bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative Study on Enhanced Oil Recovery Effect of Amphiphilic Nanomaterials - Experiment and Mechanism Investigation
Authors: Li Yuan , Li Bojun , Sheng Lianqi , Yao Erdong , Zhang Kun , Yu Guolin , Zhou Fujian
Published: October 2022

Due to the transcendental property of nanoparticle, nanoparticle fluid flooding becomes one of the enhanced oil recovery (EOR) technique, which had played a significant role in tight oil exploitation in the worldwide scale recent years. In particular, the amphiphilic nanomaterials can greatly increase the oil recovery.

To provide some guidance in selecting nanomaterials for flooding, 3 kinds of amphiphilic nanomaterials, including silicon dioxide (SiO2), graphene oxide (GO) and molybdenum disulfide (MoS2), are chosen to serve as object of the study. In lab, the physical properties were systematically characterized and flooding was conducted. Further, the morphology character of nanomaterials was placed extra emphasis and the mechanisms of EOR were also studied. The purpose was to find the link between the morphology of nanomaterials and EOR. Flooding experiment revealed that MoS2 were able to enhance the oil recovery by approximately 11%, which were better that of the others. From the above, it can be inferred that spherical materials have a "point-to-surface" contact at multiphase interfaces, while sheet materials can achieve a "surface-to-surface" contact with a higher interfacial activity. In addition, the film-climbing characteristics of amphiphilic nanomaterials were found in the experiment, which may be one of the potential reasons for enhanced oil recovery.

1. INTRODUCTION

Most of the world’s oil fields have experienced primary and secondary oil recovery, with severe declines in well production and increases in water content. Combined with unfavourable conditions such as low reservoir permeability, about 50% or more of the crude oil cannot be successfully recovered (Alija et al, 2018). Chemical drive is a commonly used method to enhance recovery and is widely used in China, but with the gradual expansion of unconventional reservoir development, the main application of chemical drive has shifted to low-permeability and ultra-low-porosity reservoirs. Due to the small pore size and large specific surface area of low-permeability and ultra-low-permeability reservoirs, they have unfavourable factors such as high start-up pressure gradients and insufficient formation energy, and the development of these reservoirs is mainly based on water injection, resulting in problems such as "no injection, no recovery" in low-permeability and ultra-low-permeability reservoirs (LI Weicai et al, 2011; DOU Hong en et al, 2014; LI Xiangfang en et al, 2020). This has become one of the current issues of concern in terms of EOR.
Mapping and Characterization of Rockfall Runout Talus Deposits from Columnar Basalt Cliffs in Boise, ID
Authors: Hudyma N. , Walker N. , Chittoori B.
Published: October 2022

The Boise Valley contains several columnar jointed basalt cliffs, which were deposited approximately 1.4 to 0.5 Ma on terraces formed by downcutting of the Boise River. Three runout talus deposits on Whitney Terrace were characterized using unmanned aerial vehicle visual imagery. Although the runout talus deposits were from different areas and were of varying size, they contained roughly the same dimensions and distributions of blocks. Images of the cliff face indicated that blocks were detached from the base of columns along horizontal discontinuities which lacked support (undercut columns) and by toppling of basalt columns. The mapped block sizes in the cliff face were larger than the blocks in the associated runout, indicating the cliff blocks were fragmented during impacts in the runout.

1. INTRODUCTION

The movement of geologic materials downslope, commonly referred to as landslides, is one of the most well-known geologic hazards. Varnes (1978) developed the most widely used classification framework for landslides. Since the Varnes classification scheme was developed, various modifications have been proposed and adopted. Still, the goal is to be able to describe the movement(s) and the end result(s) of the landslide using well-known terminology which incorporates the focus of the investigators (Hungr et al., 2014).

Our focus is to characterize the runout talus deposits formed from the dislodgement and subsequent downslope movement of rock blocks from columnar basalt cliffs. Columnar basalt, or specifically columnar jointing in basalt, is a type of rock mass that is divided into long prismatic blocks. The formation of the jointing is complex and thought to be a series of events rather than simple cooling of the lava. The vertical discontinuities are continuous and horizontal discontinuities are less prominent and generally end at the edges of the vertical discontinuities (Spry, 1962).

Failures of rock masses with columnar jointing have been studied in several geographical locations, including Australia (Dahlhaus and Miner, 2000), Chile (Holm and Jakob, 2009), Spain (Abellán et al., 2011), and Washington State (Guzek, 2019). The failure mechanism most often reported in these studies has been the somewhat generic term "rockfall", even though the studies mentioned above have shown that two failure (detachment) modes occur, rockfalls and rock topples.
Prediction of Safe Drilling Fluid Density Window in X Oilfield Through an Integrated Geomechanics Approach: A Case Study of Well a
Authors: Li Huayang , Deng Jingen , Zhu Shijie , Cao Zhipeng , Wen Yuehua , Zhang Chunfang , Cai Wenjun
Published: October 2022

X Oilfield is located in the southern Bohai Sea. The formation fractures of the Neogene Minghuazhen Formation are developed. During drilling, wellbore collapse and block falling are prone to occur, and even cause stuck and stuck drilling. This paper presents a comprehensive geomechanical method which combines theoretical analysis with numerical simulation. By collecting a large number of geological, seismic, drilling and logging data, this method selects the appropriate theoretical model to predict and calculate the ground stress, pore pressure, fracture pressure, collapse pressure and rock mechanical parameters of well A, and draws the formation four pressure profile, and then obtains the safe drilling fluid density window of the well. In this paper, based on the elastic-plastic mechanics theory, the stress state of the wall rock is analyzed, and the numerical simulation of wellbore stability is carried out by using ABAQUS software. The influence of pore pressure, formation strength and drilling fluid density on wellbore stability is analyzed, which provides a powerful tool for understanding the wellbore instability mechanism of the target block of X oilfield, and effectively controls the wellbore instability phenomenon of Well A.

1. INTRODUCTION

Since the 21st century, China has gradually focused on offshore oil and gas development in the context of the gradual depletion of conventional oil resources on land. Overall, there are relatively abundant oil and gas deposits in Chinese offshore areas. China’s offshore oil and gas resources are abundant in general. In recent years, Bohai Basin has made significant oil and gas discoveries and has a good development prospect. It is the main offshore oil and gas production area in China . The target well in this paper is well A, which is located in the south of Bohai Sea. The core technology of offshore drilling and completion and the stability of borehole wall are the key issues for the smooth development of offshore oil and gas resources. The theory and research results involved in this paper can not only provide scientific guidance for well A, but also provide theoretical support for the well area of the oilfield and even for the drilling of Bohai Bay in China, which has very important engineering guiding significance.
A Coupled Hydro-Mechanical Model for Simulation of Two-Phase Flow and Geomechanical Deformation in Naturally Fractured Porous Media
Authors: Liu Lijun , Liu Yongzan , Wang Xiaoguang , Yao Jun
Published: October 2022

This paper presents a coupled fluid flow and geomechanics model for analysis of two-phase flow and deformation behaviors in naturally fractured porous media. The discrete fracture model (DFM) is used to model two-phase fluid flow. The zero-thickness interface element method coupled with a modified Barton-Bandis’s constitutive model is applied to model the mechanical behavior of natural fractures. The finite volume (FVM) and finite element (FEM) methods are used for the discretization of flow and geomechanical equations, respectively. The coupled problem is iteratively solved using the fixed-stress splitting algorithm. Then the proposed model is applied to investigate the two-phase fluid flow in fractured porous media under various in-situ stress conditions. The results show that fracture aperture significantly increases as the differential stress increases due to shear dilation, which accordingly enhances the equivalent permeability of the fractured medium. Channelized flow is formed through the dilated fractures, which results in early water breakthrough and reduces the water sweep efficiency. This study illustrates the importance of shear dilation on two-phase flow behaviors in fractured porous media and highlights the necessity of considering shear dilation for accurate prediction of saturation distributions. The simulations also demonstrate the capacity of our model to capture the complex coupled behavior induced by the interaction between pore pressure and in-situ stress loadings.

1. INTRODUCTION

Hydro-mechanical coupling in fractured media is an important issue in various engineering applications, such as oil and gas recovery (Moinfar et al. 2013; Yan et al. 2018), geothermal reservoirs (Pandey et al. 2017; Li et al. 2019), CO2 sequestration (Rutqvist et al. 2007; Cappa and Rutqvist 2011), and nuclear waste disposal (Nguyen and Selvadurai 1995; Yow and Hunt 2002). As the high-conductive flow channels and weak surfaces, fractures are often characterized by the rough surfaces, which could deform under the joint influence of normal closure and shear dilation. In particular, shear dilation may play a dominant role when rough fractures suffer certain shear displacement, which is believed to be able to significantly enhance the fracture permeability (Zhang et al. 2008).
Experimental Study of Conglomerate-Breaking Characteristics of Axe-Shaped PDC Cutter
Authors: Zhenliang Chen , Huaizhong Shi , Han Chen , Zhenquan Wang , Zhongwei Huang , Xianzhi Song
Published: October 2022

Conventional PDC cutters are prone to get broken when drilling through conglomerate formations and soft-hard interbedded heterogeneous layers, leading to serious fatigue wear, short bit life, and small bit footage. Compared to the conventional PDC cutter, axe-shaped PDC cutter can dig out gravel and pebbles through crushing and shearing, which significantly reduces energy consumption for rock-breaking. Thus, this paper proposed to study effects of axe-shaped PDC cutter cutting parameters on rock-breaking characteristics of conglomerates. Using PDC cutter cutting equipment, the research quantitatively revealed the effects of cutting depth, back rake angle, and cutting speed on the cutting force, cutting size distribution, and the groove morphological characteristics of axe-shaped PDC cutter. Also, mechanical modeling was used to describe the mechanical dynamics of the axeshaped PDC cutter in the cutting process. Then, an axe-shaped PDC bit was designed and manufactured, for the purpose of field application. According to the testing data, the cutting force of the axe-shaped PDC cutter increases with increasing back rake angle and increasing cutting depth. The larger the cutting angle, the more complicated the relationship between the cutting force amplitude and the cutting depth, from linear relation to quadratic and cubic functions. Meanwhile, the mechanical specific energy for rock-breaking remains at a small level in a cutting angle range of 10 to 20 °. Compared with the conventional PDC bit, the bit footage of PDC bit with ASP-cutter increased by 399m and the average ROP increased by 24.22%. These findings are expected to provide theoretical guidance on the rock-breaking characteristics of axe-shaped PDC cutter, especially for the drilling process in conglomerate formation.

INTRODUCTION

Since PDC bit was introduced into the oil and gas drilling industries in 1970s by GENERAL Electric of the United States, it has been widely used in drilling soft to medium-hard formations with high rock-breaking efficiency and long service life (Yang and Guo 2018). However, in the drilling process of conglomerates and other heterogeneous layers (e.g. soft-hard interbedded layers), conventional PDC cutters are easily to get broken and prone to crack, leading to premature failure of drill bit, low drilling efficiency and high drilling cost (He et al. 2021; Zeng et al. 2021).
True Triaxial Testing of Anisotropic Solids
Authors: Zhu X. , Serati M. , Mutaz E. , Chen Z.
Published: October 2022

Accurate determination of rock mechanical properties (particularly sedimentary shales, mica and schists with foliation and bedding planes) is critical to the safe design and excavation of underground mines and tunnels. Traditional techniques to calculate rock elastic properties often involve testing cylindrical or disc-shaped specimens under uniaxial compression or diametrical loading. But, these stress conditions may not represent the actual stress state under which rock is subjected at depth. A true triaxial testing technique on cubed specimens are, therefore, preferred as it better represents field stress conditions. This paper introduces and verifies a modified step-compression true-triaxial based technique to measure the elastic constants in fibre-reinforced epoxy samples, selected as a low-porosity anisotropic solid. The elastic constants obtained from the proposed method (even under higher stress levels) are found to be in good agreement with results from the benchmark tests with uniaxial compression but in the meanwhile offers other anisotropic parameters, which cannot be obtained from conventional measurements.

1. INTRODUCTION

Accurate determination of rock directional elastic properties has always been a hot topic in rock mechanics with immediate applications in most geotechnical and mining engineering (Eberli et al., 2003). While rock is frequently treated as a CHILE (continuous, homogeneous, isotropic, and linearly elastic) medium, this assumption provides only limited insight into the true rock mass deformations (Chou & Chen, 2008; Serati, Alehossein, & Williams, 2016). A more practical rock behavior is therefore the consideration of rock anisotropy, since many rocks exposed near the Earth’s surface show various levels of directionally dependent properties due to bedding, stratification, foliation, fissuring, schistosity, jointing, and faulting (Amadei, 1996).

In the stress-strain relationship study for a loaded rock sample, rock behavior can be generally classified into four categories: isotropic, transversely isotropic, orthotropic, and anisotropic. The number of elastic constants to represent the stress-strain relation of a complete anisotropic rock is 21. However, due to the elastic symmetry of three isotropic planes, the number of stiffness constants of an orthotropic material can be reduced to nine (9) constants only. It can be further reduced to five elastic parameters for a transversely isotropic material (E1, E2, ν1, ν2, and G2) and two (namely the Poisson’s ratio and Young’s modulus) for a perfectly isotropic material, where the subscripts "1" and "2" refer to in-plane and out-of-plane directions in transversely isotropic materials (Ding et al., 2006).
Experimental Determination of Poroelastic Properties of Utah FORGE Rocks
Authors: Zhou Xuejun , Ghassemi Ahmad
Published: October 2022

In this paper we present the results of a laboratory experimental study to measure the poroelastic properties of Utah FORGE reservoir rock. The target formations are granite and granodioritic rocks of low permeability so that the determination of their poroelastic properties is particularly challenging. In this work, we present the measurements of the Biot’s effective coefficient α and the Skempton’s B. The measurements on α are made by using strain gauges by following two different approaches: (1) α = 1 − K/Ks, K is the drained bulk modulus and Ks the grain bulk modulus; (2) α = −K/H, in which H is the so-called poroelastic expansion coefficient. These approaches yield two sets of data which can be compared. The Skempton’s B measurement is based on the equation α = Δpp/ΔPc|Δmf = 0, i.e., the ratio between pore pressure change and confining pressure change under an undrained condition, and distilled water is used as the pore fluid. The test results show that both the Biot’s coefficient and Skempton’s B are all stress dependent and decrease with the increase of the effective stress. Furthermore, we observe that the Biot’s coefficient falls in the range of [0.5, 1) rather than [0, 1) for many different types of rock, including the rock samples in this research.

1. INTRODUCTION

Thermal energy is extracted from the reservoir by coupled transport processes (convective heat transfer in porous and/or fractured regions of rock and conduction through the rock itself). Enhanced Geothermal Systems (EGS) generates flow pathways and heat transfer area through a variety of stimulation methods, including hydraulic stimulation to the locations that lack natural permeability (Ghassemi, 2005; 2012; Tester et al., 2006).

The Department of Energy (DOE) has established a dedicated subsurface laboratory called the Utah Frontier Observatory for Research in Geothermal Energy (Utah FORGE) in order to investigate and develop enhanced geothermal technology in 2014. The ultimate goal of the FORGE project is to demonstrate to the public, stakeholders and the energy industry that EGS technologies have the potential to contribute significantly to the future power generation (Moore, et al., 2020).
Experimental Study for the Validation of Drilling Optimization Model for Improved Performance in Hard Rock Formations
Authors: Trivedi A. , De La Fuente Valadez J. , Kandala S. S. , Mai A. , Shor R. J. , Vetsak A.
Published: October 2022

Lower Rate of Penetration (ROP) is one of the key challenges while drilling through deeper hard rock formations to access geothermal reservoirs in an advanced geothermal system (AGS). Rotary percussive drilling (RPD) becomes crucial for such systems in increasing ROP. The transferability of hammer drilling operations in deeper and harder rock formations, the mechanisms behind the improved drilling performance, and a nuanced understanding of the drilling dynamics of the method remains to be a critical challenge for a full-scale application of RPD in advanced geothermal systems. This study addresses these challenges through experimental validation of a developed bit performance index (BPI) model. The BPI model was developed using a reward function, the outcome is either rewarded or penalized. The concept of reward function usually exists in optimization and machine learning models. Using the combination of bit geometry, RPM, and hammer frequency, the function predicts optimum drilling dynamic parameters to maximize the ROP under given conditions. A series of experiments, limited to atmospheric pressure and ambient confining stress, were conducted using state-of-the-art hammer drop equipment developed in the laboratory to validate BPI, using dome-shaped diamond percussion inserts on granite rock samples. Efficiency estimates and volume removed by impacting the rock surface at different locations while moving away from the center of the crater were determined through these experiments. The results followed the BPI model – maximum efficiency and volume removal at the edge of the crater as compared with impacts at the center and center-edge. This study provides a novel approach to the characterization of drilling performance using RPD and gives a pathway for improved drilling performance through optimization of drillstring dynamics in deeper, harder rock formations for geothermal well drilling.

1. Introduction

Rotary Percussion Drilling (RPD) had been widely used in the industry, before the introduction of rotary rigs in the mid-1930s, for its potential to drill faster in hard formations like granites. In RPD, a down-the-hole hammer is driven by either air or fluid (water) through drill pipes, which also acts as a cleaning mechanism for downhole cuttings.
Improved Upscaling Methods for Carbonate Rock Image Data
Authors: Kumar Shahi Anup , Kumar Anil , Singh Kumar Hemant , Gamage Ranjith Pathegama
Published: October 2022

Volumetric image data of rocks often need sophisticated image processing steps in any rock physics and petrophysics workflow. While the segmentation is highly dependent on the quality of data, a trade-off between resolution and field of view is inevitable. This work attempts to resolve this using multiple-point statistics that have long been used for generating synthetic images, though mostly applied to sandstone rocks where the heterogeneity is significantly less than that of carbonates. These algorithms work by sequentially populating a grid to emulate the observed image. However, finding the optimum kernel parameters is crucial to capturing the spatial characteristics of the data. Also, when dealing with multiple images, finding a single set of kernel parameters might not be a trivial task. Further these methods work by computing a covariance kernel that scales as the third power with the number of training examples, thus not scaling well with the more data. Therefore, we seek to design a single image-based upscaling method that would help alleviate these difficulties. We test the proposed methodology on carbonate rock sample data which are known for their complexities at various scales. In this study images of 4 samples are considered. An upsample-deblur is developed that consistently works better than the conventional bicubic interpolation based upsampling technique. For this, a low-resolution 2D image sample is extracted from an X-ray microtomography dataset which was then subjected to a Random Forest based upsampling algorithm. It is found that the data from low scale could be improved to form a single super-resolution image. The algorithm produces an image that is always better than the bicubic algorithm. We anticipate this strategy would help design advanced algorithms where the amount of training examples is less.

1. INTRODUCTION

Digital Rock Physics workflow has gained significant attention from researchers due to its promising accuracy to characterize rocks and predict desired properties through numerical simulation (Andrä et al., 2013a, 2013b). Digital rock physics is a numerical workflow to compute and simulate various rock properties such as permeability, electrical conductivity, and elastic moduli based on high-resolution representations of the complex pore geometry obtained from imaging (Andrä et al., 2013a, 2013b; Arns et al., 2019; Devarapalli et al., 2017; Mehmani et al., 2020; Wildenschild & Sheppard, 2013).
EGS Stimulation Design with Uncertainty Quantification at the EGS Collab Site
Authors: Burghardt J. , Knox H. A. , Doe T. , Blankenship D. , Schwering P. C. , Ingraham M. , Kneafsey T. J. , Dobson P. F. , Ulrich C. , Guglielmi Y. , Roggenthen W.
Published: October 2022

Engineering a robust hydraulic connection between wells is one of the most difficult aspects of enhanced geothermal systems (EGS). Designing and constructing such hydraulic connections requires an understanding of the in-situ state of stress and the heterogeneities and discontinuities that naturally exist and may control the stimulation. Even with comprehensive stress and formation characterization programs, substantial uncertainty remains in these key parameters. This is especially the case in high-temperature EGS environments where drilling conditions are often difficult and far fewer logging and testing options are available. This paper presents a new approach for explicitly quantifying the uncertainties in the state of stress using a Bayesian Markov Chain Monte Carlo method. This approach produces a probability distribution for the stress tensor, including a general 3D orientation, that reflects the uncertainties in all the observations or indicators used to constrain the stress state. This method is demonstrated using the characterization data for the EGS Collab Experiment 2 site. The output of the analysis is used to guide the design of the planned stimulations. In the case of research projects like EGS Collab, explicitly quantifying the uncertainties in the stress state allows for more rigorous hypothesis testing by allowing conclusions drawn from the experiments to be interpreted in the context of the uncertain knowledge about conditions in the test bed.

1. INTRODUCTION

Enhanced Geothermal Systems (EGS) require use of hydraulic pressure to artificially generate fluid pathways between one or more wells. The hydraulic pressure interacts with the in-situ state of stress and rock properties to create new fractures or enhance the permeability of existing fractures. The fracturing can include contributions from both tensile (Mode I) and shearing (Mode II) displacements (e.g., Norbeck et al., 2018). One concept for creating sustainable EGS reservoirs centers on preferentially creating Mode II shearing displacements on naturally occurring fractures, which is often called shear stimulation or "hydroshearing." The potential advantage to shear-mode stimulation is that when fractures shear, they often also permanently dilate because the asperities on the fracture faces no-longer mate together perfectly after the shearing offset. This has the potential to create a fracture with significantly improved hydraulic conductivity without requiring the placement of proppant as in petroleum stimulation operations.
Relationship Between Macroporosity and Young's Modulus Through UCS Tests on Rock and Analogue Models, and Numerical Modeling – a Literature Review
Authors: Avar B. B. , Hudyma N. W.
Published: October 2022

It is well known that rock porosity reduces rock Young’s modulus of intact rock specimens. However, it is not well understood how different types and amount of macroporosity in forms of non-connected or isolated cavities (e.g., vesicular basalt, lithophysal tuff) or interconnected vugs (e.g., vuggy limestone) affect rock elastic properties. Such macroporosity leads to challenges in deriving engineering properties of rock. This paper compiles an existing database for porosity and Young’s modulus of macroporous rocks. The database includes Young’s modulus determined from unconfined compression testing on intact rock specimens and analogue specimens used to prepare rock-like test samples and numerical simulations of compression testing on similar materials. The database is used to develop the relationship between porosity and Young’s modulus. In addition to the porosity, the macropore shapes, sizes, locations, and proximity of a macropore to its neighboring macropore play a role in how porosity affects intact rock Young’s modulus.

1. INTRODUCTION

Macroporosity, which is the porosity due to visible large voids or cavities, impacts mechanical properties, such as strength and Young’s modulus (E). Examples of such rocks are primarily volcanic (e.g., vesicular basalt, lithophysal tuff, lithophysal rhyolite, pumice, and scoria) and sometimes sedimentary (e.g., vuggy limestone and coquina). Engineering characterization of such rock is challenging due to macroporosity variation within the rock mass, distribution (void-to-void proximity, void alignment), and shape of the macropores (Jespersen et al., 2010; Davis et al., 2017). Preparing test specimens of standard sizes from rock cores or outcrop blocks can be difficult due to macroporosity. Obtaining a representative specimen is also challenging as the size of the macropores becomes too large to prevent large macropores from being sampled. For example, the lithophysal tuffs of Yucca Mountain, Nevada, had macropores ranging in size from approximately 1 to 50 cm, with a maximum size up to 1 m (CRWMS M&O 2000). When laboratory compression tests are carried out on these limited number of specimens, the distribution of data is typically scattered.
Laboratory Test on Direct Shear Behavior of Rock Joints Using a Bar Drop Impact System
Authors: Kim G. G. , Shin C. H. , Jeon P. R. , Lee S. G. , Kim H. R. , Min G. J. , Cho S. H. , Yang J. S. , Yun K. J.
Published: October 2022

For an underground excavation at depth in highly stressful conditions, it is important to mitigate the risk of stress-induced failure, e.g., rockburst, and improve miner safety concerning the stability of underground workplaces and the prevention of fatalities. In general, the cause of rockburst is classified into three categories: strainburst due to stress-induced fracturing, rock ejection by seismic energy transfer, and rockfall associated with mining-induced seismicity. In this study, the Split Hopkinson Pressure Bar (SHPB) modified configuration of bar drop apparatus was developed by attaching a direct shear test box and a long bar. As a result, the modified bar drop system enabled to replicate and control of a seismic velocity that was an incident on the joint rock surfaces installed in the direct shear testing box. The long bar installed in the modified bar drop system provides a longer stress wavelength to overcome the relatively shorter duration of the stress waves in the SHPB system. The dynamic shear test on the jointed rock samples using the bar drop apparatus also provided the information to estimate the rock joint shear strengths.

1. INTRODUCTION

The rock structures stability depends on the distribution characteristics and mechanical characteristics of discontinuous surfaces such as faults and joints in the rock. Underground excavation has high-stress conditions, and such workplaces are causing stability and fatalities of underground workplaces due to rockburst. In general, the cause of rockburst is classified into three categories: strainburst due to stress-induced fracturing, rock ejection by seismic energy transfer, and rockfall associated with mining-induced seismicity. In order to understand the behavior and stability of such rock structures, it is necessary to understand the shear characteristics of the joint surfaces.

The direct shear test and multi-stage shear test are methods to measure the shear characteristics of the joint surfaces. The direct shear test measures the shear characteristics of a joint surface by generating shear displacement with different load conditions from each specimen and requires samples with the same roughness. However, it is difficult to obtain samples with the same roughness in the field, so a multi-stage shear test is conducted. A constant normal load section is set as a specimen in the multi-stage shear test. The shear characteristics for each normal stress stage are measured by generating shear displacement while increasing the normal load. In the case of the multi-stage shear test, the International Society of Rock Mechanics and Rock Engineering (ISRM, 1981) recommends the discontinuous surface test method for rock. However, it has been pointed out that the joint surface of the specimen is damaged due to an increase in shear load due to the normal load, resulting in a lower shear strength than the direct shear test (Zhao and Zhou, 1992).
Simulation-Based Patterns Optimization of Enhanced Geothermal Systems
Authors: Porlles J. W. , Jabbari H.
Published: October 2022

We developed a workflow to generate sensitivity analysis and optimization of an Enhanced Geothermal System (EGS) with vertical and horizontal wells in different patterns. The recovery factor, heat extraction, and NPV (Net Present Value) of each pattern were determined as a part of the sensitivity analysis. This study models a conceptual reservoir geometry and tries to answer questions related to injection patterns, reservoir parameters, and type of reservoir, and contribute with additional knowledge about how to improve an EGS. Hence, an optimal thermal flow rate that makes the most of NPV was calculated. A sensitivity study on the controlling parameters such as porosity, horizontal permeability, vertical permeability, natural fracture spacing, thermal conductivity, and thermal capacity to determine how these parameters affect the heat extraction of the reservoir was developed. A complete economic analysis of the electricity generation value was assessed from several scenarios with current electricity prices and drilling costs.

1. INTRODUCTION

We generated a sensitivity analysis and optimization to evaluate how different parameters and patterns impact an EGS project economically, modeling some patterns of horizontal wells and vertical wells. The assessment covers a conceptual and simple representation of the reservoir. The purpose is to evaluate relationships between initial energy in situ of the rock and water. This evaluation was compared with the energy produced, considering a full economic analysis such as NPV, discount rate, reservoir temperature, number of horizontal and vertical drilled wells, depth, and electricity sale price. EGS is a significant opportunity to reconsider geothermal energy as a part of the next transition energy. EGS is located significantly deeper than conventional geothermal wells, between 2.7 Km to 5.5 Km; this depth is required to stimulate the rock, creating an artificial circulation system and developing a hydraulic fracturing (HF) or hydro-shearing (Gischig and Preisig, 2015). The hydraulic fracturing technique generates artificial fractures to improve the flow rate of an EGS project.
Production Enhancement with a New Acid in Tight Sandstone Reservoirs: Accelerating Guar Breaking and Minimizing Formation Damage
Authors: Zhang Mengchuan , Liang Tianbo , Bai Hao , Li Bojun , Wang Qing , Yao Erdong , Zhou Fujian , Liu Wei
Published: October 2022

Crosslinked guar is suitable for the stimulation of thick tight sandstone reservoir, which can enhance the height and length of propped fractures. However, conventional gel breakers can leave residues that causes formation damage. Acid can accelerate the gel breaking rate, but it may cause secondary precipitation damage after reacting with the reservoir rock. In this study, a new acid with a low reaction rate, chelating effect, and high gel breakage is developed that can enhance the conductivity of created fractures by minimizing gel residues and inhibiting secondary precipitations after acidification. The breaking rate of the crosslinked guar by a conventional gel breaker and the new acid is compared, during which the viscosity of the solution, the molecular weight, residues, and the change of pressure with time before and after displacement damage are measured with time. The results show that the gel breaking speed of adding new acid is twice that of adding conventional gel breaker. The average relative molecular weight of the polymer in the gel breaker is reduced by 20%, and the median particle size is less than 50 μm. The permeability recovery rate of adding the new acid is much higher than that of adding conventional gel breaker. The content of metal ions in the flowback liquid is much higher than that of the initial control sample, indicating that the acid system contains chelator has a better ability to inhibit secondary precipitation. Field test shows that the average daily oil production of a single well reaches 30 tons/day after the new acid is used.

1. INTRODUCTION

Tight sandstone reservoirs are widely distributed, such as San Juan basin in the United States, Alberta basin in Canada, Ordos and Tarim Basin in China. Tight sandstone is defined as permeability less than 0.1 × 10−3 μm1 2 (Law et al., 1986). It is mainly caused by the massive precipitation of authigenic clay minerals, the crystallization of cement, and the change of primary pores. Compared with conventional reservoirs, tight sandstone has the characteristics of extremely low porosity and permeability, sensitive permeability to stress and high bound water saturation, and has fracture structures such as microfractures, cleavage fractures, and bedding fractures (Shanley et al., 2004).
Impacts of Variations of the Minimum Horizontal Stress on Hydraulic Fracture Growth and Microseismicity
Authors: Kohli A. , Zoback M. , Singh A.
Published: October 2022

Hydraulic fractures propagate when fluid pressure overcomes the minimum horizontal stress. Variations of the minimum horizontal stress with depth determine where hydraulic fractures can grow and what orientation of faults will slip. Here, we use a stress model and field data from the Hydraulic Fracture Test Site-1 to simulate hydraulic fracture growth in different landing zones along the length of horizontal wells. We found that strata with lower stress allow for significant lateral growth while strata with higher stress act as barriers to vertical growth. When stimulation occurred in a higher stress zone, the fracture grew both upwards and downwards, whereas in the lower stress zones, fracture propagation was limited by higher stress layers. Although high and low stress layers show characteristic differences in microseismicity, we found no clear relationship between the distribution of microseismic events and the fracture areas. Our results emphasize that the minimum horizontal stress is the primary control on hydraulic fracture growth and must be sufficiently and accurately measured to predict patterns of stimulation.

1. INTRODUCTION

Multi-stage hydraulic fracturing is needed to stimulate production from unconventional petroleum reservoirs due to their extremely low permeability. Hydraulic fractures create new surface area and deliver fluid pressure to pre-existing fractures, causing microearthquakes that increase the area of contact with the rock matrix. Efficient and safe stimulation depends on the ability to control fracture growth and limit stimulation to target intervals.

To propagate through or across any stratigraphic layer, the pressure within a hydraulic fracture must overcome the minimum horizontal stress (Shmin). Since pressure cannot be raised above the value of Shmin where the fracture is generated, layers with higher values of Shmin may act as barriers to hydraulic fracture growth. Shmin also determines the frictional failure criterion for pre-existing faults i.e., what populations of faults are well-oriented for slip and how much fluid pressure is required to induced slip.
Pseudosophronia exustellus (Zeller, 1847) a new species for the Maltese Islands (Lepidoptera: Gelechiidae)
Authors: Seguna A. , Sammut P. , Catania A. , Borg J. J.
Published: October 2022

The genus Pseudosophronia Corley, 2001 and the species Pseudosophronia exustellus (Zeller, 1847) are recorded for the first time from the Maltese Islands. Notes on the distribution and habitat are included.
Time-Dependent Photoluminescence and Photoluminescence Excitation in Exciton Systems and Related Phenomena
Authors: W. Kenney III John , Jacobsen Joshua , Renfro Amanda , Muñoz Isaac , Christian Ruth
Published: October 2022

The term “exciton” covers an extremely diverse range of materials, phenomena, processes, interactions, and experimental techniques. This review provides a general introduction-with selected descriptive examples-of excitonic systems with an emphasis on excitonic photoluminescence and photoexcitation spectroscopy in the ultrafast time-resolved femtosecond time domain.
Electrical Property of Polypropylene Toughened by β Nucleating Agent
Authors: Zhang Ling , Zhou Yuanxiang , Wang Zhaowei
Published: October 2022

High-performance polymer insulating material is a crucial knob for developing HVDC power cables. However, the production process of traditional cross-linked polyethylene, especially degassing, is complicated. The space charge accumulation could render severe electric field distortion under high temperatures and electrical stresses, detrimental to the insulation reliability. As a potential alternative, polypropylene (PP) has excellent properties and is environmentally friendly. However, crucial challenges for the PP application include brittleness deficiency at low temperatures and space charge problems caused by toughened PP composites. In recent years, the β nucleating agent (β-NA) has emerged as an effective additive to improve mechanical and electrical properties due to the introduction of the β-crystal form. Herein, PP/β-NA with different contents and self-assembled β-NA were subsequently prepared, respectively. The melting and crystallization behaviors, crystalline structure, and electrical properties were systematically investigated, and the influence on the space charge characteristics of PP/β-NA composites was explored. We aim to summarize the β-crystal form regulation strategies for advanced PP materials and how they perform, point out the critical characteristic parameters to improve the target performance, and offer suggestions for the rational design for future HVDC cable engineering.
Surgical Management of Scarring Alopecia
Authors: Evin Nuh , Guray Evin Seyda
Published: October 2022

Cicatricial alopecia presents a heterogeneous group of disorders, which are characterized by the destruction of hair follicles, and resulting in scarring and irreversible hair loss. Cicatricial alopecia is classified into two categories depending on the target pathological process. In primary cicatricial alopecia (PCA), the hair follicle is the sole target of a progressive inflammatory process in various skin or systemic diseases. In secondary cicatricial alopecia (SCA), non-specific and generalized disruption of the skin and skin appendages results in fibrotic scarring of the skin and permanent loss of hair follicles due to underlying disease or an external agent. The aim of the treatment of PCA is to reduce inflammation and prevent progression to irreversible alopecia by using immunosuppressive and antimicrobial agents at the earliest phase of the disease. When permanent hair loss occurs in PCA and SCA, scar tissue should be removed or camouflaged by surgical treatment. However, it is difficult to remove the existing scar and treat alopecia. Follicular unit extraction technique hair transplantation is a minimally invasive and alternative treatment with a high success and satisfaction rate in the treatment of cicatricial alopecia.
Current Challenges to World Financial Stability: To What Extent is the Past a Guide for the Future?
Authors: Cukierman Alex
Published: October 2022

The chapter discusses current challenges to world financial stability in light of lessons that have been learned from past financial crises. Although there are parallels between the current situation and some of the previous crises, the current situation differs in several important respects. It comes after a decade of extremely low nominal and real interest rates along with subdued inflation and, due to fiscal and monetary policy measures deployed during the GFC and the COVID-19 pandemic, debt/GDP ratios and central banks (CBs) balance sheets are at historically high levels. The recent upsurge of inflation prompted a worldwide process of increase in policy interest rates and reduction in CB assets. An undesirable side effect of this process is that it may trigger several mechanisms that endanger world financial stability. Recent developments in Fintech and the global economic disruptions caused by the war in Ukraine create novel financial vulnerabilities that differ from previous financial crises. The rapid growth of fintech institutions poses new regulatory challenges at the national and international levels. Although no crisis has materialized to date, those developments have increased the odds of a systemic global crisis. Measures designed to mitigate financial vulnerabilities are briefly discussed in the concluding section.
Allogeneic Transplantation of Hematopoietic Stem Cells (HSCs) for Acute Leukemia in Children – Review of Literature and Experience of Single Center in Russia
Authors: Subbotina Natalia , Dolgopolov Igor , Mentkevich Georgij , Rykov Maxim
Published: October 2022

The indications for hematopoietic stem cell transplantation (HSCT) in pediatric leukemias continually change with the risk-stratification-based treatment improvement. Achieving the minimal residual disease (MRD) negativity before transplantation, using RSI when it’s appropriate, accurate management of post-transplant complications and GVHD are the factors of improving transplantation outcomes. Graft engineering methods are being worldwide investigated also to make HSCT more effective and less toxic, but still there is no gold standard of graft. Use of haploidentical grafts from relatives is a quick and cost-effective option of anti-leukemic efficacy achievement. Upon our experience in Russian Cancer Center, we believe that differentiated diagnosis-based approach to conditioning regimens in haplo-HSCT setting along with maintaining the manageable level of chronic GVHD could provide positive results in pediatric patients with prognostically the most unfavorable leukemias.
A Comparative Study of Students' Academic Optimism and Hope, and Their Relationships with Academic Achievement
Authors: Hayat Ali Asghar , Emad Nafise , Sharafi Negar , Keshavarzi Mohammad Hasan
Published: October 2022

Background: It is critical to identify the factors affecting the academic success of students in the context of medical sciences. The research approaches in positive psychology have shown that the variables of hope and optimism play important roles in the academic achievement of college students. Objectives: The present study aimed to compare and evaluate the relationship between the academic achievement of medical and paramedical students with hope and optimism. Methods: A descriptive-correlative and cross-sectional research design was adopted in this study. The statistical population of the study consisted of all medical and paramedical students at Shiraz University of Medical Sciences. A total of 350 students were selected based on Cochran's sampling formula, out of who 306 ones completed and returned the questionnaires. In order to collect the required data, two valid and reliable scales, including the Adult Hope Scale (AHS) and the Academic Optimism Questionnaire, were used. Moreover, descriptive and inferential statistics were performed to analyze the data by using SPSS 21V software. Results: The findings showed that students’ academic optimism (r = 0.16, P ≤ 0.01) and hope (r = 0.17, P ≤ 0.01) were positively and significantly associated with their academic achievement. The results also indicated that there was a considerable, positive correlation between student identification and their academic achievement (r = 0.197, P ≤ 0.01). Furthermore, a significantly positive relationship was detected between student hope dimensions in terms of agency thinking (r = -0.15, P ≤ 0.05), pathways thinking (r = -0.17, P ≤ 0.01), and academic achievement. The findings demonstrated that paramedical students were significantly more optimistic than medical students (P ≤ 0.01). Conclusions: It was concluded that hope and academic optimism may have increased and improved students’ academic performance and, consequently, had a positive impact on their success and achievement in universities.