbonate rock. Pre-existing fracture-cavity make the conductivity greater of effective fracture, but the length of effective fracture is not conducive to the conductivity. This research may contribute to the field application of hydraulic fracturing in carbonate formation.

1. INTRODUCTION
The increase of burial depth causes the gradual decrease of carbonate porosity, which is a past view on the lack of high-quality reservoirs in deep carbonate rocks (SCHMOKER J W et al., 1982; EHRENBERG S N et al., 2009). In recent years, 60 % of the world ‘s new oil and gas reserves come from deep strata, and the exploration potential is huge (Wei C et al., 2017; Sun K et al., 2022). The deep strata of oil and gas reserves and production of marine carbonate rocks in Tarim Basin, Sichuan Basin and Ordos Basin have been increasing rapidly year by year, which has attracted wide attention from the industry. In the proven deep strata of carbonate reservoirs, two-thirds belonging to the type of fractured-cavity reservoirs (Guo W et al., 2022). Complex spatial structure is the characteristic of fractured-cavity reservoir, mainly including matrix pores, karst cavity, and natural fractures with different development degrees (Durrani M Z A et al., 2021; Tian F et al.,2019; Sun, K et al., 2021). Due to the extreme heterogeneity and complex flow environment of facture-cavity carbonate formation, that is a challenge to increase oil and gas extraction rate (Tian F et al.,2016; Dmitriy A. Martyushev et al., 2022).
Evaluating Geological Seals for Underground Hydrogen Storage: A Comprehensive Assessment
Authors: Galvis-Silva Henry , Okoroafor Esuru R. , Liu Kai-Wei 
Published: August 2024

ABSTRACT:
Underground Hydrogen Storage in porous media offers a viable solution for long-term, large-scale energy storage. Yet, challenges such as low storage efficiencies and potential losses persist, with a key issue being the sealing capacity and integrity of the storage reservoir. This study specifically addresses two primary hydrogen leakage mechanisms in caprocks: capillary leakage and faults or fractures in the caprock. We conducted static reactivity tests on various shale samples, at a constant pressure of 3.4 MPa and exposed to hydrogen in the presence of brine under different temperature conditions over 30-day periods.
The findings generally indicate low reactivity of hydrogen with the shale samples. Minor compositional changes were observed, which were determined through XRD analysis. However, significant alterations in petrophysical properties were observed in all the plug samples, including more than a 100% increment in porosity and even greater changes in permeability. Additionally, uniaxial compressive strength tests were conducted, revealing that the shales exhibited a reduction in all mechanical properties. Micro-CT scans confirmed the increases in permeability and exposed the presence of small microcracks.
These findings underscore the potential for hydrogen storage to modify shale structure by reopening microcracks, emphasizing the need for further research to fully understand the geochemical interactions at play.

1. INTRODUCTION
The urgency of transitioning to a clean, low-carbon energy future underscores the pivotal role of energy storage technologies. These technologies are crucial for integrating intermittent renewable energy sources, such as wind and solar, into the electrical grid to ensure a consistent energy supply. Particularly, large-scale energy storage is instrumental in facilitating the shift towards more sustainable energy systems, a topic that has gained prominence in recent research (Krevor et al., 2023).
A primary challenge in the renewable energy sector is the mismatch between the periods of energy production and peak demand times (Matos et al., 2019), as depicted in Figure 1. This discrepancy underscores the critical need for efficient energy storage solutions that can store excess energy during high production periods and release it during peak demand times. The transition towards renewable energy sources amplifies the urgency for such solutions to combat climate change.
Use of Combined Analytical and Numerical Sand Production Prediction Methods to Define Simple Cut-Off for Sand Control and Well Completion Selection
Authors: Khaksar A. , Younessi A. R. , Likrama F. , Gui F. 
Published: August 2024

ABSTRACT:
There are several sanding prediction techniques commonly used by well engineers and geomechanics specialists. The most desirable ones are empirical models with simple rules but these need a vast amount of field observations and historical production data to derive the appropriate cut-offs. We introduce a geomechanical workflow in which field-calibrated geomechanical models are used to define simple cut-offs, e.g. rock porosity or strength, for sand production using a combination of advanced analytical and numerical sanding models. These simple cut-offs are then incorporated in decision flowcharts to assist well engineers for completion and sand control decisions considering well-life sanding risks by following a quick, cost-effective and holistic approach. Pros and cons of pragmatic cut-offs are listed and the residual risks involved with such approaches are also highlighted. The workflow is shown in a gas field and the validity of the workflow and sand control decisions are confirmed after several years of production.

1. INTRODUCTION
Sand or solids production, also called sanding, along with hydrocarbon, water and scales is a natural component of production systems in oil and gas wells. The root cause of sanding is failure of formation rock around the wellbore due to effective in situ stresses acting on the rocks exceeding the mechanical strength under production conditions. Sanding is manageable, it can be avoided, mitigated, controlled or handled depending on its timing (i.e. reservoir pressure depletion and bottom hole flowing pressure), interval (sanding zone) and its severity (volume of produced solids, impacts of sanding on well components and well productivity). Essential parts of integrated and holistic sand management practices include; competent sanding prediction which require understanding of field geomechanical conditions, followed by sand control measures for limiting sand production to an acceptable level for both well productivity and integrity, and safety and environmental constraint. It also included consideration of sand handling and monitoring at both the surface and downhole. Sand production prediction studies are an integral part of overall hydrocarbon field development planning so that sanding potentials can be assessed and appropriate completion designs are considered.
AI-Powered Semi-Automated Trace Detection Techniques on 3D Digital Rock Mass Models
Authors: Mehrishal S. , Kim J. , Song J.-J. 
Published: August 2024

ABSTRACT:
Estimating rock mass structure relies heavily on deciphering trace lines on exposed rock surfaces. Manual detection of traces on 3D digital models can be tedious and time-consuming. This study proposes a novel AI-driven approach to enhance 3D trace surveying, overcoming potential limitations. A custom pixel-wise texture mapper algorithm transforms 3D rock models into virtual 2D images, eliminating access restrictions. DeepLabV3+, a deep-learning network, efficiently detects trace lines within these virtual images. The detected traces are transformed into 3D data through a multi-step process involving point cloud integration, thinning and segmentation, and re-projection. This meticulous reconstruction culminates in a 3D point cloud representing a trace network. This AI-powered method promises several advantages over traditional methods. Automating trace detection and minimizing human subjectivity enhances accuracy and reduces surveying time. Additionally, virtual image generation allows for surveying difficult-to-access outcrops or overcoming camera positioning challenges. Beyond the proposed methodology, the study will compare the performance of AI and human experts in trace pattern detection. Furthermore, it will explore potential applications of this technology in various geological contexts, paving the way for future advancements in rock structure analysis.

1. INTRODUCTION
Manual rock discontinuity surveys, typically relying on handheld devices, face inherent drawbacks: difficulty, time consumption, safety hazards, and surveyor subjectivity (Ferrero et al., 2009; Franklin et al., 1988; Priest & Hudson, 1976). In response, remote surveying techniques emerged, generating 3D models through dense point clouds or textured mesh models (Assali et al., 2014). Recent advancements in computational methods have empowered the analysis of these models, promising a more accurate and detailed understanding of rock mass geometry (Battulwar et al., 2021).
Algorithms leveraging 3D rock mass models offer solutions to traditional survey limitations, including challenging access, lengthy procedures, and surveyor bias. They enable significantly increased measurement volumes on rock outcrops, covering inaccessible areas with minimal effort (Ferrero et al., 2009). Moreover, automated analysis of rock faces using 3D models presents cost-effectiveness in terms of operational expenses and time compared to traditional surveying (Slob et al., 2005).
AI-Driven Predictive Maintenance for Enhanced Reliability of Top Drive Thrust Bearings
Authors: Benarbia A. , Ghachi S. , Khalifa H. , Tomomewo O. S. 
Published: August 2024

ABSTRACT:
The maintenance of the thrust bearing in the Top Drive system is important for modern drilling operations. The bearing's role is to support the drill string and ensure efficient drilling processes. However, Operational stress often leads to wear and tear, resulting in significant consequences including unexpected downtimes and compromised safety, as well as bearing failures that come with costly repairs and operational delays. These issues raise the critical need for regular and proactive maintenance strategies to mitigate risks and ensure safety. Despite the recognized need for meticulous maintenance, there exists a gap in effectively predicting the health of these bearings to prevent failures. To address this gap, our study aims to evaluate the effectiveness of machine learning algorithms, using XGBoost and Random Forest, in predicting the health status of the thrust bearings. We conducted simulations to gather data to be able to study the potential of these algorithms to facilitate automatic monitoring and detect defects. The results indicate that machine learning can significantly enhance the predictive maintenance of thrust bearings, with XGBoost achieving a leading accuracy of 97.17%, followed by Random Forest at 93.09%. The implications of our findings are profound, offering a pathway to more reliable and efficient drilling operations through enhanced preventive maintenance that implement machine learning models.

1. INTRODUCTION
A top drive is a mechanical device on a drilling rig that provides clockwise torque to the drill string to drill a borehole. It is an alternative to the rotary table and Kelly drive (Boyadjieff, 1986). The top drive is located at the swivel's place below the traveling block and moves vertically up and down the derrick.
The role of a top drive in drilling is multifaceted. King and Douglas (1995) highlight the efficiency gains and safety improvements achieved with the adoption of Top Drive systems in modern drilling operations, they enhance drilling efficiency by allowing the drilling rig to drill longer sections of a stand of drill pipe in one operation. A rotary table type rig can only drill 30-foot sections of drill pipe whereas a top drive can drill 60–90-foot stands, depending on the drilling rig size (Mahmud, and Elmabrouk, 2016).
Changes in Seismicity, Stress, and Stress Proxies Before and After the Large Seismic Event with Mw 4.2 on May 18, 2020 in Kiirunavaara Mine (Sweden)
Authors: Dineva S. , Dahner C. , Beck D. , Agostinetti N. P. , Mihaylov D. , Guclu I. E. 
Published: August 2024

ABSTRACT:
An unusually large event with moment magnitude MW 4.2 occurred on May 18, 2020 in Kiirunavaara Mine (Sweden), followed by very intense aftershock activity for about 2 weeks. A comprehensive interdisciplinary study found that the event was the result of a combination of stress, rock stiffness, strength, structural and mining factors.
In this paper, we concentrate on the observed patterns of seismic source parameters, inferred seismic velocity, and inferred stress and strain changes before and immediately after the large event, to appreciate potential warning signs for future similar events. The observations of the relation between investigated source parameters - apparent stress, energy index and seismic velocity changes - and calibrated stress and strain change from a calibrated mine scale numerical model, add to the understanding of system changes during the event and may assist in future to infer the stability state of parts of the mine, and potentially to identify some emerging instability hazards.

1. INTRODUCTION
The Kiirunavaara Mine is a Sub-Level Caving (SLC) mine located in the north of Sweden, currently producing 25 Mtones crude iron ore per year. The production areas span ∼4 km along strike with footwall to hangingwall width varying from 30 to 150 m (Figure 1). The mine is divided into 10 production areas (blocks) along the strike, numbered by the central Y-coordinate.
The mine was declared significantly seismically active after a 2008 seismic event in Block 19 (22) which caused significant damage across sub-levels from 907-964 m. Today, the mine has one of the world's largest underground seismic systems with approximately 250 geophones (Figure 1) covering the production areas with a typical magnitude of completeness of the seismic system of around ML -1.5 (Dineva and Boskovic, 2017).
This study aims to continue the seismological investigation of the M 4.2 event, looking at long- and short-term changes in patterns of seismicity and quantitative seismological measures such as energy index, cumulative seismic moment and apparent stress, and relate them to numerical modeling results. The work also aims to progress the integration, in the mine's workflow for observational management of seismic hazard, of calibrated numerical modelling forecasts of stress with quantitative seismological parameters and seismic wave velocity changes inferred via passive tomography.
A New Finite Element Code for Thermo-Hydro-Mechanical Coupling in Geomechanics: Application to Deep Borehole Disposal of High-Level Radioactive Waste
Authors: Yoo H. , Min K.-B. 
Published: August 2024

ABSTRACT:
A new finite element code was developed for modeling thermo–hydro–mechanical coupled processes in continuum-based geomechanical applications. The development was conducted using open-source software and libraries for input of model geometry and mesh, numerical calculation, and data management to take advantage of the accessibility and flexibility of the source code for updates and revisions. Implemented primarily with the PETSc library for parallel mesh discretization and numerical solvers in C++, the code incorporates physics models including heat transfer, Darcy's flow and storage, and linear elasticity and their coupled processes. The physics models were verified by comparing them with analytical solutions and a commercial FEM code. The code was applied to the simulation of deep borehole disposal for high-level radioactive waste, modeling the generated thermal stress due to decay heat emitted from spent nuclear fuels. The simulated results of changes in coulomb failure stress and ground uplifts in the deep borehole disposal model were compared with those of the reference disposal concept. This study demonstrates the applicability and future extensibility of the new finite element code to field-scale geomechanical applications.

1. INTRODUCTION
Thermo-hydro-mechanical (THM) coupled processes are a key behavior in geomechanical applications such as nuclear waste disposal in geological media, underground CO2 sequestration, and enhanced geothermal systems. Understanding the complex interaction between heat transfer, fluid flow, and mechanical responses in porous media is essential for accurately analyzing and predicting the long-term performance and safety in subsurface environments. Numerical modeling can improve the understanding of complicated coupled processes by capitalizing on the benefits of advanced computer technology.
The active development of open-source software for numerical computation as well as pre- and post-processing has facilitated the emergence of large-scale projects aimed at developing numerical simulators for coupled processes in subsurface environments. Notable examples include OpenGeoSys (Bilke et al., 2022), MOOSE (Lindsay et al., 2022), PFLOTRAN (Lichtner et al., 2020), and PyLith (Aagaard et al., 2023). The development of open-source frameworks offers several advantages, including easy access to the source code and, thus, flexibility in writing and revising the code suitable for specific needs. Furthermore, another significant advantage is the ability to obtain independent simulators from commercial software.
Research on Fracture Characteristics of Supercritical CO2 Fracturing Hot Dry Rock Based on THMD Coupling
Authors: Liu Mingsheng , Wang Haizhu , Zhang Xu , Fan Xuhao , Wang Bin , Tian Ganghua , Yi Yonggang , Stanchits Sergey , Cheremisin Alexey 
Published: August 2024

ABSTRACT:
Supercritical CO2 has excellent thermal properties and flowability, making it a potential replacement for water in efficient and eco-friendly fracturing of hot dry rock (HDR). This study develops a coupled model for fracture propagation, considering wellbore stress superposition, thermal-poroelastic effects, elastic-brittle failure criteria, and varying matrix porosity and permeability due to damage. The model's accuracy is validated through comparisons with analytical solutions and experiments. Research finds that supercritical CO2 fracturing creates more complex fractures with a wider temperature field influence. Thermal stress reduces the breakdown pressure by 55.53%, while CO2 contributes 5.89%. Breakdown pressure in HDR increases with CO2 injection rate due to pressure transmission, coupling, and filling effects. Fracture initiation and propagation can be divided into three stages: (1) Early stage dominated by thermally induced stress from; (2) Intermediate stage with competition between in-situ stresses and stress shadow effects; (3) Later stage controlled by in-situ stresses, extending along the direction of maximum principal stress.

1. INTRODUCTION
Hot dry rock (HDR) refers to a type of rock formation that lacks or contains minimal stagnant water and has a high temperature (usually above 180°C). It is an important component of geothermal resources (Zhu et al., 2015). HDR contains significant geothermal energy that can be harnessed for power generation and heating, serving as a renewable and environmentally friendly energy source. In comparison to other renewable energy sources like wind and solar, HDR geothermal resources offer advantages such as stability and freedom from seasonal and diurnal limitations (Armstrong et al., 2016). Therefore, the efficient and safe development of HDR plays a crucial role in achieving sustainable energy. HDR mainly consists of metamorphic or granitic rocks characterized by dense structures and extremely low permeability, making it challenging to exploit thermal energy through natural fractures and rock matrix permeability (Olasolo et al., 2016). Hence, engineering methods are required to transform the HDR reservoir and create a complex network of fractures, providing efficient pathways for heat transfer to the working fluid.
Molecular Dynamics Modeling of Effects of Water and Temperature on Rock Strength
Authors: Liu Li , Li Xinlong , He Wenhao , Zhang Runqing , Li Yongxin , Fan Gaojian , Ji Ran , Shi Huaizhong , Xiong Chao 
Published: August 2024

ABSTRACT:
The mechanical properties of reservoir rocks are of great significance to the study of rock mechanics, hydraulic fracturing design and reservoir stimulation. The failure mechanism and characteristics of rock under the condition of high temperature hydration have been one of the difficult problems for many scholars. In order to solve this problem, a Molecular dynamics model is used to analyze the mechanism of rock strength degradation. The compressive strength, tensile strength, Young's modulus and Poisson's ratio of quartz crystals with different water content and temperature were quantified using uniaxial tensile and uniaxial compression simulation experiments based on the established single crystal molecular model of quartz. The simulation results show that hydration and high temperature degradation have significant effects on the mechanical strength of rock, and hydration is a major factor leading to the decline of rock strength. In addition, temperature and external loading force make the internal structure of the crystal looser by changing the bond length between Si and O atoms and the angle of Si-O-Si bond. It is also found that the presence of tensile stress will change the distribution of water molecules in the interlayer, making water molecules adsorbed on both sides of the quartz surface.

1. INTRODUCTION
With the continuous improvement of oil and gas exploration and development technology, oil and gas exploration and development gradually changed from conventional oil and gas reservoirs to unconventional oil and gas reservoirs[1-2]. As an important unconventional oil and gas resource, tight sandstone reservoir has become a new field of increasing oil and gas reserves and production. Tight sandstone generally has the characteristics of low porosity and low permeability[3], and is more compact than ordinary sandstone, so it needs to be reformed by hydraulic fracturing[4]. Previous studies have shown that the mechanical properties of reservoir rocks are the key factors to determine the fracturing effect besides fracturing parameters and reservoir temperature[5-6]. Therefore, understanding the mechanical properties of reservoir rocks is the key to increase oil production. Previous studies have shown that rock macro-mechanical parameters have an important impact on the study of mechanical properties of rock. However, they can not explain the fracture initiation, fracture propagation and anisotropy in the rock, so it is necessary to further study the characteristics of the rock from microscale or nanoscale[7-8].