bluuebunny/crossref_metadata_2025_split huggingface dataset:
A New Analysis Method for the Influencing Factors of Surrounding Rock Stability and its Application
Authors: Li Peitao , Liu Quansheng 
Published: September 2022

ABSTRACT:
A new orthogonal matrix analysis method is proposed firstly in this paper, which aims at providing a new idea for the stability analysis of surrounding rock. Based on the orthogonal test method, a three-level analysis model is established. In detail, the geological conditions and rock masses grade, the variation of different factors, the deformation and fracture field of surrounding rock is regarded as the factor layer, the level layer, and the index layer, respectively. This method not only inherits the advantages of orthogonal test, but also avoids the influence of artificial weighting by establishing the index layer. Then, based on the combined finite-discrete element method, the influence of lateral pressure ratio, vertical stress, and rock mass grade on the surrounding rock stability is carried out by three analysis methods. The results show that the orthogonal matrix analysis method can well reflect the influence of factors, which is consistent with the result of the range analysis method and variance analysis method. In addition, this method can also realize the quantitative sensitivity analysis of factors under different levels, which is essential for the surrounding rock support design.

1. INTRODUCTION
As we all know, the stability of roadways is affected by many factors. So, the research on the stability of surrounding rock is still a challenge. It has an important reference value for roadway excavation and support. Currently, many experts and scholars have proposed different methods and models to evaluate the stability of surrounding rocks. These include experimental methods (Chen et al., 2021), numerical simulation (Jia et al., 2022), theoretical analysis (Zhang et al., 2022), etc.
The laboratory experiment is the basic method that evaluates the stability of surrounding rock based on the test result of rock samples. The numerical simulation is the most common method, which includes continuum mechanics methods (Tian et al., 2021; Wang et al., 2022), discontinuous mechanics methods (Lisjak and Grasselli, 2014; Zhao et al., 2022), continuum and discontinuous combination method (Deng et al., 2020; Mahabadi et al., 2012). The theoretical analysis method is based on the analysis of the stress field and deformation field, which contains the longitudinal deformation profile (Sugimoto et al., 2019), ground reaction curves (Fang et al., 2013), the pressure arch (Kong et al., 2018) and the stand-up time (Nguyen and Nguyen, 2015).
Optimization Design Method of Excitation Parameters and Installation Parameters of Downhole Vibration Drag-Reduction Tools
Authors: Shi Xiaolei , Huang Wenjun , Gao Deli , Ye Yuchen 
Published: September 2022

ABSTRACT:
In the sliding steerable drilling operation in long horizontal wells, vibration drag-reduction tools can greatly reduce tubular drag, effectively alleviate frequent pipe sticking problem and improve rate of penetration. The excitation parameters and installation parameters of vibration drag-reduction tools are closely related to the drag reduction efficiency. At present, the parameter design of vibration drag reduction is mainly based on field experience but lacks a set of effective theoretical methods. To solve this problem, the strong nonlinear effect of friction force is considered, the dynamic model of drill string with vibration drag-reduction tools is built and the drag reduction laws under different parameters are revealed. On the basis of vibration propagation distance model and inverse torque action distance model, an optimization design method of excitation parameters and installation parameters of vibration drag-reduction tools is established with drag reduction efficiency as the objective function and drill string fatigue failure and hydraulic energy loss as constraint conditions. Finally, the above theoretical model is applied to practice. The results show that the amplitude of the excitation force, the number and installation position of the drag-reduction tools are the main factors affecting drag reduction efficiency. With the increase of excitation force amplitude and the number of drag-reduction tools, the drag reduction efficiency increases continuously., the drag reduction efficiency when the vibration propagation ranges of multiple tools are independent is higher than that when not independent. There is a risk of tubular fatigue failure if the amplitude of the oscillator excitation force is too large, and a risk of too high hydraulic energy loss if too many drag-reduction tools are installed. In the case study, it is recommended to use three vibration drag-reduction tools with excitation force amplitude of 50kN, which are installed at 435m, 1038m and 1641m away from the drill bit respectively, and then a drag reduction efficiency of 54% is achieved.
Exploring the Geometry of Fracture Intersections Under Stress
Authors: Santos A. M. , Hu M. , Pyrak-Nolte L. J. 
Published: September 2022

ABSTRACT:
The behavior of intersections is central to the fluid flow and transport evolution of a fracture network in response to chemical and physical processes. Here, laboratory experiments were performed to explore the evolution of network geometry during loading of a 3D printed fracture network composed of two intersecting orthogonal fractures. 3D X-ray microscopy was used to image the changes in the fractures and intersection for two orientations of the network, "+" and "X", relative to an applied normal load. For the "+" orientation, the connectivity along the intersection was maintained by the vertical fracture that did not deform significantly under load. However, when the network was rotated to the "X" orientation, the void volume decreased along both fracture planes and the connectivity between the two orthogonal fractures ceased to exist at the highest load. The orientation of fracture networks relative to a local stress field affects the flow paths in the individual fracture planes and the connectivity of the fracture network.

1. INTRODUCTION
Fracture networks in rock provide the connected flow paths through which fluids are injected or withdrawn from subsurface reservoirs during energy production (e.g. geothermal, oil & gas, H2 storage) and anthropogenic waste isolation (e.g. CO2 sequestration, nuclear waste). While the mechanical and hydraulic behavior of single fractures are well understood (e.g. Pyrak-Nolte & Nolte, 2016), less laboratory research has focused on fractures networks (e.g. Hull, 1986; Montemagno & Pyrak-Nolte, 1999; Johnson & Brown, 2001; Johnson et al., 2006) and how they deform under stress (e.g. Frash et al., 2016, 2017 & 2019). Transitioning from an individual fracture to a 3D fracture network increases the complexity of a fracture system by introducing fracture intersections. Though intersections compose only a tiny fraction of the total void volume of a fracture network, closure or opening of an intersection can radically affect the transport paths and connectivity of a network.
Our view of fracture networks is often based on 2D views from outcrops (Figure 1) or boreholes. Although fracture networks are intrinsically 3D, the 2D sections enable one to infer the topological elements of the system (Bai & Pollard, 2000; Sanderson & Nixon, 2015; Peacock et al., 2018; Laubach et al., 2019). One of the simplest topological elements of a fracture network is shown in Figure 1c and is referred to here as "X". This topological element is composed of 2 intersecting fractures with 1 intersection (Figure 1c).
Estimating Rock Mass Joint Roughness Using Terrestrial Laser Scanner and Artificial Neural Network
Authors: Lee S. , Jeon S. 
Published: September 2022

ABSTRACT:
Joint roughness is one of the most important factors which decide the shear behavior of a rock mass. Conventionally, it is quantified into a parameter called Joint Roughness Coefficient (JRC) by visual comparison between Barton’s standard profiles and line profiles of a joint. Since the line profiles are acquired by hand-mapping using a roughness profiler, it is hard to survey unreachable parts of the rock mass. In this regard, we suggest a method to estimate the roughness of discontinuities using a Terrestrial Laser Scanner (TLS) which enables contactless data acquisition from long range. To resolve problems that TLS point clouds are unordered and containing noise, we used an artificial neural network called PointASNL. We generated synthetic surfaces that resemble joint surfaces scanned by TLS to fill the need of big data for training a model. After training, the model was evaluated with the result of roughness estimation for an outcrop scanned by a TLS device. It is shown that the model can estimate the roughness with average error of JRC 3-4.

1. INTRODUCTION
Terrestrial Laser Scanner (TLS) is a device which scans surrounding surfaces quickly and translates them into a massive 3D point cloud. Laser emitted from the laser diode goes through the rotating mirror at the center of the device to head towards the surfaces and comes back after reflection. Rangefinder and gimbal inside measure the travel time of the laser, vertical angle between horizon and a point, and the horizontal direction to calculate 3D coordinates of the surfaces. Most TLSs can be operated in a distance of several to hundreds of meters and the rapid rotating mirror enables to get millions of data points in less than tens of minutes. Therefore, one can easily reconstruct the surrounding area or objects into a 3D point cloud for various purposes (e.g. 3D map construction, quality inspection for huge parts).
Analysis of Elastic Properties of Organic Rich Shale Based on Petrophysical Model
Authors: Wang Xiaoqiong , Sun Yueyue , Zhang Qian , Ge Hongkui 
Published: September 2022

ABSTRACT:
In this paper, Longmaxi formation shale in Fuling area is taken as the research object. The elastic wave velocity test is carried out to evaluate the elastic properties, and the relationship between the mineral compositions of the rock and the elastic wave anisotropy of is discussed. The experimental results show that the clay kerogen combination distributed in the inorganic mineral background is the main controlling factor of the anisotropy of the target reservoir. Therefore, using the anisotropic differential equivalent medium model (DEM), the clay kerogen combination is established. Then the combination is added into the inorganic mineral matrix as the adding phase, and the inorganic pores and organic pores are added in order to characterize the anisotropy of the target reservoir to the greatest extent. The error between the final model calculation results and the measured wave velocities in the laboratory is within 10%. The model has high reliability and can better reflect the elastic properties of the target reservoir. Finally, the model is used to further simulate and analyze the effects of microcracks content and aspect ratio, kerogen content and maturity on the elastic properties of rocks.

1. INTRODUCTION
With the successful exploitation of shale gas in North America, the exploration and exploitation of shale gas has become a new strategic target of oil and gas resources development. China is rich in shale gas resources. Taking Changning, Weiyuan, Fuling and Zhaotong areas in South of China as examples, marine shale gas has initially achieved large-scale benefit development. Unlike conventional reservoirs, shale reservoirs generally have the characteristics of low porosity and low permeability, with complex pore structure, most of the connected pores are micro-nano pores (Loucks et al., 2009; Sondergeld et al., 2010). The elasticity of shale formed in different sedimentary environments is obviously different. The research on the physical characteristics of shale reservoir has important guiding significance for the identification of geological sweet spot and engineering sweet spot.
The Hidden Value of Insufficiently Preserved Shale Material
Authors: Stroisz A. M. , Bhuiyan M. H. , Agofack N. , Edvardsen L. , Cerasi P. 
Published: September 2022

ABSTRACT:
The research is focused on investigating if insufficiently preserved shale can still be valuable in a correct geomechanical characterization of the material. This is achieved by targeted attempts leading to reverse the processes that diminished the quality of the material in the first place, allowing the shale to regain the original rock properties. The focus is limited, for now, to recapture the saturation state by investigating the fluid effect on the mechanical and acoustic response. A considerable number of basic mechanical and acoustic tests were conducted on poorly preserved Opalinus clay to identify the pristine properties of this material. Among these, the strength of the shale was measured by unconfined compressive strength, scratch, and punch tests, whereas the acoustic wave velocity was tested by continuous-wave technique and through-transmission method. The experiments were performed for three saturation states: ‘as-received’, dry and re-saturated. To confront the outcome, the same test campaign was conducted on well-preserved Opalinus clay from a nearby location, at the Mont Terri underground laboratory in Switzerland. Results show that obtaining valuable data on the damaged cores, such as unpreserved shale, is possible by utilizing adequate testing methods. One example are tests on the small-size samples that provide reliable information regarding the acoustic and mechanical properties of the material. It is, however, disputable to what extent one can recover the original properties from the unpreserved material.

1. INTRODUCTION
Shales make up more than 70% of drilled formations. Therefore, understanding shale properties is crucial for many subsurface activities. These include operations such as gas storage (carbon dioxide or hydrogen), well-integrity, borehole stability prediction, evaluation of shale as a permanent barrier, as well as infill drilling and mining activities. Characterization of the shale can be carried out by both direct and indirect methods. The first relies on conventional core analysis, whereas the others are based on petrological models of log data. Although the direct methods are seemingly more reliable, they require access to material with sufficient quality and being well-preserved. The shale core extraction is, however, a very costly and demanding process. Therefore, finding the way to obtain data from (i) insufficiently preserved cores, e.g., dried out due to inadequate sealing, (ii) post-tested samples and remnants, or even (iii) cuttings collected on well-site, is of great interest to the industry. Input from the petroleum industry and literature search gives the impression of a clear knowledge gap on understanding the effect that insufficient preservation has on the results and how to achieve fast, inexpensive, and reliable geochemical, mineralogical, petrophysical, or mechanical data from poor-quality material.
Direct Measurements of Intra-Fracture Hydraulic Heterogeneity on a Multi-Meter Scale
Authors: Libby S. , Hartley L. 
Published: September 2022

ABSTRACT:
The Olkiluoto site is a proposed spent nuclear fuel disposal facility in Finland. Surface-based drilling and logging of more than fifty drillholes has provided the basis for characterizing bedrock fracture models and associated hydraulics at the site. Alongside core and image logs, the high resolution Posiva Flow Logging (PFL) tool allowed the interpretation of fracture-specific flow statistics and their correlation with structural properties, orientation and geological domain. This permitted characterization of inter-fracture variability. However, because of the hundreds of meters between investigation holes it was not possible to conceptualize heterogeneity within single fractures. A new underground dataset has become available from the excavation of four c. 400 m deep vertical access and ventilation shafts, where dense drilling around the circumference of the shafts for several wet sections has been performed as part of pre-grouting operations. PFL testing in these holes and the subsequent grout injection data provided an opportunity to characterize both multi-meter scale in-plane heterogeneity and flow dimension, and thereby better understand flow channeling and water-rock interactions.

1. INTRODUCTION
Nuclear power offers a reliable and low carbon source of energy, however, the safe disposal of the spent fuel is a significant associated challenge. The primary option for achieving safe disposal is the emplacement of spent fuel in tunnel systems hundreds of meters underground. Several countries are building or evaluating repositories in high strength and low permeability rocks such as the high-grade metamorphic rocks at Olkiluoto. However, bedrock fractures (or joints) form planes of weakness and potential conduits for fluid flow. Consequently, understanding the fracture systems and the flow of fluids within them is a prerequisite for assuring both construction/operational safety and long-term resilience of waste containment.
At the Olkiluoto spent nuclear fuel disposal facility in Finland, four shafts have been excavated to circa (c.) 430 m depth. The four shafts have individual roles, permitting access for spent fuel, air inflow, air outflow and personnel, and are labelled accordingly in Fig. 1. Prior to the excavation of the shafts, hundreds of holes were drilled inside or outside each shaft for pre-grouting purposes. They are concentrated in relatively wet sections, such as near the surface and where the shafts pass a major sub-horizontal fault. Most of these holes were surveyed with the Posiva Flow Logging (PFL) tool (described in Section 2), which provided an exceptionally dense distribution of transmissivity data measurements. In combination, this dense three-dimensional distribution of data points and sparse fracturing allows subsets of the data points to be attributed to single fracture planes. This provides a rare opportunity to observe and quantify heterogeneities in the flow properties of single fractures on the multi-meter scale.
Pore Boundary Deformation and the Biot Coefficient: A Micromechanical Analysis
Authors: Müller T. M. , Couples G. D. , Sahay P. N. , Basabe J. D. 
Published: September 2022

ABSTRACT:
Continuum poroelasticity theories provide a macroscopic description of fluid-saturated porous media so that pore-scale features only emerge in some averaged form. However, therein the specific signature of the underpinning micro-structure is not transparent in the constitutive material equations. For a regular lattice-type micromechanical model, we derive an exact formula for the Biot coefficient. As anticipated by experimental and numerical studies, the Biot coefficient embodies a nonlinear combination of the elasticity of the solid phase material and the geometry characterizing the pore space. This result allows us to exemplify the abstract concept of pore boundary deformation appearing in the continuum description of porous media including the ramifications of a geometrical self-similar deformation. Although this is certainly an oversimplified model for most porous rocks, our analysis may serve as benchmark for numerical upscaling based on digitized images to infer the poroelastic material parameters and thus to support ongoing experimental efforts to measure poroelasticity coefficients.

1 INTRODUCTION
Whenever a porous medium is elastically deformed, the internal pore boundaries experience deformation, resulting in a pore space volume change. Though its absolute value is on the order of the elastic strain, this pore space volume change is one of the most fundamental characteristics of deformable porous media, and yet, its direct measurement is difficult to achieve. Typically, it is indirectly measured through the amount of fluid that is squeezed out of the porous matrix upon compression. Such measurements are notoriously difficult to master and this is one reason why measurement results of poroelastic constants are error-prone and, more often than not, lead to misinter-pretation (e.g., Nowakowski, 2021).
The pore boundary deformation also causes a nonlinear correlation between porosity and the Biot coefficient, which to a limited extent can be modeled by taking into account the shape and arrangement of pore-scale heterogeneities in an effective medium theory (e.g., Selvadurai 2020) or more advanced computational approaches (Dehghani and Zilian, 2020).
The Inversion of Mechanical Parameters of Weak Surrounding Rock in High-Stress Tunnel After Casting Anchor
Authors: Jiang Y. , Zhou M. L. , Ning L. , Jiang H. H. , Yao Y. 
Published: September 2022

ABSTRACT:
This study investigates the performance of yielding bolt in a weak rock mass tunnel with high in-situ stress conditions. The genetic algorithm and the Komamura-Huang rheological model are combined to perform an inversion analysis of the mechanical parameters of the weak surrounding rock mass before and after implementing the anchoring system. The results based on an actual tunnel project suggest that the mechanical properties all enhanced in the anchoring tunnel section The elastic modulus of the surrounding rock increased by 45.7%, the cohesive force increased by 18.1%, and the friction angle increased by 2.92%. Hence, the yielding bolt anchor can effectively prevent the squeezing deformation of the surrounding rock mass and improve the structural integrity of the tunnel lining. The performance of the anchoring system and the inversion process of the mechanical parameters can guide the design and construction of similar tunnel projects in weak rock mass configurations.

1. INTRODUCTION
During the excavation progress in a rock tunnel under high in-situ stress, the problem of large squeezing deformation is often encountered in unfavoured geological conditions consisting of weak surrounding rock mass (Liu and Jiang 2021). There is no good treatment to deal with the large squeezing deformation of the tunnel during construction progress, which continuously leads to disasters in tunnel construction. In tunnel squeezing conditions, the supporting structure of the tunnel is complicated to construct, and the rework after the squeezing incident is time-consuming and labour-intensive. Many scholars tried numerical simulations to grasp the actual squeezing deformation characteristics of the surrounding rock during excavation. Nevertheless, most numerical methods cannot match the field monitoring data due to the subjectivity of the selection of rock mechanics parameters, the uncertainty of surrounding geological conditions, the variability of the construction process, and the limitation of mesh distorting in numerical calculation. Therefore, it is practically essential to capture the mechanical parameters of the surrounding rock mass in tunnel construction based on the field measurement data.