bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACT:
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

ABSTRACT
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

ABSTRACT:
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

ABSTRACT:
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

ABSTRACT:
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

ABSTRACT:
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

ABSTRACT:
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

ABSTRACT:
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.
L’aide médicale à mourir pour les personnes atteintes d’un trouble neurocognitif majeur : analyse des commentaires de participants à une enquête
Authors: Bravo Gina , Arcand Marcel , Trottier Lise 
Published: October 2022

Nous avons récemment réalisé une enquête postale panquébécoise pour connaître les attitudes de divers groupes face à l’idée d’étendre l’aide médicale à mourir (AMM) à des personnes en situation d’inaptitude. Nous présentons ici les résultats d’analyses qualitatives des commentaires laissés par les répondants à la fin du questionnaire. Celui-ci avait été posté à quatre groupes cibles : des aînés de 65 ans ou plus (n=621), des proches aidants de personnes atteintes d’un trouble neurocognitif majeur (n=471), des infirmières (n=514) et des médecins (n=653) qui prenaient soin de tels patients au moment de l’enquête. Des 1 050 questionnaires retournés, 420 incluent des commentaires. Ces commentaires ont été codés en rubriques, thèmes et sous-thèmes, et la fréquence des rubriques comparée entre les quatre groupes cibles. Le codage a permis d’identifier 23 thèmes et cinq sous-thèmes que nous avons regroupés en sept rubriques principales : 1) le répondant, 2) l’enquête et son questionnaire, 3) les personnes visées par l’extension, 4) leur proches, 5) le système de santé, 6) le cadre législatif qui balise les soins en fin de vie, et 7) la société en général. Ces rubriques ont été repérées dans les quatre groupes cibles, bien qu’à des fréquences différentes pour cinq d’entre elles. La présente étude met ainsi en lumière une panoplie de facteurs susceptibles d’influencer les attitudes face à l’extension de l’AMM aux personnes inaptes. Elle illustre par ailleurs la valeur ajoutée de soumettre des commentaires à une analyse systématique pour mieux comprendre les résultats d’une enquête postale.