bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microscale Observations of Hydraulic Fractures in Gonghe Granite Subjected to Low- and High-Cycle Fatigue Experiments
Authors: Zhuang L. , Zang A. 
Published: September 2022

ABSTRACT:
Previous studies have revealed that hydraulic fracturing behavior in crystalline rock (i.e., granite) is highly dependent on mineral content, grain size, and heterogeneity and is therefore quite different from the behavior observed in sedimentary rock (i.e., sandstone). We investigated hydraulic fracture paths generated via continuous and cyclic injections in Gonghe granite through uniaxial testing. Hydraulic fracturing breakdown pressure was reduced by 20% in cyclic injection. In particularly, we analyzed the role of biotite grains and pre-existing defects - such as natural fractures - in controlling hydraulic fracture propagation. We found that hydraulic fracture crossed natural fracture either without or with an offset in continuous injection, while hydraulic fracture was arrested by natural fracture in cyclic injection, and NF is more likely to be activated during high-cycle injection. This can be beneficial if hydro-shearing of pre-existing flaws is anticipated.

1. INTRODUCTION
The grain-scale heterogeneity of rock has been found to greatly affect crack growth behavior in mechanical fracturing tests. Previous studies have revealed that hydraulic fracturing in crystalline rock for geothermal purposes (i.e., granite) is highly dependent on mineral present, grain size and heterogeneity (Ishida et al., 2000; Zhuang and Zang, 2021). A growing number of work has employed grain-based model coupled with fluid flow in pore network to investigate hydraulic fracturing behavior in crystalline rock, and has reported unique results in terms of asymmetric fracture growth, zipper-mode crack initiation, and the partial re-closure of previous cracks (Kong et al., 2021; 2022), and influence of spatial distribution of minerals (Li et al., 2021). Cracks can be induced in mineral grains (intragranular or transgranular cracking) or along grain interfaces (grain-boundary or intergranular cracks). An in-depth analysis of the hydraulic fracture path can shed some light on the fluid-driven fracture nucleation and fracture propagation process (Chen et al., 2015; Ishida et al., 2016; Zhuang et al., 2020).
Investigating Influence of Freeze-Thaw Cycles on the Degradation of Sandstone Through Discrete Method Modeling
Authors: Huang C. , Zhu C. , Aluthgun Hewage S. , Ma Y. , Shi X. 
Published: September 2022

ABSTRACT:
In this study, the discrete element modeling (DEM) method is adopted to evaluate the influence of freeze-thaw cycles (FTC) action on the mechanical properties of sandstone. A water-rich rock model is built, with rock and water compositions represented by particles of different sizes. To overcome the intrinsic porosity limitation of DEM model and better represent the saturated rock sample, we develop an algorithm to include particles of smaller and varying sizes into rock pores. The ice-water phase change and the resulting accumulation of residual strain are considered by developing a modified elastoplastic model. The rationality of this model is first validated by comparing numerical results with published experimental data. Numerical results highlight the FTC deterioration of the uniaxial compressive strength and Young’s modulus of rock specimens. We establish exponential correlations between the freeze-thaw cycle number and the rock’s mechanical properties such as the uniaxial compressive strength, Young’s modulus and strain energy, showing consistent trends with experimental observations. Inter-particle contact damage also reflects the formation and distribution of micro-fractures in rock specimens under freeze-thaw cyclic treatments. This study provides new insights into the rock degradation process under changing climate and could contribute to the future design and assessment of climate-resilient infrastructure.

1. INTRODUCTION
Rock is a typical porous material that allows water to enter pores and micropores by capillary action in a water-rich environment (Amirkiyaei et al., 2021). When the temperature is below 0 °C, the water in pores is frozen as ice whose volume increases by about 9% (Hou et al., 2021). During the phase change of water, the frost heaving pressure increases due to the constrain of surrounding rock (Wang and Zhou, 2018). The frost heaving pressure produces additional microcracks or enlarges the pre-existing discontinuities of rock, allowing more water to fill into rock after ice thawing and producing more damage under the subsequent freezing. As a result, the physical and mechanical properties of rock are deteriorated after increasing freeze-thaw cycles. Therefore, understanding and predicting rock behaviors after freeze-thaw cycles are critical to prevent the damage of rock-based infrastructures in cold regions and regions that undergo seasonal weather changes.
Mesomechanics-Based Crack Evolution Modeling in Shale Reservoirs Stimulated by Cryogenic Liquid Nitrogen
Authors: Han Songcai , Gao Qi , Yang Junchao , Li Yang , Cheng Yuanfang 
Published: September 2022

ABSTRACT:
A statistical meso-damage thermo-hydro-mechanical (T-H-M-D) coupling model is developed to investigate the trans-scale progressive cracking progress of the shale reservoir stimulated by liquid nitrogen (LN2). The theoretical framework encompasses: (1) local thermal equilibrium theory to formulate the heat exchange between the rock matrix and the cold fluid; (2) compressible fluid seepage theory to simulate the mass transport in pore media; (3) classical thermo-poroelatic theory to analyze the matrix deformation characteristics; (4) elastic-brittle-damage theory with double damage functions to identify the shale failure process at low temperatures; (5) two independent statistical distribution functions to describe the shale meso-scale heterogeneity in both thermos-mechanical and hydraulic properties; (6) Helmholtz free energy functions to calculate temperature- and pressure-dependent fluid thermodynamic properties; (7) experimental and empirical formulas to characterize temperature- and damage-related rock properties. The numerical model is implemented into the finite element method to analyze the underlying response mechanisms of the shale reservoir interacting with LN2. Simulation results show that LN2-shale interaction can induce multiple initiation positions, resulting in multiple asymmetric macro-cracks. The failure mechanism of the shale during cryogenic fracturing is dominated by elastic-brittle tensile-induced damage. Cryogenic shock to enhance shale elastic modulus and induce thermal tensile stress is beneficial to forming complex fracture networks. It is also found both fracture initiation pressure and induced fracture morphology are more sensitive to fluid injection temperature relative to reservoir temperature.

1. INTRODUCTION
At present, large-scale hydraulic fracturing is widely used in shale gas reservoirs to generate complex fracture networks. However, microseismic monitoring results have shown that some gas-rich shale layers with high temperature, high stress, low brittleness, and undeveloped natural fractures, cannot create a sufficient stimulated reservoir volume (SRV) when adopting conventional hydraulic fracturing (Zou et al. 2015; Lei et al. 2021). Additionally, the use of water-based fracturing fluid will bring about many serious problems such as formation secondary damage, fluid backflow difficulty, and water resource waste etc. (Middleton et al. 2015; Kalam et al, 2021).
Mechanism Study of a Novel Expandable Deep-Water Drilling Conductor on Improving the Bearing Capacity of Subsea Wellhead
Authors: Zhang Minghe , Yang Jin , Wang Yuanming , Li Lei , Zhou Yisu , Yang Yuxiang , Xu Dongsheng , Zhu Guojing 
Published: September 2022

ABSTRACT:
A novel expandable drilling conductor is designed to enhance the bearing capacity and stability of subsea oil and gas wellheads in deep-water. The basic structure is the annular expandable materials installed on the surface of the conductor, which changes the interaction between cylinder foundation and surrounding soil, and the annular expandable materials are connected with the conductor to form a similar variable section rack structure, which increases the occlusive effect between the conductor and the stratum. This study proposes the method of combining theoretical models with laboratory experiment and field test for analysis. A new model of expandable conductor and soil strata is presented. Results show that the novel expandable conductor can significantly increase the vertical bearing capacity of the foundation, the end of the annular material area (the thickness of the material), the length of the annular material, and the distance of ring material are the main factors affecting the vertical flexural bearing capacity, and the distance and the thickness of the material and the shear strength of soil are closely related. This kind of variable section pipe can be used as a new type of pile foundation structure to effectively increase the stability of the foundation.

1. INTRODUCTION
Structural casing jetting operations have become commonplace in deep-water environments. Having originated in the Gulf of Mexico (GOM), the structural casing is now jetted in most deep-water basins in the world (Akers, 2008). Very little literature has been published regarding jetting practices. The lack of published literature, combined with the complex mechanics and hydraulics of the process and the lack of detailed soil data at most locations, results in an operation that is heavily dependent on the experience and expertise of the rig-site team.
The deep-water drilling conductor is an important bearing device, and the bearing capacity generated between conductor and soil is used to carry the wet weight of wellhead, mud mat, cam-actuated drill-ahead (CADA), etc. There are usually three methods of conductor installation: jetting, drilling, and hammering (Yang et al., 2010; Pereira, M. F. et al., 2013; Roy et al., 2018). In recent years, the conductor anchor node (CAN) has been developed and successfully applied as an emerging technology (Sivertsen et al., 2011; Kan et al., 2018). In contrast, the jetting method is most mature and has been widely used in the Gulf of Mexico (GOM), West Africa, Southeast Asia, and South China Sea (Jeanjean, 2002; Mackenzie et al., 2012; Prasertamporn, 2016; Wei et al.,2019). In this paper, we focus on the jetting method.
Integrated Assessment of Interaction Between Supercritical CO2 and Shale During Thermal Maturation
Authors: Onwumelu C. , Kolawole O. , Bouchakour I. , Ozotta O. 
Published: September 2022

ABSTRACT:
Recent studies have shown that shale reservoirs can be an attractive candidate as a CO2 storage reservoir or a caprock for geologic CO2 sequestration. Shales are source rocks, and thus, there is a continuous diagenetic process that can alter its properties during thermal maturity before it reaches maturity. However, there is a significant knowledge gap in the geochemical and other alterations in shales due to the interaction with supercritical CO2 (ScCO2) stored in the underlying reservoir unit during the diagenetic process. This study investigates the changes in mineralogical properties and Total Organic Carbon (TOC) of shales during thermal maturation when it is exposed to ScCO2 at in-situ conditions and assesses its implications for CO2 utilization and sequestration. Here, we used Bakken shale and Green River shale samples, and exposed the samples to ScCO2 for a specific period. This was followed by inducing the samples to thermal maturity for the pyrolysis process. Subsequently, we evaluated the mineralogical properties and TOC of the pre- and post-CO2 treatment of mature shale samples. Our results from this study provide novel insights for CO2 utilization and sequestration in the mature Bakken and Green River shale formations.

1. INTRODUCTION
Carbon dioxide is injected into the subsurface in a supercritical phase. Supercritical CO2 (ScCO2) state is found above the critical point of temperature and pressure of 31.8 C and 7.38 MPa, respectively where CO2 behaves like a gas but with a density like that of a liquid (Span and Wagner, 1996). There are three recognized geological formations for CO2 storage: saline aquifers, depleted oil and gas fields, and coalbeds. Basically, injection of CO2 has two economic benefits (Baines and Worden, 2004): first, a financial incentive with the carbon tax credits by solely capturing and storing CO2 (e.g., saline aquifers) to reduce CO2 emissions in the atmosphere. Secondly, utilization of CO2 injection in enhanced oil recovery (EOR) or coalbed methane production. Once the CO2 percolates the reservoir, it migrates upward due to buoyancy reaching the top of the formation where it is contained by a cap-rock layer. Trapping mechanisms play a key role in preventing leakage risk (Fatah et al., 2020) and are not only structural and stratigraphic, but also related to the trio CO2-fluid-rock interactions. In residual or capillary trapping, CO2 droplets are immobile and trapped in pore space (Kang, 2011). Solubility trapping happens when CO2 dissolves in brine water or is trapped by mineral precipitation.
A New Approach for Mitigating Subsidence Influences on High Tower Structures Induced by Longwall Mining Based on Foundation Grouting Reinforcement Mechanism
Authors: Zhao Gaobo , Guo Wenbing 
Published: September 2022

ABSTRACT:
This paper presents a new approach for mitigating high tower structures slope based on the foundation grouting reinforcement (FGR) mechanism. Three effects of the FGR approach were analyzed: the reinforcement provided by grouting to improve the strength of the foundation, filling gaps around foundation provided by grouting materials to compensate for the subsidence, and adjusting foundation elevation provided by controlling grouting pressure to reduce the slope of the high tower structure body. The FGR mechanism was further developed by the theoretical analysis of foundation vertical deformation under the effect of grouting, and the theoretical equation for calculating the grouting pressure based on the subsidence induced by longwall mining was derived. Finally, the systematic procedure of the FGR approach was presented, and applied to mitigate the slope of a radio signal tower located above the active panel of a Chinese coal mine. The results of this application show that: after implementing the FGR approach, the tower foundation slope decreases as face advances, and is less than its limited deformation.

1. INTRODUCTION
High tower structures refer to structures with large height and relatively small cross section. Taking horizontal load (especially wind load) as the main basis for structural design (Shu et al. 2018), they can be divided into self-supporting tower structure, guyed mast structure, and lattice steel tower structure (Lee and McClure 2007), mainly including high-voltage transmission tower, radio signal tower, and communication tower, as shown in Fig.1. Particularly, in China, there are abundant recoverable coal reserves buried under high-voltage transmission lines in coal mines(Guo and Yong 2011). For examples, in Yanzhou Coal Mine, 21.89 million tons of recoverable coal reserves is under high-voltage transmission lines; the first 1000 kV high-voltage transmission line passes through Sihe Coal Mine, affecting a total coal reserves of 30.78 million tons. It is a technical and engineering problem to mining these coal reserves without affecting the high-voltage transmission lines safety.
Analysis and Modeling of Explosive Fracturing Process in a Transparent Surrogate of Jointed Rock
Authors: Vorobiev O. Yu. , Robey R. E. , Pope J. , Torres S. M. , Hargather M. J. 
Published: September 2022

ABSTRACT:
The paper describes analysis and modeling of dynamic experiments with 1-foot-size blocks of a transparent rock substitute, PMMA. During these experiments, 0.3-0.7 grams of explosive was detonated in the middle of a multilayered cubic block in single and double tamped wells. Numerical modeling in combination with the analysis of experimental records helps to understand the mechanism of dynamic fracture and to predict the fracture process for a nontransparent granite block with and without preexisting fractures which will be used at the next stage of this study.

1 INTRODUCTION
In traditional hydraulic fracturing stimulation, the effective conductivity of low permeability rock is increased by generating or activating fractures through injection of pressurized fluid. Methods that use dynamic loading from explosives and propellants potentially extend stimulation to previously unrealized geological resources. In contrast to traditional fracturing methods (e.g. hydraulic fracturing) the stresses in the source region may be significantly larger than the in-situ stress, which helps to create fractures not oriented with the maximum in-situ stress. Fractures initially are generated by the diverging stress wave propagating from the energy release zone. It has been shown in the past that the crack area and final extend depend on the ability of explosive products to flow into the cracks after the wave propagation, e.g., Kutter and Fairhurst (1971); Nilson (1981). The gas flow fracture mechanism has been confirmed in the current work utilizing high - speed schlieren imaging, and Photon Doppler Velocimety (PDV) during recent explosive fracturing experiments with 0.3-0.7 g of high explosive source detonated in prestressed 1-foot PMMA cubic blocks with and without artificial joints (Hamm et al. (2021)). Modeling of these experiments presents a significant computational challenge, as various physical scales need to be resolved to address this problem. Thus two major temporal scales to be resolved are the shock wave propagation scale related to the time required for the shock wave to propagate across the sample and the time required for the explosive products to escape into the cracks generated around the cavity by the outgoing shock wave.
Special Triaxial Experiments on the Fracture Behavior of Hollow Rock Salt Specimens
Authors: Baumgärtel L. , Körner F. , Leuger B. 
Published: September 2022

ABSTRACT:
The knowledge of possible fracture formation and propagation in rock salt caverns is an important aspect for their safety-oriented design. During gas withdrawal the internal pressure is reduced and the associated cooling of the gas and thus also of the cavern wall cause a reduction of the principal stresses and can possibly lead to finite fractures at the cavern wall, if the minimal stress component falls below the present gas pressure by a certain stress difference.
The described induced thermal stress reduction is subject of investigations in laboratory tests on hollow cylinders of natural rock salt. For this purpose, the specimen is loaded with a quasi-hydrostatic pressure (axial, circumferential and internal gas pressure) and unloaded in a pressure-controlled manner by reducing axial pressure (corresponding vertical rock pressure) at constant gas pressure in order to mechanically reproduce the expected result of thermal cooling. The unloading of the hollow cylinder by one stress component shows a so-called infiltration fracture at mechanically absolute compressive stresses in all three main stress directions due to the existing constant inner pressure and the mechanical loading situation.
Four specific laboratory tests and their impact on the rock mechanical design of a gas storage cavern are discussed and compared in this paper. The measured stress differences are investigated with respect to the influences of test and specimen parameters under stress conditions during gas withdrawal in rock salt caverns. Ultrasonic measurements provide a first basis for estimating possible stress differences for these four tests. The initial pressure as well as the selected pressure reduction rates do not correlate with the level of the stress difference.

1 INTRODUCTION
The consumption of natural gas in Germany in 2020 was 86.50 billions m3, which represented 25.74 % of primary energy consumption (BP, 2021). Rock salt caverns are suitable for storing energy sources such as natural gas or mineral oil. At the end of 2020, the working natural gas volume, which could be stored in underground caverns in Germany, totaled 15.19 billions m3 (Vn, Conditions: 273.15 K, 1.01325 bar) (EID, 2021) respectively 17.50 % of the natural gas consumption without requiring large areas above ground. Energy storage caverns thus have the potential to store and hold large amounts of primary energy efficiently.
Using 3D Printing to Improve Fracture Conductivity Experiments
Authors: Obi C. E. 
Published: September 2022

ABSTRACT:
Using 3D printing technology, fracture conductivity test samples are replicated to overcome the challenge of sample inconsistency. The fracture surface topography data is acquired with three different techniques. A laser profilometer, Computed Tomography (CT) scans, and photogrammetry. The developed and printed 3D models are used to make Fracture conductivity test sample replicates of cement/shale and cement/sand mixtures. We validate the replicability of these samples based on visualized scans of the fracture surface of the original rock samples, 3D molds, and concrete replicates. We also used the joint roughness coefficient (JRC) to quantify and validate the replicability of these samples. The Meremac and Austin chalk formations are the source of the original Fracture conductivity samples used. The replicability ranged from 78% to 99% for the Meremac core using CT scans and Digital Light Processing (DLP) printer. The replicability range was from 75% to 93% for the Austin chalk core using the photogrammetry technique and Fused Deposition Modeling (FDM) printer. The final check for replicability and validation of methodology used is with the fracture conductivity results. The cement/sand mixture replicates C5 and C7 that cured for relatively similar conditions produced similar fracture conductivity results. The cement/sand mixture replicates C5 and C7 which were cured for relatively similar conditions produced very similar fracture conductivity results. We also observed that the mechanical properties and surface topography of rock samples dominate fracture conductivity behavior significantly at closure stress within the peak strength of the rock sample. This study provides a methodology for achieving consistency of fracture conductivity test samples.

1. INTRODUCTION
3D printing has gained traction in recent years as a very applicable technology to many fields such as biological medicine, education, aviation, engineering, and most recently rock mechanics. The true investigation of the mechanical and related behavior of rock samples by conventional methods over the years has been limited by the replicability of these tests which is mainly due to significant heterogeneity (Jiang et al. 2016).