bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Investigation of Particle Bridging near Fracture Entrance
Authors: Han Yanhui , Luo Bo , Chang Frank , Li Wenwen 
Published: October 2022

ABSTRACT:
Particle transport and bridging inside fractures is an important subject in wellbore drilling and completion. For example, when drilling naturally fractured formations, depleted formations, and offshore formations where fractures can be easily induced or reactivated, loss circulation material (LCM) containing high loading of solid particles is commonly used to seal the pre-existing or newly created fractures to prevent mud loss. The particles are expected to bridge the fracture at the entrance area to maximize the sealing effectiveness and efficiency. A different example is the well completion with hydraulic fracturing, in which the proppant particles are injected with fracturing fluids to keep the fractures open after the fracturing pressure is released. To maximize the opening area of the fractures thus the well productivity, the placement of the proppant particles is expected to reach the far region of the fractures, so the particle bridging near the fracture entrance should be avoided. On the other hand, should the objective be promoting multiple fractures, particle bridging against a pre-existing or dominant fracture is beneficial to redirect the fracturing fluid into less conductive fractures. The ability to predict the bridging location and time with given solid particle size and concentration, fluid viscosity and operating parameters will help design drilling fluid, LCM, fracturing fluid, and diverting materials. In this work, a simulator is developed for numerically experimenting the particle bridging in the entrance area of a fracture. The fluid flow in the fracture is simulated by pipe network flow model. The equation of particle advection with fluid is solved using the upwind numerical scheme. The particle bridging is evaluated using a blocking criterion proposed in the literature. After all the implemented computational components are tested and verified, extensive parametric studies are then performed to experiment how various parameters, including particle size and concentration, fluid viscosity and injection rate, influence the particle bridging location and time near the entrance area. Accordingly, a few recommendations are provided to assist the design and selection of diverting and LCM agents.
Laboratory Characterization of a Synthetic Sandstone for Tunnel Rockburst Study
Authors: Wibisono D. Y. , Arora K. , Gutierrez M. 
Published: October 2022

ABSTRACT:
Assessment of rockburst potential in the rockmass is one of the main challenges in tunnel design. The phenomenon of rockburst is often linked with brittle failure characteristics of the rock leading to high strain-energy release and spalling, fractures, and damage around the tunnel boundary. This paper develops a synthetic sandstone as a model material for bursting rocks prepared in the laboratory to advance the study of the rockburst phenomenon. The synthetic sandstone is composed of fine-grained F-75 Ottawa sand, type I/II cement, and water. The brittle behavior of the material was studied based on the full stress-strain curve observed in the synthetic sandstone. Also, the synthetic rockburst-susceptible rock suitability is evaluated using several empirical criteria, such as strength brittleness index, burst energy coefficients, a brittleness index modified, and a strain energy storage index. The laboratory tests found that the material can be easily reproduced in different shapes and geometry with repeatable properties. The elemental testing damage characterization of the synthetic sandstone shows that the material is similar to bursting rock. The synthetic sandstone will be further expanded in laboratory-scale physical model testing using a true-triaxial cell to study the complex problem of rockburst.

1. INTRODUCTION
The sudden, violent manner of rockburst is a complex phenomenon that remains a significant hazard for many deep underground excavations (Simser, 2019). Understanding the primary cause of rockburst and its interdependence enables engineers to make more informed risk management and mitigation decisions. One approach to improve the understanding of the failure process for the excavation is building a reproducible physical model under controlled circumstances in different shapes and geometry (Klammer et al., 2017).
Although categorized as medium strength rocks, historical evidence has shown that rockburst can occur in this lithology (Q. M. Gong et al., 2012; Naji et al., 2019; Sun et al., 2016). Researchers have attempted to produce artificial rocks similar to natural sandstone in the past few decades. The efforts include a sintering process of natural sand grains with artificial beads, artificial cement, 3D printing, and chemical reaction utilization (David et al., 1998; Huang and Airey, 1998; Ishutov et al., 2015; Osinga et al., 2015; Rice-Birchall et al., 2021). However, these methods necessitated extensive resources and were considered limited in terms of ease of preparation.
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

ABSTRACT:
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

ABSTRACT:
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

ABSTRACT:
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

ABSTRACT:
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

ABSTRACT:
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

ABSTRACT:
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

ABSTRACT:
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).