bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Sampling Window Geometry on the Variation of Fracture Trace Density
Authors: Choi J. , Kim J. , Song J.-J. 
Published: September 2023

ABSTRACT
Sampling windows are essential tools for characterizing fracture distribution from rock exposures, yet few studies have focused on their geometry and how it affects the obtained fracture trace information. In this study, we investigate the influence of window dimension and orientation on the variation of trace density, derived by the end-point estimator, using analytic and numerical approaches. We employ rectangular, square, and circular windows for sampling the trace density of fractures with various dip angles using Monte Carlo simulations. We find that, regardless of window shape, the variation of trace density decreases as window size increases. Additionally, for rectangular and square windows, fracture dip angle affects the variation of trace density, with more impact on smaller windows. The variation is also impacted by the fracture density and fracture size. Our results illustrate that window geometry and fracture characteristics should be considered when conducting window surveys to acquire fracture data with reduced variance.

INTRODUCTION
Fracture characterization is an essential prerequisite for the analysis of rock mass behavior in both mechanical and hydraulic aspects. To describe the fracture distribution characteristics, including fracture spacing, density, size and orientation, rock exposures are investigated through window surveys by installing sampling windows upon the rock exposure and collecting data within the window.
Different sampling windows have been suggested for the purpose of acquiring various fracture data. In an early study by Kulatilake and Wu (1984), a rectangular window was used to estimate the mean number of trace midpoints per unit area. Later on, Zhang and Einstein (1998) introduced circular windows to estimate mean trace length without orientation bias, and Mauldon (1998) proposed another method for estimating mean trace length and density using convex windows. The proposed methods were applied to an outcrop in Yingxiu, China, and their results were compared (Wu et al., 2011). Song and Lee (2001) also applied rectangular and circular windows to estimate trace length distributions, and reported comparisons between the two types of windows.
The High Temperature-Mine Thermal Energy Storage (HT-MTES) Project in Bochum, Germany
Authors: Hahn F. , Klein S. , Güldenhaupt J. , Seidel T. , König T. 
Published: September 2023

ABSTRACT
The aim of the German HEATSTORE sub-project has been the development of a mine thermal energy storage (MTES) pilot plant for the energetic reuse of an abandoned small colliery below the premises of the Fraunhofer IEG in Bochum, Germany. In the summer 2020 three wells have been drilled into existing open mine voids from the IEG drilling site. During the winter of 2020/2021, a first MTES test operation has been carried out. The underground temperature has been recorded before, throughout and after a test operation by Distributed Temperature Sensing (DTS) as well as groundwater temperature and pressure loggers, which had been installed into the MTES wells. In spring 2021, a local district heat network (DHN) has been built up at the case study site. In summer 2021, a Concentrated Solar Power plant (CSP) as the future renewable heat source has been successfully erected at the demo site and was connected to the MTES via a common heat exchanger.

INTRODUCTION
The fundamental transformation of energy supply systems in Germany by 2050 represents an immense technological and economic challenge. The German government is focusing on the increased use of renewable energies and also the efficient use of energy. Based on this strategy, thermal energy storage systems represent an important foundation for the increased use of renewable energies. The transition to a sustainable energy supply requires the provision of large electrical as well as thermal storage capacities. The potential of volatile renewable energy sources can only be fully exploited through flexible management of the electricity and heat supply networks and a wide range of different storage technologies.
The aim of this research project was to establish a pilot plant for seasonal heat storage within the former and no longer accessible IEG small colliery, which is located under the drilling site of the Fraunhofer Institute for Energy Infrastructures and Geothermal Energy (IEG) in Bochum, Germany. For this purpose, a numerical model of the former IEG small colliery was created within the HEATSTORE project and calibrated and validated by drilling three wells (MP1, MO1 and MI1) inside the mine workings of the IEG small colliery down to a depth of 64 meters. Within the scope of the project the wells were coupled with an above-ground solar thermal system.
Numerical Modeling of Cracking Behaviors of Coal Reservoirs Subjected to Cryogenic Shock
Authors: Han Songcai , Yan Xinchuang , Li Lile , Wang Lei , Yang Liang , Wang Rui , Gao Qi , Yang Junchao , Shi Xian 
Published: September 2023

ABSTRACT
Thermally-induced cracking has attracted extensive attention in improving reservoir permeability. In this paper, a thermo-elastic coupling model incorporating the strain-based elastic-brittle damage theory is used to analyze the cracking behaviors of the coal reservoir subjected to cryogenic liquid nitrogen shock. The evolution of temperature and thermally-induced stress with damage is analyzed. The effect of different factors including in-situ stress difference, elastic modulus, thermal expansion coefficient, thermal conductivity and quenching temperature on the induced crack morphology is investigated. It is found that the failure mechanism of the coal rock during cryogenic shock is mainly dominated by elastic brittle tensile damage. The induced fracture morphology is more sensitive to elastic modulus and thermal expansion coefficient relative to in-situ stress difference and thermal conductivity. The increases in elastic modulus and thermal expansion coefficient will bring about more fractures with greater complexity. The higher in-situ stress difference or lower thermal conductivity can generate more short thermal fractures. The critical quenching temperature for inducing thermal cracks around the wellbore is between −110 °C and −105 °C. The results of this study can provide some guidelines for cryogenic fracturing in coal reservoirs.

INTRODUCTION
Coalbed methane (CBM) reservoirs have the characteristics of low permeability and low porosity. At present, hydraulic fracturing is still the most widely used stimulation technology to improve the overall permeability of unconventional oil and gas reservoirs, including CBM, shale gas and tight gas (Montgomery et al., 2010; Kumari et al., 2018; Ma et al., 2021). However, hydraulic fracturing will bring about a series of thorny problems, such as high fracture initiation pressure in hard formation, pore plugging and water locking effect in water sensitive formation, serious waste of water resources, treatment of flowback fluid and environmental pollution. Compared with hydraulic fracturing, cryogenic liquid nitrogen (LN2) waterless fracturing can overcome these negative problems (Gregory et al., 2011; Rozell et al., 2012, Hung et al., 2020). The representative advantage of LN2 fracturing is that the low temperature LN2 with a boiling point of −195.8 °C produces a huge temperature difference in the rock (Jacobsen et al., 1986), resulting in tens of MPa of thermal stress. In addition, hundreds of times of the gas-liquid ratio of nitrogen also plays an important role in rock cracking. However, because of its high risk of vaporization, it is necessary to control the pressure in the wellbore through the safety valve, thus weakening the effect of nitrogen expansion-induced fracturing (Cha et al., 2018).
Review of Recent Research Related to Ultrasonic Technologies for Well Productivity Enhancement
Authors: Mierez Jesus , AlTammar Murtadha J. , Alruwaili Khalid M. 
Published: September 2023

ABSTRACT
In the last two decades, ultrasonic (US) technologies research has increasingly earned attention for applications in the oil and gas industry. Numerous laboratory and field studies have proven ultrasonics as an efficient, sustainable, and cost-effective technology for improving well productivity. This paper pursues the elaboration of a review of the most recent research related to ultrasonic technologies for applications in the oil and gas industry. The huge gap between numerical and field studies in comparison with laboratory studies deems it necessary to increase efforts on developing numerical models and field tests of the ultrasonic effect. A review of the US mechanisms for enhanced oil recovery (EOR) and emulsification/demulsification was conducted. Cavitation and thermal effects on wellbore fluid and formation rock have been widely accepted as two of the most influencing mechanisms. Most authors agreed that ultrasonics is a highly efficient method for EOR and emulsion treatment if the optimal conditions are identified and achieved. Treatment with ultrasound waves has shown improvement of oil recovery efficiency rates of over 90% and viscosity reduction values of over 80%. The most efficient results were observed when in combination with another conventional EOR method, where ultrasound boosts the recovery efficiency.

INTRODUCTION
Current oil well stimulation methods, such as acid stimulation, are in many cases ineffective and might cause additional operational issues such as emulsion formation, secondary chemical reactions, among others. These methods also involve the use of dangerous contaminants jeopardizing the facilities, personnel, and the environment. Emerging new technologies such as ultrasound stimulation present numerous advantages compared to conventional methods required by the Oil & Gas (O&G) industry to perform maintenance operations and oil well stimulations.
The present work intends to perform a comprehensive review of the available literature gathered regarding existing laboratory studies and field tests of ultrasound technology.
Previous work covered state of the art summaries for research related to ultrasound with quite specific scopes and timelines. The current work intends to continue previous researchers’ efforts with a wider focus integrating these publications, analyzing the most prominent applications for ultrasound technologies, and compiling a global summary with the latest publications and trends in ultrasonics and sonochemistry research.
Effect of the Biot Coefficient in the Dolomite Acid Stimulation Process
Authors: Cunqi Jia , Saif Alkaabi , Kamy Sepehrnoori 
Published: September 2023

ABSTRACT
Carbonate reservoirs are very important for the petroleum industry. Acid stimulation is one of the practical techniques for effective development of carbonate reserves. This study is motivated to study the effect of the geomechanical process on the acid stimulation process. In this work, an improved two-scale continuum model describing the mass, momentum, and energy change is used to investigate the acid stimulation process coupling the geomechanical process. Results show that a typical acid stimulation curve of acid consumption volume can also be observed with gemechanical process, in which acid consumption volume obtains a minimum value with a certain acid injection rate. When the acid injection rate changes from this optimum acid injection rate, more acid solution is consumed for achieving a breakthrough. But as for the comparison of the acid consumption volume with and without geomechanical process, no obvious difference is found. Introduction the geomechanical process has little influence on the acid stimulation process.

INTRODUCTION
Carbonate reservoirs are important in the oil industry as they contain more than 60% of conventional oil reserves and 40% of gas reserves (Jia et al. 2021a). Carbonate rocks are composed of at least 50% carbonate minerals, usually calcite and dolomite. These rocks provide challenging characteristics such as strong heterogeneity and double porosity, which are a result of the formation process. During oil and gas production, particles eroded from the reservoir accumulate near the wellbore region and consequently reduce permeability (Jia et al. 2015, Tian et al. 2018, Tian et al. 2021, Li et al. 2022, Li et al. 2023a, Li et al. 2023b). Acid stimulation is a common technique to increase permeability near the wellbore by injecting acid (usually HCl) to dissolve and create conductive channels called wormholes (Jia et al. 2021c). These wormholes provide high permeability channels that bypass the damaged zone near the wellbore.
Methodology for Determination of Orthotropic Strength Parameters and Principal Directions from Laboratory Testing
Authors: Loken M. C. , Johnson J. C. 
Published: September 2023

ABSTRACT
The Sanford Underground Research Facility (SURF, formerly known as DUSEL) is a dedicated underground scientific research facility located in Lead, South Dakota, at the former site of the Homestake gold mine. The SURF mission includes the construction of large underground excavations, at depths of about 1500 meters (m), to house large-scale physics experiments. A rock mechanics concern is the stability of these large-diameter (165 m) openings being constructed in the host formation mine rock that has been characterized with orthotropic material properties. The in-situ stress has also been measured at the mine and reported in the literature. The focus of this paper is on the orthotropic strength of the intact mine rock that is developed using laboratory strength data obtained from the literature. The objective of this paper is to present the theoretical development and implementation of the equations that define two- and three-dimensional orthotropic strength. The equations are developed using laboratory strength data on intact rock specimens. The method is validated using three numerical examples and applied to a data set of test results performed on mine rock specimens to determine the orthotropic strength parameters and the principal directions.

BACKGROUND
Loken and Johnson (2022) studied orthotropic elasticity on amphibolite and rhyolite rocks at the Homestake mine. The conclusion from the study was that the rocks were not elastically orthotropic because of the variation in each of the orthogonal directions was greater than the calculated orthotropy in the laboratory test results in the three mutually perpendicular orientations. Therefore, the mine rocks were assumed to be elastically isotropic where E = 70 GPa.
In-situ stress measurements taken at the Homestake mine was also examined by Loken and Johnson (2022). The conclusion from the study was that the in-situ stress state at Homestake mine has the major principal in-situ stress being vertical and the two horizontal principal stresses being approximately equal and somewhat less in magnitude than the vertical principal stress. The compressive (+) vertical stress is consistent with gravity loading where σz = 47 MPa and σx = σy = 38 MPa at a depth of 1500 m. Loken and Brosnahan (2010) investigated the Homestake mine orthotropic rock mass strengths based on laboratory testing by Duan (1985) and theoretical work by Pariseau (1972) where an orthotropic rock strength yield surface was given with the following equations in terms of nine rock property constants (H, F, G, U, V, W, L, M, N).
Study on the Integrity of Full-Well Cement Sheath During Hydraulic Fracturing of Shale Oil Well
Authors: Lu Z. Y. , Wang D. , Li J. , Xie S. Y. , Wang X. G. , Zhang H. , Song L. , Lian W. 
Published: September 2023

ABSTRACT
During the hydraulic fracturing of shale oil wells, the cement sheath is faced with the problem of integrity failure, which easily induces sustained annular pressure and affects normal production. Therefore, taking the shale oil well in the Jimsar area of China as an example, the calculation model of the full-well cement sheath stress is derived based on the theory of elasticity. The reliability of this model was verified by the finite element method. This paper calculates the full-well cement sheath stress distribution and analyzes the cement sheath failure zones and influencing factors in hydraulic fracturing. The results show that the shallow cement sheath is primarily in tensile failure, and the deep cement sheath is primarily in compression failure. Using high Poisson's ratio cement above the surface casing shoe and low elastic modulus cement below the surface casing shoe, along with increasing the wall thickness of the production casing, will help reduce the failure length of the cement sheath. The study results have important implications for controlling wellbore integrity in shale oil wells.

INTRODUCTION
Multi-stage hydraulic fracturing technology for horizontal shale oil wells is vital to improve reservoir conditions and increase shale oil production capacity (Wang et al., 2012; Zhang et al., 2015; He et al., 2021). Multi-stage hydraulic fracturing is characterized by large discharge volume, high pressure, and long operation time, which leads to a harsh casing-cement sheath service environment and easily induces wellbore integrity problems (Lian et al., 2002; Tian et al., 2015). Of the 15,000 wells tested in the Gulf of Mexico, approximately 43% experienced cement ring integrity problems during completion, ultimately resulting in sustained annular pressure (Muehlenbachs, 2011; Vengosh et al., 2014). Similar problems existed during shale oil development in the Jimsar area of China. The cement sheath integrity problem during hydraulic fracturing severely restricts large-scale development activities in shale oil fields.
The cement sheath stress is closely related to the service environment. During the fracturing of shale oil horizontal wells, the internal casing pressure, formation properties, and in-situ stress conditions vary at different depths, which affect the cement sheath stress and failure risk (Liu et al., 2017; Xi et al., 2018). Therefore, revealing the full-well cement sheath stress state in horizontal shale oil wells during hydraulic fracturing and elucidating the main controlling factors of cement sheath integrity failure are of great significance to controlling the wellbore integrity of shale oil wells.
Subjectivity in Crack Initiation Measurements Using Conventional Stress-Strain Based Methods
Authors: Koosmen K. , Wang T. , Asche H. , Serati M. 
Published: September 2023

ABSTRACT
Stress-strain based methods are frequently adopted in the literature to estimate crack initiation (CI) strength in rock. However, despite their widespread use, these methods can introduce subjective interpretations of the stress-strain curves, particularly in rocks with pre-existing microcracks or high porosity. This study aims to examine the subjectivity inherent in strain-based methods and its potential impact on consistent measurement of rock CI. A survey is then conducted using experimental data obtained from sandstone and granite specimens. Results suggest a wider scatter of CI values for sandstone samples, which aligns with expectations due to their inherent pore structure heterogeneity. The Lateral Strain Response (LSR) method demonstrates the least coefficient of variation, indicating less subjectivity. Further research and validation is recommended to improve confidence in the LSR method using parallel measurement techniques.

INTRODUCTION
In rock engineering, the crack initiation (CI) stress threshold refers to the stress level where new microcracks start to develop within the rock matrix. In practice, it has been demonstrated that the CI stress level can be used to estimate the strength of rock against spalling and rockburtst type failures in deep underground excavations (Martin, 1997; Diederichs, 2007). Further, the CI stress also provides an indication of the stress conditions where breakout can occur in boreholes and petroleum wellbores. The CI stress is usually recognised to be around 30 to 60% of the peak value measured during an Unconfined Compressive Strength (UCS) testing (Brace et al., 1966, Bieniawski 1967, Holcomb & Costin, 1986; Cai et al., 2004; Nicksiar & Martin 2013, Wen et al., 2018)
There is a wide range of methods that are available to estimate the CI stress which includes several strain-based methods (SBMs), acoustic emissions (Keshtgar & Modarres, 2013), electrical resistivity (Lataste et al., 2003), digital image correlation (Dong & Pan, 2017), optical diffraction patterns (Li et al., 2002), laser speckle interferometry (Ennos, 1975), and ultrasonic probing (Mi et al., 2006). The strain-based methods are most common due to their low cost and simplicity (Mutaz et al., 2020). With these methods, the CI stress is interpreted from a characteristic change in the stress-strain response that is measured during compression loading.
Seismic Performance of a Large Underground Cavern at Different Excitation Direction
Authors: Zhu Yimo , Zhang Qianbing 
Published: September 2023

ABSTRACT
Underground infrastructures can be adversely affected by earthquake-induced rock engineering vibration causing damage problems. These impacts are even more significantly affected for large underground caverns due to the large span and complex structures. Currently, time-history numerical simulation is still the most popular method for seismic design of underground infrastructure, however it is based on the plane-strain model and assumes the vertical incidence of seismic waves. In fact, the propagation direction of seismic wave is arbitrary and the effect of excitation direction has not been understood well. In this paper, a 3D full-scale hydropower station is built by FLAC3D, and several sets of seismic waves based on the real earthquake motions are applied from different excitation direction. The results show that the wave excitation direction directly influences the result of the large underground cavern assessment, which is manifested by traditional vertical wave applied at bottom underestimating the response, especially for the cases of high lateral stress.

INTRODUCTION
Underground infrastructures are being built at a fast rate to meet the expanding space needs of densely populated urban areas and megacities. Australia is witnessing historic investment across transport, utilities, and social infrastructure. In total, more than $300 billion of major transport projects will be delivered in the next 10 years. The two major subsectors within transport (road and rail) account for around 75% of total Major Public Infrastructure Pipeline resource demand. There will be a 25% increase in tunnelling projects in the next five years (Infrastructure Australia, 2022). Considering the future development scale, existing project volume, unit construction cost and the important role of these infrastructures in modern society, even minor earthquake effects and related downtime may lead to significant direct and indirect losses, for example, In 2021, an earthquake (M5.9) hit near the town of Rawson, which is the biggest earthquake on record in Victoria. About every ten years or so, Australia experiences a potentially damaging earthquake of magnitude 6.0 or more (Geoscience Australia, 2021). In 2023, the central-southern turkey hit by two more powerful earthquakes (M6.4 and M5.8) two weeks after disaster (M7.8 and M7.5), destroying railway infrastructure there, including 446 bridges, 6161 culverts and 175 tunnels (Thomas Johnson, 2023), damaged roads, border crossings and critical infrastructure, severely hampering aid efforts (Elias A.A., 2023). Therefore, it is essential to carefully consider the impact of seismic loads on tunnel design, construction, operation and risk assessment.