bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring the Geometry of Fracture Intersections Under Stress
Authors: Santos A. M. , Hu M. , Pyrak-Nolte L. J.
Published: September 2022

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Fracture networks in rock provide the connected flow paths through which fluids are injected or withdrawn from subsurface reservoirs during energy production (e.g. geothermal, oil & gas, H2 storage) and anthropogenic waste isolation (e.g. CO2 sequestration, nuclear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

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

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

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

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

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

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.
EPOS Thematic Core Service Anthropogenic Hazards - Open-Access Integrated Infrastructures for Research and Innovation in the Area of Anthropogenic Seismicity Associated with the Exploitation of Georesources
Authors: Lasocki S. , Orlecka-Sikora B. , Rudzinski L. , Lelonek M. , Kocot J. , Jones G. , Garcia-Aristizabal A.
Published: September 2022

EPOS Thematic Core Service ANTHROPOGENIC HAZARDS (TCS AH) integrates, within the framework of the European Plate Observing System (EPOS) (www.epos-eu.org), research infrastructures freely open for scientists, engineers, and all others interested in hazards posed by the seismicity induced by geo-resource exploration and exploitation. The integrated infrastructures consist of three components:

•Data gathered in "episodes." An episode is a set of time-correlated geophysical and technological data and other relevant geo-data that comprehensively report anthropogenic seismicity cases and the industrial and geological conditions of these processes.

•Applications, i.e., problem-oriented, bespoke, and standard software tools to process and analyze the data. They help relate seismicity and technological factors for hazard assessment and other scientific targets.

•The episodes and applications are accessible on the EPISODES e-platform (https://tcs.ah-epos.eu), an IT environment for data modeling and analysis. The platform provides the user’s workspace, adequate hardware resources, including HPC systems and other facilities that grant quick and efficient execution of commissioned tasks. Here we present and describe the structure and details of this open-access facility. On an example of the pilot "Time-Dependent Anthropogenic Seismic Hazard Assessment," we demonstrate the potential of the integrated infrastructures for developing innovative practice solutions, ready-for-implementation in geo-resource exploitation.

1. INTRODUCTION

Exploitation of geo-resources alters the stress and strength conditions in the engaged rock mass. In favorable conditions such alterations result in rock fracturing and violent emission of seismic waves. This process known as anthropogenic seismicity is an unwanted response of the rock mass to the technological processes. With rising demands for energy and minerals, anthropogenic seismicity has been appearing in association with diverse technological processes, and often also in previously aseismic regions. The induced or triggered earthquakes can accompany underground and open-pit mining, conventional and unconventional hydrocarbon extraction, geothermal energy production, underground liquid and gas storage including carbon sequestration, impoundment of surface reservoirs of liquids (like artificial lakes of dammed water for hydroelectric plants and ore-floatation waste repositories) and many other technological processes that perturb the boundary conditions in the affected rock (Lasocki and Orlecka-Sikora, 2020).
Dynamic Fracture Network Evolution: Monitoring and Characterizing Using a Geomechanically Constrained Time-Lapsed Windowed Microseismic Imaging
Authors: Gentry E. N. , Soroush H. , Batir J. , Aminzadeh F.
Published: September 2022

To create an efficient subsurface heat exchanger in an Enhanced geothermal System (EGS), it is essential to have a thorough understanding of the subsurface characteristics along with an effective real-time system to monitor and map the changes in induced and natural fractures during stimulation and production. The ability to monitor the variation in fracture network characteristics is necessary to evaluate reservoir performance over time. These continuous assessments provide valuable information and an opportunity to optimize stimulation schemes for maximum heat production. We developed a methodology for analysis of microseismic data through a novel "Time-Lapsed Microseismic" (TLM) technique combined with a Moment Tensor Inversion (MTI) method, to detect, locate and geomechanically characterize microseismic events in different time windows for monitoring the changes in the fracture network’s geometry and geomechanical status over time without requiring additional data acquisition or monitoring tools. 41 years of raw waveform data from multiple generations of seismic networks from the Geysers geothermal field were amalgamated to generate a catalog of 9,601 stable full-waveform MTI solutions in a rapid time frame. The resulting TLM data are the foundation for monitoring the temporal changes in fracture characteristics. Furthermore, as new microseismic data are collected, the TLM volume is updated, rendering itself to become a primary EGS monitoring tool.

1. INTRODUCTION

The long-term productivity of an EGS is controlled by the temporal evolution of induced fractures in geothermal reservoirs because the fracture network is the path by which heat (resource) is extracted from the subsurface. Therefore, it is essential to monitor the variation in fracture network characteristics over time to assess reservoir performance. These updated assessments provide valuable information and an opportunity to optimize stimulation schemes for maximum heat production.

To monitor fracture evolution through time, geomechanically analyzing these unexpected reservoir behaviors is needed to better understand the reservoir dynamics and the role of hydraulic shearing, which can potentially alter the near-well and far-field permeability structure (Soroush et al., 2018). One of the readily available datasets for subsurface monitoring is microseismic monitoring. If the signature of hydraulic shearing of fractures (which are the main sources of microseismicity) in microseismic data can be captured, then identification and characterization of fracture evolution can be automated using artificial intelligence. Therefore, the integration of advanced geophysical and geomechanical analysis workflows, augmented by artificial intelligence, seems to have vast potential in providing low-cost solutions for monitoring fractures’ evolution and conductivity in real-time.
Waveform Similarity of Micro-Seismicity at the ToC2ME Hydraulic Fracturing Experiment Site
Authors: Yang Jin , Li Bing
Published: September 2022

This study quantitatively investigates the waveform similarity of micro-earthquakes detected during the Tony Creek Dual Microseismic Experiment (ToC2ME) conducted near Fox Creek, Alberta. Subsurface anthropogenic activities, especially processes involving injection, can lead to accumulation of pore pressure and elastic strain among the geologic formations and rocks, resulting in induced earthquakes. Four hydraulic-fracturing treatment wells were stimulated in the middle of the study area. An acquisition system monitored continuous seismic waveforms from 25 October to 15 December 2016 revealing 4083 hydraulic fracture-related events with magnitude ranging from Mw from -1 to 3.2. The present study compares and discusses similarity of waveforms captured by these stations using the PageRank method to form families of similar waveforms and rank their relative importance within their family. Waveforms corresponding to earthquake events are extracted from 3 representative stations for analysis. Preliminary results reveal earthquake families spatially gathered around the injection wells. Of the three main clusters located in the center, west, and east of the well, the central cluster showed the widest range of PageRank values, and also contained the highest PageRank value events. Events that happened before injection programme are more likely to have high PageRank values. There is also a slight positive correlation between PageRank value and magnitude. Overall, early events have more direct or indirect links than subsequent events.

1. INTRODUCTION

Documented earthquakes events in North America have shown a dramatic increase in the past two decades, especially in northwestern and southern United States and western Canada. Previous research notes the emergence of small-scale earthquakes that are closely related to human activities, especially hydraulic fracturing and saltwater disposal (Atkinson et al., 2014, Konstantinovskaya et al., 2021, Schultz et al., 2020). This can partially be attributed to the implementation of improved monitoring technologies with higher capability for capturing earthquake events below a local magnitude (ML) of 2.5, denoted as micro-earthquakes.
How Static Stiffness Is Affected by Non-Elastic Deformations in Different Lithologies
Authors: Lozovyi S. , Fjær E. , Mews K. S. , Giger S. B.
Published: September 2022

The purpose of this work is to study the evolution of non-elastic deformations and their effect on static stiffness prior to reaching plastic yield. To this end, a series of geomechanical laboratory experiments on preserved rock cores of various lithologies is performed. The experiments include probing of static stiffness on saturated core samples in loading-unloading undrained cycles. Test results are used to obtain parameters that describe the non-elastic response of stress-strain relation. Further, the non-elastic parameters are implemented in an empirical model to evaluate the dependence of stiffness on applied triaxial stress amplitude. Results show that for almost all tested rocks, Young’s modulus and Poisson’s ratio are dependent on stress change during triaxial loading/unloading well before reaching plastic yield. In order to study the factors influencing non-elastic processes, correlations between the computed non-elastic parameters and rock properties such as porosity, mineralogy and stiffness were established.

1. INTRODUCTION

It is known that rocks are not linear elastic media and deviate from purely elastic response already at micro-strain level (Winkler et al. 1979). However, in practical geomechanical applications, linear elasticity is often assumed until the strain reaches plastic yield. This assumption may lead to false predictions of stress-strain changes in the subsurface during e.g., hydrocarbon reservoir depletion or injection, geotechnical operations, or long-term nuclear waste storage. In laboratory rock-mechanical test results, stiffness is usually reported as constant values, independent of stress/strain amplitude changes. However, using only a few additional parameters, non-linearity can be addressed by linearizing the compliance function versus stress for static loading/unloading as described below.

In soil mechanics, Kondner (1963) demonstrated that a hyperbolic function can approximate non-linear stress-strain curves for both sand and clay with a high degree of accuracy. On transformed axes, hyperbolae can be plotted as a linear function. Therefore, non-elastic behavior can be described by only two coefficients a and b. a is the inverse of the initial tangent modulus, and b is the inverse of the asymptotic value of the stress difference, which the stress-strain curve approaches at infinite strain.
Verification of a Distributed Fiber Optic Sensing Slope Stability Monitoring Solution
Authors: Clarkson P. , Cole S. , Godfrey A. , Crickmore R. , Minto C. , Watlet A. , Whiteley J. , Chambers J. , Boyd J. , Dashwood B.
Published: September 2022

This paper describes the testing of a novel ground condition and slope stability monitoring system based on Distributed Rayleigh Sensing (DRS) on a landslide observatory operated by the British Geological Survey (BGS). The DRS system uses the backscattered light from buried fiber optic cables to determine the strain and temperature at any point along the fiber up to distances of over 50 km and has been shown to respond to ground movement, moisture content changes and temperature variations. The output of the fiber is compared to that expected based on the known geology of the slope and other instruments such as tiltmeters and moisture content sensors. In addition to long-term strain and temperature measurements, the system can also sense acoustic vibrations and can be used to make active and passive seismic surveys to give a comprehensive 3D picture of the subsurface state. The results show that the DRS system can provide improved spatial and time resolution and sensitivity to give a more comprehensive and detailed picture of slope behavior than would otherwise be possible. Such detail allows improved landslide prediction methods and early warning systems to be developed.

1. INTRODUCTION

Slope stability monitoring is important for failure detection and prediction and for greater understanding of slope behavior. Slope stability depends on several slope characteristics and there are a wide range of measurement methods that can increase such understanding. Fiber optic based sensing approaches are widely used for infrastructure monitoring and are increasingly being used for structural integrity and slope stability assessment due to their high sensitivity and spatial coverage and resolution. Such systems usually either operate at acoustic frequencies (as in Distributed Acoustic Sensing (DAS) systems) or at lower frequencies as Distributed Strain Sensing (DSS) systems. DAS systems operate by monitoring phase changes in Rayleigh backscattered light from pulses transmitted down an optical fiber. These phase changes occur due to small strain and temperature induced variations in the refractive index of the fiber. Most systems based on Rayleigh sensing are AC coupled to strain and are not used to perceive strain changes over longer timescales. As such, they have primarily been used for event detection and until recently had limited applicability for longer term condition monitoring and event prediction. However, recent advances in the technology have enabled absolute strain changes to be measured over much longer timescales using Distributed Rayleigh Sensing (DRS) systems. This leads to a wider range of applications, for example slope stability monitoring.
An Experimental Study of Fracture-Induced Chemical Reactions
Authors: Carey J. W. , Frash L. P. , Hicks W. , Menefee A. H.
Published: September 2022

Fracturing of rock allows ingress of fluids that may be chemically distinct from native pore fluids. These external fluids can induce dissolution and precipitation, which may be enhanced by highly reactive, comminuted material and metastable highly deformed materials. Reaction products have important feedbacks via dissolution of asperities that affect fracture strength and friction properties. In this study, we examine dynamic fracturing of anhydrite/dolomite using triaxial direct-shear experiments with simultaneous x-ray radiography and tomography. The impermeable cores were fractured at a temperature of 50°C and a confining pressure of 3.5 MPa while being exposed to 500 kPa injection pressure of concentrated (18 wt%) BaCl2 solution. Once fractured, the barium solution invaded the primary shear fracture and the surrounding damaged region. X-ray radiographs and tomography revealed precipitation of barium sulfate and carbonate (barite/witherite). Despite the precipitation, the permeability of the fracture system changed little following the initial fracturing event. Precipitation was likely confined to relatively stagnant flow regions, with more open regions sustaining high flow rates. The experimental results demonstrate laboratory-induced fluid-rock reaction and precipitation in fracture systems and reveal the important role of grain-scale mineralogy and flow pathways on the extent of reaction and the impact of precipitation on permeability.

1. INTRODUCTION

Fracturing of rock allows the ingress of fluids that may be chemically distinct from the native pore fluids. These external fluids can induce chemical reactions that are extremely challenging to anticipate or monitor, as they are a complex function of both intermixing among external and native fluids and reactions with the mineralogy of the host rock. The primary reactions of interest are dissolution of primary minerals and precipitation of secondary minerals, which can alter both fracture and void space sufficiently to change critical transport and rock mechanical properties (e.g., Viswanathan et al. 2022). The fracturing process itself can produce highly reactive, comminuted material that can accelerate these types of geochemical reactions. In addition, the complex geometry of fracture systems creates large variations in the ratio of reactive surface area to fluid volume (i.e., tensile opening versus closed shear; Menefee et al. 2020). Furthermore, fracturing under intense shear can generate highly reactive, metastable materials (e.g., heavily deformed crystals, amorphous material, glass) that lead to non-equilibrium precipitates. Such reaction products have important implications for the hydraulic and mechanical evolution of geologic systems, but their formation and growth depend on an array of widely variable reservoir conditions (e.g., geochemistry, mineralogy, temperature/pressure, flow rate, permeability) and thus are poorly constrained.
Correlation of Near Surface Geotechnical and Geophysical Parameters for Six Bridge Sites in Central Montana
Authors: Barrick D. J. , Link C. A. , MacLaughlin M. M. , Berry S. M.
Published: September 2022

Results are presented from tests performed for the replacement of six timber bridges in Central Montana. The sites consist of Cretaceous sedimentary rocks overlain by thin layers of residual clays or Quaternary alluvium. Samples of the overlying materials were collected to supplement 43 core and Shelby tube samples from borings. Laboratory tests were performed resulting in values for static modulus, moisture content, unit weight, and peak compressive strength. Geophysical investigations were also completed at the site using four methods: refraction tomography (SRT), shear-wave analysis (MASW), electrical resistivity tomography, and induced polarization tomography. Geophysical values were extracted from the final 2D tomogram and compared with geotechnical borehole data at the same depths. These geophysical and geotechnical values were used as inputs and targets in a Feedforward Neural Network (FNN). The goal of the FNN analysis is to determine whether a relationship can be mapped between the geophysical and geotechnical values. Such a relationship would allow future investigation via nondestructive experimental techniques and provide confidence in using geophysical site investigations where geotechnical drilling cannot be performed. Our results from FNN analysis suggest a high confidence of predicting common geotechnical parameters from independent geophysical data for sedimentary rocks in Central Montana.

1. PROJECT BACKGROUND AND GOALS

This study was conducted during a geotechnical site investigation for replacement of six timber bridges between Lewistown and Grass Range, Montana on Highway MT-200. The limits of the locations of the bridges (numbered 5991, 5992, 5993, 5995, 5996, and 5997) are shown in Figure 1. These small timber bridges exist in topography that is considered level terrain with the existing highway grades generally ranging from 0-3%. The bridge sites are in a rural, agricultural area with no surrounding developments. The timber structures were originally constructed in the 1930’s and are in fair to poor condition. The bridges act as a crossing for continually flowing streams or as underpasses for livestock. While the primary intent of the geotechnical investigation is to estimate subsurface conditions for proposed new bridges or box culverts, the project presented the opportunity to collect data for identifying potential correlations between engineering and geophysical parameters of the materials.
Static and Dynamic Mechanical Properties of Rock at Elevated Temperature
Authors: Mitra A. , Djordjevic O. , Thombare A. , Govindarajan S. , Gokaraju D. , Aldin M. , Patterson R. , Simone A.
Published: September 2022

Knowledge of mechanical properties of subsurface at elevated temperature is crucial to understand a range of processes in the earth’s crust and in building geomechanical models to assist in operating geothermal systems, nuclear waste repository, CO2 sequestration and hydrocarbon extraction. Although there exists sufficient literature reporting measurement of static mechanical properties on a range of rock types at elevated temperature, reported values for ultrasonic velocities are extremely limited. This in turn presents a challenge for the dynamic-to-static conversion of mechanical properties, a pivotal step in building geomechanical model. This paper presents the results of a laboratory study utilizing Berea and Upper Gray Berea sandstone and mudstone samples from a producing US reservoir at 75°C. A decrease in both P and S wave velocity with temperature is observed in a Berea sample. A decrease in static Young’s modulus is observed in mudstone samples from two clay-rich reservoir intervals with one of the reservoir intervals demonstrating significant static and dynamic anisotropy. Additionally, the samples from both intervals mimicked the response of Berea for dynamic mechanical properties under constant hydrostatic stress. This study is intended to provide better representative inputs for improving the accuracy of subsurface characterization and geomechanical models for aforementioned applications.

1. INTRODUCTION

The knowledge of mechanical properties of rock at elevated temperature is crucial to understand and model a number of processes in the earth’s crust (Heuze, 1983). Such information also adds value in designing high-level nuclear waste disposal (Klett, 1974). In the oilfields, high-temperature operating environment is frequently encountered in deepwater operations (DeBruijn, 2008) and heavy oil reservoirs (Curtis, 2002). Chen and Ewy (2005), for example, observed that heating the wellbore increases both the collapse and fracture pressure gradient. For geothermal energy recovery, high temperature is a common challenge for drilling (Meng et al., 2019). Finally, for CCUS, CO2 need to be injected beyond a certain temperature to ensure supercritical condition. All of these requires a deep understanding of mechanical properties of rock at elevated temperature.
Stress Evolution of a Geological Nuclear Waste Repository in a Creep-Prone Shale Formation
Authors: Sasaki T. , Rutqvist J.
Published: September 2022

This study investigates the effect of shale creep on the stress evolution of a generic nuclear waste repository. Thermo-hydromechanically (THM) coupled simulations were carried out with the TOUGH-FLAC simulator to model temperature/pore pressure/stress changes due to the decay heating from nuclear waste. The Norton-Bailey creep model, which was calibrated against published creep experiments on shale, was used to simulate different creep properties of shale (i.e., no creep vs. creep). Results show that shale without creep generated and maintained high stress concentrations (~40 MPa) near the disposal tunnel for an extremely long period (~10,000 years), whereas shale with creep dissipated the stress concentrations and developed uniform and isotropic stress field of roughly 12 MPa (in compression), which corresponded with the overburden stress level at the tunnel depth, by as early as 100 years since the emplacement of nuclear waste. Also, it was found that shale with creep increased compressive stresses in the bentonite backfill compared to shale without creep by as much as 130% at 10,000 years due to creep-induced tunnel volume reduction.

1. INTRODUCTION

A permanent solution to accumulating nuclear waste will be geological nuclear waste repositories (IAEA, 2003). Geological repositories confine nuclear waste deep underground to protect the biosphere with a multi-barrier system (Apted & Ahn, 2010). The barrier system consists of natural barriers (i.e., formations) and an engineered barrier system (EBS) (e.g., bentonite backfill), which is placed around nuclear waste canisters in the disposal tunnel. The EBS not only provides mechanical support to the nuclear waste canister but also enhances the stability of the formation around the tunnel, which could be damaged during tunnel excavation (Rutqvist, 2015). The excavation damaged zone (EDZ) could provide flow paths for radionuclides if they are released (Tsang et al., 2005). Hence, it is crucial to evaluate the stability of the EBS, EDZ, and surrounding formation for the long term in order to assess the safety of geological nuclear waste repositories.
Study on Rock Breaking Mechanism and Optimization of PDC Cutter for Deep Water HTHP Plastic Mudstone
Authors: Chen Haodong , Liu Hexing , Han Xu , Jin Yan , Liang Jiwen , Wang Shiguo , Lu Yunhu
Published: September 2022

Mudstone with high clay content was developed in the deep stratum of a deep-water block in the South China Sea. During drilling, under the action of the high-density drilling fluid hydrostatic column pressure, the mudstone stratum presents hard-plastic characteristics. It is difficult for the PDC bit cutters to penetrate the stratum, resulting in low ROP. In response to the above problems, the rock mechanics experiments of downhole mudstone were carried out. The numerical model of the PDC cutter cutting mudstone was established to analyze the influence of the PDC cutter parameters on the rock-breaking efficiency. Studies have shown that the rock-breaking efficiency of the non-planar cutter is better than that of the planar cutter; the rock-breaking efficiency of 16 mm diameter cutter is better than that of 19 mm diameter cutter; as the back dip angle of the PDC cutter increases, the rock-breaking efficiency of PDC cutters decreases. Personalized PDC bits suitable for this block have been selected through the above research. The field application shows that the ROP has improved greatly compared with the adjacent wells. The research provides theoretical and technical support for the efficient drilling of deep-water plastic mudstone in this block.

1. INTRODUCTION

A deep-water block in the western part of the South China Sea, with a water depth of 850~990m, has complex and variable formation pressure, with the maximum formation pressure coefficient reaching 2.38 g/cm3, and complex mudstone development in the deep strata. During drilling, the mudstone formation shows high strength and plasticity under the action of high-density drilling fluid hydrostatic column pressure, which makes it difficult for the PDC cutter to penetrate the formation, resulting in a decrease in rock-breaking efficiency, the average ROP is only 5.6 m/h, and the drilling cycle is long, which seriously restricts the exploration and development process.
Impact of Spiritual Intelligence and Resilience on Self-Efficacy of Nurses in the Pervaiz Ilahi Institute of Cardiology
Authors: Anam Iqbal  , Mubashar Ahmad  , Irum Qureshi  , Tahmeena Batool  , Misbah Iqbal
Published: September 2022

The Aim of the research work is to find the Impact of Spiritual Intelligence and Resilience on Self-Efficacy among Nurses in the Pervaiz Ilahi Institute of Cardiology Hospital Multan. A quantitative research design used in survey method by using questionnaire to obtain data. The sample was calculated through G* Power and consisted of N = 184 nurses, data is collected from Pervaiz Ilahi Institute of Cardiology Hospital Multan. Researcher used convenient sampling techniques to collect data according to the age, income, marital status and the job level along with three scales. First scale was Karadeniz and Aydin’s (2016) Spiritual Intelligence Questionnaire (SI), higher level of score shows higher spiritual intelligence and the second scale was Wagnild & Young’s (1993) The Resilience Scale (RS) and higher scores indicate higher resilience. Third scale used was Paulhus’s (1997) personal efficacy scale. The results show that there is significant impact of spiritual intelligence on nurses’ resilience. In other words, spiritual intelligence predicts resilience. The results also showed that there is no significant difference, between unmarried and married nurses on the scale of spiritual intelligence, and resilience and there are no “significant differences” find in term of experiencing among nurses.
ANALISIS PENENTUAN BESARAN DAN PENGELOLAAN DANA DESA (Studi Kasus Kesesuaian Penentuan Besaran dan Pengelolaan Dana Desa Dengan Peraturan di Kecamatan Omben Kabupaten Sampang)
Authors: Moh. Syarif  , Amurroin An
Published: September 2022

Dana Desa adalah dana yang bersumber dari Anggaran Pendapatan dan Belanja Negara (APBN), yang diperuntukkan bagi Desa yang ditransfer melalui Anggaran Pendapatan dan Belanja Daerah kabupaten/kota dan digunakan untuk membiayai penyelenggaraan pemerintahan, pelaksanaan pembangunan, pembinaan kemasyarakatan, dan pemberdayaan masyarakat.

Penelitian ini menggunakan metode kualitatif, dengan prosedur penelitian yang menghasilkan data deskriptif berupa kata-kata tertulis atau lisan dari orang-orang dan perilaku yang dapat diamati. Fokus penelitian yang dilakukan oleh peneliti yaitu untuk  mengetahui kesesuaian penentuan besaran dan pengelolaan Dana Desa dengan peraturan di Kecamatan Omben Kabupaten Sampang.

Dari hasil penelitian, ditemukan bahwa penentuan besaran Dana Desa masih ada ketidak singkronan data yang dimiliki oleh desa dengan sejumlah data yang diterima oleh tim yang merumuskan penentuan besaran Dana Desa untuk masing-masing desa di Kabupaten Sampang, khususnya Kecamatan Omben
DAMPAK PEMBANGUNAN OBYEK WISATA TERHADAP TINGKAT PENDAPATAN PENDUDUK LOKAL (STUDI KASUS WISATA DESA DARAMISTA SUMENEP)
Authors: Sayyidi  , Kurniawati Lilis
Published: September 2022

Keberadaan objek wisata tidak lepas dari perkembangan ekonomi lokal yang meningkatkan aktivitas ekonomi di kawasan tersebut, termasuk peningkatan daya tarik objek wisata. Keberadaan objek Bukit Tinggi memiliki banyak kontribusi terhadap perekonomian daerah. Pembangunan ekonomi yang timbul dari objek Bukit Tinggi dapat mendorong terciptanya peluang kerja dan meningkatkan ekonomi masyarakat sekitar. Sehingga bisa memicu pembangunan berkelanjutan regional. Tujuan dari penelitian ini adalah untuk mengetahui dampak ekspansi pada objek Bukit Tinggi terhadap pengembangan ekonomi lokal di Kabupaten Sumenep. Untuk menjawab pertanyaan-pertanyaan ini, penelitian ini menggunakan metode deskriptif kualitatif dan lokasi penelitian ini pada objek Bukit Tinggi di Kabupaten Sumenep. Fokus dalam penelitian ini adalah dampak ekspansi pada objek Bukit Tinggi terhadap pengembangan ekonomi lokal di Kabupaten Sumenep. Metode pengumpulan data yang digunakan dalam penelitian ini adalah metode observasi, wawancara mendalam dan dokumentasi.