bluuebunny/crossref_metadata_2025 huggingface dataset:
Geological Feature Extraction and Data-Driven Production Prediction Based on Well Logging Data
Authors: Hsu Maoya , Ma Zhengchao , Tian Shouceng , Zhou Xiaoxia , Dai Jiacheng , Weng Jintao , Wang Tianyu
Published: August 2024

Data-driven fracturing production prediction relies on geological engineering parameters to forecast production indicators. These parameters are traditionally derived from manual summarization and statistical analysis of well logging curves, potentially leading to inaccuracies due to incomplete encapsulation of formation complexities. This research, however, employed objective recorded data to enhance data credibility. Leveraging a convolutional neural network model, precise production predictions were achieved through the extraction of abstract features from the logging data. The study utilized the Gram angle field method for two-dimensional transformation of sequence data, preserving overall data coherence. By incorporating engineering parameters into deep neural network models or integrated learning models, the study facilitated production prediction, validating the correlation between formation characteristics and production. The study also explicated the convolutional network's operational mechanics, resulting in the development of a novel geological parameter description scheme. Notably, substituting manual statistical data with objective well observation data significantly enhanced the model's predictive accuracy and robustness. Ultimately, this research introduces an intelligent model that integrates well logging data for data-driven production forecasting, optimizing workflow processes through the extraction of critical information from raw data.

1. INTRODUCTION

Production forecasting in oil and gas extraction is a critical task that affects operational strategies and investment decisions in the industry. Artificial intelligence methods have been widely applied to scenarios such as production forecasting due to the accumulation of oilfield data and the advancement of machine learning methods (Lolon et al., 2016). Machine learning models can overcome the limitations of traditional analytical methods in correlating high-dimensional data due to their powerful nonlinear fitting capabilities (Pankaj et al., 2018). Various machine learning models have been used by researchers, including artificial neural networks (ANN) (Clar et al., 2019), imperialist competitive algorithm (ICA) (Berneti et al., 2011), higher order neural networks (HONN) (Chakra et al., 2013), nonlinear autoregressive neural networks (NARX) (Sheremetov et al., 2014), and multivalued neuron complex neural networks (MLMVN) (Aizenberg et al., 2016). A fusion model of a multilayer perceptron (MLP) network (Shi et al. 2021) and a long-short-term memory (LSTM) network (Wang et al., 2021) was constructed to predict production using geological and fractured reservoir parameters, historical data, and other metrics (Mohd Razak et al., 2021).
Control Technology of High Prestress Excavation Compensatory Support in Tunnels Through Fault Fracture Zones
Authors: Sun Jihao , Yang Xiaojie , He Manchao
Published: August 2024

Taking the Tabaiyi tunnel in Yunnan Province as the research background, the tunnel has suffered from disasters such as large deformation of initial support, deformation of steel arches, and mud and water inrush under the original support conditions. According to the theory of excavation compensation and the requirements of traffic tunnel engineering on the anchorage system, this paper proposes a high prestressing anchorage system applicable to large deformation tunnels traversing fault fracture zones and capable of realizing the concept of timely support, and the application of the supporting technology is carried out in the experimental study. Based on the resin anchorage that can be prestressed after the rapid condensation of the overrun double-gradient grouting reinforcement, the rapid prestressing NPR anchorage system of "overrun grouting+resin anchorage" and its supporting active support technology system are proposed. The results of the field experiment show that: under the implementation of double gradient grouting and NPR anchor cable timely active support system, the effect of large deformation control is remarkable, and the large deformation of surrounding rock is effectively controlled within 300mm, which verifies the superiority of the deformation control technology based on rapid prestressing anchorage support in large deformation tunnels through the fault fracture zone.

1. Introduction

With the quick development of underground engineering in recent years, the construction of railway, highway, and water conservancy tunnels in China has also developed rapidly. Among them, there is no lack of some tunnels through fault fracture zones, which are prone to risky disasters such as large peripheral rock deformation, water and mud inruch during the construction process (Jiang (2023) and Chen (2023)). Taking the Jian-ge-yuan Expressway tunnel as a typical example, the Tabaiyi tunnel is one of the high-risk tunnels along the whole route. The length of the tunnel is 2.6 kilometers. The cross-section area is close to 140 m2. The construction took five years, and some sections of the tunnel still showed deformation, cracking, falling block misalignment, arch rise, and other phenomena after the second lining was poured. Therefore, the construction of the Tabaiyi highway tunnel is one of the most difficult problems in the world of tunneling.
Transient Effects of Time-Dependent Drilling Fluids on Wellbore Stability
Authors: Ma Y. , Dokhani V. , Miao H. , Geng T. , Shi Z.
Published: August 2024

Accurate prediction of dynamic pressures is essential for wellbore integrity analysis in deep water wells and wells with narrow operational windows. During the start-up of circulation, a higher circulating pressure is needed due to the gelation effect of drilling fluid. A coupled poro-elasto-dynamic model is developed to examine the effects of pump start-up on borehole stability. Firstly, a transient hydraulic model is developed to predict the temporal variation of pressure in flow conduits during the pump ramp-up periods. A constitutive equation is used to describe the time-dependent rheology of gelled fluid. The hydraulic model is then coupled with a wellbore stability model to study the effect of dynamic pressures on wellbore integrity. The method of characteristics is employed to solve the governing equations of the hydraulic model. Failure analysis is performed to evaluate the gelation effect of drilling fluid and pump ramp-up on borehole stability. The results of the hydraulic model are validated through comparison with field data and that of a published study. The results indicate that maximum circulating pressure is initially attained before approaching an equilibrium circulating pressure. A time-dependent failure can occur in the vicinity of the borehole depending on the magnitude of gel strength and pump ramp-up speed. The study concludes that by ignoring the time-dependent characteristics of drilling fluids the magnitude of circulating pressures in early times can be underestimated. Therefore, an integrated framework is suggested to consider the time-dependent effects of drilling fluids on circulating pressure and hence wellbore stability. The developed poro-elasto-dynamic model can be utilized to improve our understanding of the transient effects of drilling fluids on wellbore stability.

1. INTRODUCTION

Drilling hydraulics is one of the most important factors to control the safety of drilling operations. It has received special attention in the past through downhole measurement tools to improve downhole pressure monitoring. However, it is not possible to deploy such tools in sensitive and risky areas. In addition, it is required to have a reliable hydraulic model to predict downhole pressure for design purposes. Several hydraulic models have been developed to estimate the frictional pressure losses during drilling fluid circulation under steady-state conditions (Reed and Pilehvari, 1993; Merlo et al. 1995; Mitchell and Miska, 2011). The major rheological models to describe the pressure losses in pipe and annuli include the Bingham-Plastic, Power-law, and Yield Power-law (Herschel-Bulkley) model. Drilling fluids generally exhibit thixotropic behavior due to their mixture composition (Bourgoyne et al. 1990). Nevertheless, the fluid gelation and thixotropic effect are not commonly considered in the majority of the abovementioned studies.
The Sunset Solution: Closure on Leaking Proppant
Authors: Peirce A. P. , Abbas S. , Detournay E.
Published: August 2024

Recent analytic work (Peirce and Detournay, 2022a) has established the tip asymptotics for receding hydraulic fractures that close due to leak-off to the permeable rock. This asymptotic result enabled the development of rigorous numerical schemes to explore the recession dynamics of hydraulic fractures that develop in a state of plane strain (Peirce and Detournay, 2022b) and radially symmetrically (Peirce, 2022). These detailed studies enabled the identification (Peirce and Detournay, 2022c) of the so-called Sunset Solution, which is a similarity solution that emerges close to the ultimate collapse of the fracture. The asymptotic analysis performed in (Peirce and Detournay, 2022c) establishes that the existence of the sunset solution is due to a fundamental decoupling of the kinematics from the dynamics in the governing equations, which leads to a robust way to measure the Carter leak-off coefficient from the rate of change in the fracture aperture at the wellbore. These results were established assuming that no fluid is leaking from the closed section of the fracture. In this paper, we explore the viability of the procedure to estimate the Carter leak-off coefficient using the sunset solution when the fracture is assumed to close on proppant that is filled with fluid upon closure and which continues to leak off and exchange fluid with the open portions of the fracture.

1 INTRODUCTION

The diagnostic fracture injection test (DFIT) is used in petroleum engineering to assess the minimum in situ stress, Carter's leak-off coefficient, and other reservoir parameters. The test consists of monitoring the well pressure during injection of fluid over a time long enough to create a hydraulic fracture, as well as after shut-in of the well. Interpretation of the pressure decline that follows the end of pumping was pioneered by Nolte (1979, 1986). His original analysis relies on two main assumptions: (i) the fracture stiffness remains constant after shut-in until the fracture completely closes and (ii) Carter's leak-off coefficient CL is a constant. In Nolte's analysis, the coefficient CL is interpreted from the pressure decline following the sudden drop of pressure observed when the well is shut-in, by expressing the declining pressure as a linear function of G(Δt), which is a function of Δt - the time elapsed since shut-in divided by the shut-in time ts (Nolte, 1979, 1986).
Intact Rock Properties of the Rotondo Granite for the PRECODE Project in the BedrettoLab
Authors: Perras M. A. , Golabchi Y. , Bahrani N. , Hamdi P. , Amann F.
Published: August 2024

In order to estimate the depth of the Excavation Damage Zone (EDZ) using empirical or numerical approaches, the key intact properties include the Uniaxial Compressive Strength (UCS), the tensile strength, and the crack initiation threshold. In addition to these test derived values, plotting triaxial test results and determined Crack Initiation values from those tests can help to define Damage Initiation and Spalling Limit failure envelops for numerical modelling of brittle behaviour. In order to predict the extent of the EDZ in the Rotondo granite around a mine-by tunnel being excavated as part of the PRECODE project in the BedrettoLab, Switzerland, a testing program has been conducted. It was found that the static Young's modulus was 52.5 GPa, that the Poisson's ratio was 0.22, that the Direct Tensile Strength reduced from the Brazilian Tensile Strength by a factor of 0.86 was 6.0 MPa and the UCS was 180.9 MPa. In addition, triaxial tests with confinements up to 20 MPa were conducted to determine the intact Hoek-Brown failure envelop, with a mi of 36. These laboratory derived values will be used to predict the EDZ depth and compare it to the measured EDZ from the PRECODE mine-by tunnel in the future.

1. INTRODUCTION

Development of brittle damage around underground excavations in highly stressed conditions is a common phenomenon. For deep geological repositories, interest in brittle damage studies began in mid-1980's (Kelsall et al. 1984) with a focus on determining the changes in permeability due to blasting. Much research has since been conducted on various topics related to the development of Excavation Damage Zones (EDZ) for nuclear waste repositories (see Alcaino-Olivares et al. 2024 for details). However, only until more recently has the focus in rock mechanics turned back to time-dependent behaviour of brittle rocks with a related focus on the long-term behaviour of deep geological repositories. Time-dependent brittle fracturing may lead to an interconnected fracture network that could enhance and, in the framework of nuclear waste disposal, may provide preferential pathways for radionuclide migration. Therefore, a comprehensive understanding of brittle fracturing requires a spatial and temporal characterization of the EDZ. A crucial input into characterizing the EDZ are the intact rock mechanical properties, in particular the Crack Initiation (CI) value which has been shown to be a useful intact rock parameter to determine the depth of brittle failure around excavations (Diederichs 2007). This study examines preliminary rock testing results for input into the characterization of the Rotondo granite for the PRECODE project at the BedrettoLab in Switzerland.
Improve Mechanical Earth Model Calibration Using Statistical Concepts
Authors: Ray P.
Published: August 2024

Mechanical Earth Model (MEM) has a broad impact on drilling, completion, production, and reservoir management decisions. For example, wellbore stability calculated using a MEM can provide safe mud windows for drilling, thereby reducing wellbore instability related non-productive time and drilling costs. A MEM can also provide safe injection limits for CO2 storage, enhanced oil recovery, and wastewater injection.

The process of building and calibrating a MEM often involves collecting and analyzing offset well drilling observations, such as leak-off tests (LOT), diagnostic fracture injection test (DFIT), breakouts (BKOUT), and drilling induced tensile fractures (DITF) along with mud weights used. This process can be time-consuming and challenging because of the large number of wells available for review within a field and the difficulty of finding a single solution that provide best matches for all observations. This process requires multiple iterations and is based on minimizing the error between the model and data. The process can also be subjective due to the lack of sufficient information. This paper demonstrates how statistical tools can be leveraged to streamline and reduce subjectivity of the calibration process.

1. INTRODUCTION

The process and procedure for building a MEM are well documented (Goodman & Connolly, 2007; Plumb et al., 2003; Ray et al., 2007). One of the key components in building a one-dimensional mechanical earth model (1DMEM) is to estimate the magnitudes of horizontal stresses. The horizontal stresses for an isotropic formation are commonly calculated using the following equations:

(equation)

(equation)

Where:

σ h = minimum horizontal stress.

σ H = maximum horizontal stress. σv = vertical stress (overburden). ν = Poisson's ratio.

E = Young's modulus.

α = Biot's coefficient.

Pp = pore pressure.

εh = tectonic strain in the minimum horizontal stress direction.

εH = tectonic strain in the maximum horizontal stress direction.

To solve Eq. (1) & (2), the tectonic strains in both (minimum and maximum) horizontal directions is required, however, these parameters cannot be measured directly. Generally, tectonic strains are estimated from stress measurements, such as leak-off tests (LOT) or diagnostic fracture injection tests (DFIT), however these tests only measure the minimum horizontal stress. Consequently, there are infinite possible combinations of minimum and maximum tectonic strains that can fit the LOT and DFIT measurements. Figure 1 illustrates five MEMs with different combinations of minimum and maximum tectonic strains that all match the DFIT measurement yet produce different tectonic stress regimes. Models 1 and 2 are characterized by an extensional stress regime, Models 3 and 4 by a mix of extensional and strike-slip stress regimes, and model 5 by a strike-slip stress regime.
Micro-Seismic Monitoring in Mines Benefits and Limitations
Authors: Rebuli D. B.
Published: August 2024

Seismic monitoring is a useful tool in understanding the rockmass response to mining. The waveforms recorded by sensors contain information not only about where and when a seismic event occurred but also about the driving stresses, failure mechanism and the intervening rockmass. It is also good to understand the limitations of this tool as they should guide the system design, overall monitoring objectives and the analysis of the seismic data. This paper discusses what information can be extracted from a mine seismic system, how this information can be useful to the mine in understanding their rockmass interaction with mining, but also the limitations associated with this information. Only then can the data be interpreted correctly.

1 INTRODUCTION

Seismic monitoring in a mining environment is a unique tool, in that it is continuous in time and can monitor a 3D volume. It is also a powerful tool, in that it can monitor ground motions over multiple orders of magnitude. For example, in the velocity domain, the sensors can measure ground motions from fractions of μm/s to tens of mm/s. The commonly used magnitude scales, which are logarithmic scales, typically extend from around −2.0 to +2.5 for mining applications, which is at least four orders of magnitude. The sources of the measured ground motions can be many and will be discussed below, but the main objective is to monitor sudden inelastic deformations as a result of stress changes in the rock mass due to mining. This gives a powerful monitoring tool, but it is still just one of many tools available to rock mechanic practitioners.

One of the first questions when contemplating or designing a seismic system should be "What is the objective?". Mendecki et al. (1999) describes seismic monitoring as enabling the quantification of exposure to seismicity. They then list a number of specific objectives, namely location of potential rockbursts, prevention, control, warnings and back-analysis. Identifying the objectives is important, as it will determine such details as which sensors to use, how many and how dense a seismic array is needed and what type of alerts are required.

This paper will not go into too much detail about seismic monitoring systems and array design, except where needed to clarify a concept. However, a short introduction to seismic sources and sensors is useful.
A New Approach to Model Irregular Particles Breakage with Deploying Image Analysis Techniques on Discrete Element Method
Authors: Amir Hosseini M. , Tahmasebi P.
Published: August 2024

While the conventional Discrete Element Method (DEM) is a popular tool for investigating breakage, it falls short of accurately capturing the natural morphology of particles. Moreover, previously introduced techniques for simulating irregular particles' breakage have simplified the breakage into only two splitting and chipping mechanisms, which tend to depict fractures as linear or planar. To fill the research gap, therefore, we have introduced an innovative 3D breakage model that incorporates the actual shape of grains and all key breakage mechanisms, including splitting, chipping, and fragmentation. To consider all fracture mechanisms in our simulations, we deploy Dijkstra's algorithm within the particle's stress field to obtain the fracture surface(s). Following the identification of these fracture surface(s), we employ intersection set operations and a labeling technique to generate multiple sub-grains. To demonstrate the accuracy of our approach in modeling breakage, we compared our method to compression experimental data on a three-particle system. Our study involves quantitative analyses of volume, displacement, and rotational motions. Our results underscore the significance of particle displacement as a key factor in the breakage process while emphasizing the influence of rotational motion. Moreover, our findings effectively capture distinct stages of breakage and rotational movements.

1. INTRODUCTION

Particle breakage can be seen in various industrial and/or research applications. In breaking systems, particles' pre-breakage and after-breakage behavior can influence the system considerably. To be more specific, the breakage can be seen in geotechnical (H. Y. Li et al., 2020; Z. Wu et al., 2019), ocean engineering (Shen et al., 2023), pharmaceutical (Picart et al., 2022; Xiao et al., 2022), etc. As mentioned, the breakage can happen on different scales. Although particle breakage in some cases is a micro-scale phenomenon, the change in characteristics of each system can lead to macro-scale change. For instance, the change in the shape of a grain in a pack of particles can change the stress distribution in such a system. Moreover, the change in the geometrical properties of a grain can add complexity to the problem due to the new contacts between sub-grains. Hence, understanding the breakage process is vital. Particle breakage has been divided into chipping, splitting, and fragmentation. When particles (i.e., sub-particles) have considerable size differences after breakage, the breakage is named chipping. However, splitting is the way of breakage where sub-particles have the same and/or close size; when a particle turns into several pieces, fragmentation breakage occurs. Comprehensive review on the breakage of granular matters can be found elsewhere (Tahmasebi, 2023).
New Afton Convergence Monitoring and Rehabilitation Planning in the B3 Footprint
Authors: Owre S. , Tilley E. , Kamp C.
Published: August 2024

New Afton's B3 block cave footprint has been in steady state production since 2022. During mining, the production footprint is subject to changing stresses that have been observed to cause squeezing and convergence of the drift profile at drawpoints and extraction drives. This can present challenges to the mining operations in terms of drift stability and accessibility of the footprint for equipment. Robust geotechnical monitoring practices have been developed to address this. Convergence is monitored using periodic visual inspections, LiDAR scanning, and multi-point borehole extensometers. These geotechnical monitoring activities generate data that requires interpretation and review during rehabilitation planning. Geotechnical monitoring data is assessed before, during, and after rehabilitation to understand the effectiveness of rehabilitation activities. This paper discusses two practical examples of New Afton's convergence monitoring and rehabilitation practices in the B3 footprint with the objective of documenting the importance of timely and well-planned rehabilitation in achieving safe and efficient production.

1. INTRODUCTION TO NEW AFTON

The New Afton Mine is a block caving operation, located approximately 10 kilometers outside of Kamloops and 350 kilometers northeast of Vancouver in British Columbia. The copper-gold orebody is situated on the Stk'emlupsemc te Secwépemc territory, within the unceded traditional lands of the Secwépemc nation.

In 2021 and 2022, New Afton completed its first two Block Caves on Lift 1, the West and East Caves, which mined over 24.5 MT and 23.7 MT respectively. Currently, New Afton successfully initiated and is monitoring steady state caving of a third cave (B3) beginning in January 2022 with 8.8 MT (probable tonnes). Production involves milling over 8,000 tonnes per operating day from the B3 cave. Footprint development and drawbell blasting is ongoing at a fourth cave (C-Zone), which comprises 29.5 MT (probable tonnes). These mining areas are shown in Figure 1.
Numerical Simulation of Shallow Conductor-Soil Displacement Characteristics in Deep Water Drilling
Authors: Zhang Minghe , Yang Jin , Wang Haige , Cui Longlian , Liu Qi , Kong Lulin , Sun Ke , Jia Wanting
Published: August 2024

Since the shallow soil is mostly composed of clay with weak cementation, the subsea wellhead is easy to be affected by external loads in the initial stage of installation, and the stability of the subsea wellhead is weak, which is prone to serious accidents such as sinking and tilting of the wellhead, resulting in significant economic losses and threatening the safety of deep-water operations. The traditional p-y curve calculation model cannot well reflect the vibration of the subsea wellhead and the detachment and displacement of shallow soil around the surface conductor. However, the Goodman contact element model in numerical simulation can simulate the discontinuity characteristics of the conductor-soil contact interface. In this paper, the numerical simulation method is used to discuss the vertical displacement characteristics of subsea wellhead under cyclic dynamic load and the displacement characteristics of shallow soil particles in different directions and depths around the surface conductor, and the factors affecting the displacement characteristics of conductor and soil are analyzed by load type, conductor installation depth, conductor diameter, and wellhead height above the mudline. It is important to explore the displacement characteristics of subsea wellheads and shallow soil for the design and stability evaluation of subsea wellheads.

1. INTRODUCTION

The construction of a subsea wellhead is the key to the success of deep-water oil and gas drilling, in which the structure of a subsea wellhead mainly depends on the interaction between the surface conductor near the mudline and the surrounding soil to provide bearing capacity (Zhang et al., 2021).

After the installation of the subsea wellhead, it is dynamically stable under the external load of the marine environment and the upper pipe string, which is reflected in the horizontal and reciprocating movement of the surface conductor near the mudline (Zhang et al. 2023). The surface conductor under the mudline has a repetitive action of detachment and extrusion with the surrounding soil, and the position and mechanical property parameters of the soil have changed significantly. As a result, the soil near the mudline cannot provide enough vertical friction for the surface conductor, and part of the soil separated from the surface conductor surface will enter the gap between the surface conductor and the soil, accumulate at the bottom of the gap and become compacted with the reciprocating movement of the conductor, affecting the stability of the subsea wellhead (Su et al. 2010).
Experimental Study on Wall Stability of Acid-Etched Fractures Carbonate Reservoir
Authors: Zhang X. D. , Zhou Jun , Zhou Zhou
Published: August 2024

It is difficult to maintain the conductivity of acid etched fractures in deep carbonate reservoirs. The instability mechanism of acid etched fractures is analyzed by mineral composition analysis, laser scanning before and after acid etched, and continuous strength measurement. By determining the morphology and mechanical characteristics of the fracture wall, the construction parameters such as acid etched time and displacement can be obtained. The continuous strength of the same parts of the rock samples before and after acid etched was compared, and it was found that the strength of some areas increased after acid etched. The main reason for the increase in strength is that the calcite is dissolved by the acid solution, while the dolomite covering the bottom is exposed, and the dolomite strength is higher than the calcite strength. The compressive strength of the dolomite-containing part of the same rock is about 40∼50MPa higher than that of the calcite part.

1. INTRODUCTION

As a reservoir with abundant oil and gas reserves, carbonate rock has become an important research object of oil and gas exploitation. Carbonate reservoir contains 48% of the world's oil and gas reserves. With the discovery of many deep and ultra-deep carbonate oil and gas fields in Tarim, Ordos Basin and other places, the exploitation of carbonate reservoir has become an important research aspect for increasing oil and gas storage and production in China, and acidizing and fracturing is the main technical means for increasing production of carbonate oil and gas fields.

Acidizing fracturing technology is to press acid into the reservoir and form fracture s under conditions higher than the fracturing pressure of the reservoir. At the same time, acid of different systems can react with calcite, dolomite and other rocks on the wall, and non-uniformly etch the fracture wall to form support bodies of different heights. After the completion of construction, the support bodies can effectively support the fractures and make them not completely closed. Finally, a certain length of fracture with flow diversion ability is formed, so as to achieve a production increase effect.
Injection from Well Experiments in Axisymmetric Triaxial Cells: Example of Hydraulic Fracturing
Authors: Kovalyshen Y. , Dautriat J. , Kiewiet L. , Sarout J. , Maney B. , Kager S. , Penny I.
Published: August 2024

Laboratory experiments involving the injection of fluids through rocks under well-controlled conditions can help better constrain the processes taking place at depth during CO2 geo-sequestration in porous reservoirs, or hydraulic fracturing of tight gas/geothermal reservoirs. This article reports the testing of a new method for injecting a fluid through a cased borehole drilled in a cylindrical rock sample subjected to in-situ stress conditions in a conventional axisymmetric triaxial stress vessel. We use rock samples 1.5 inch in diameter in which a 2-mm wellbore can be drilled along or orthogonal to the sample's axis, which is also the direction of maximum principal compressive stress. The casing is made of 1/16 inch perforated stainless steel tube, cemented with a high-strength epoxy. We report here the results of 3 experiments with samples of American Black granite. Water is injected downhole (at the centre of the sample) through a wellbore drilled along or orthogonal to the sample's axis. In this tight rock, the injection pressure reaches a peak and leads to hydraulic fracturing of the sample in both configurations. In addition to the injection parameters (injection pressure/volume, flow rate), the impact of the injection operation is monitored thanks to 16 to 20 ultrasonic transducers attached to the lateral surface of the cylindrical sample, and operated in both active and passive modes. In the case of a sample with horizontal well we observed high stresses around the well that can be attributed to the relatively small size of the sample. As a result, one should not use this configuration to model fluid injection into rock formations in the field. On the other hand in the tests with a vertical well we observed a low breakdown pressure compared to predictions assuming a homogeneous and infinite elastic medium. We attributed this to the relatively large grain/flaw size compared to the well diameter, and the probable stress heterogeneities associated with the epoxy-sealed sections of the well. Finally, we observed a dependency of the P-wave velocity on the state of confining stresses applied to the sample. We argue that this dependency can be, at least partly, explained by the progressive deformation of the rock/sensor interface, rather than solely by the intrinsic stress dependency of the tested rock (e.g., micro-cracks closure with increasing mean compressive stress). We can also report that combined active and passive ultrasonic monitoring allows for an adequate reconstruction of the spatio-temporal evolution of the micro-seismicity induced by hydraulic fracturing.
Influence of Increasing Mean Stress on Rock Fatigue Fracture Characteristics and Failure Mechanism
Authors: Hou Yanan , Wang Li , Liu Yishan , Wu Guangai , Yin Zhiming , Wang Junyan , Fan Baitao , Peng Yan
Published: August 2024

Pulsating hydraulic fracturing (PHF) is a highly potential fracturing technology. Because it can induce fatigue fracture of rocks and generate complex fracture networks by pumping fracturing fluid in pulse form. Understanding fatigue fracture characteristics and failure mechanism of rocks in PHF is crucial for optimizing fracturing construction parameters. In this paper, a series of fatigue fracture toughness experiments including monotonic loading, constant amplitude with constant mean stress(CACMS) cyclic loading and constant amplitude with increasing mean stress(CAIMS) cyclic loading are conducted, respectively. Moreover, fatigue fracture characteristics under these three cyclic loading forms are compared and analyzed. Furthermore, three-dimensional laser scanning is performed on the samples after fatigue fracture to investigate fatigue failure mechanism. Results show that the fracture toughness under CAIMS cyclic loading and CACMS cyclic loading are lower than that under monotonic loading. The samples subjected to cyclic loading failure dissipate more energy during failure, and the roughness of the rock failure surface is also greater than monotonic loading. The results of this paper help to understand the reasons for the higher efficiency of PHF, and provide guidance for the application of PHF technology.

1. INTRODUCTION

Pulse hydraulic fracturing technology has been proven to be a promising technology (Wang et al., 2015; Ni et al., 2018; Lin et al., 2012). This technique induces fatigue damage to reservoir rock by regulating the pumping of fracturing fluid through pulse pressure or pulse flow rate (Ni et al., 2019). As a result, complex fracture network can be generated through the fatigue failure of reservoir rock (Zang et al., 2013; Xie et al., 2020). According to Hou et al. (2021), reservoir rock is subjected to cyclic load with a constant amplitude and an increasing mean stress (CAIMS) when fracturing fluid is pumped in the form of pulse flow rate. Understanding and optimizing the PHF mechanism requires knowledge of the fatigue failure characteristics of rock under this form of cyclic loading.
A 3D Subspring Network Breakable Voronoi Model for Rock: Laboratory-Scale Behavior
Authors: Potyondy D. O. , Fu W.
Published: August 2024

A micromechanical model based on the distinct element method that employs the Subspring Network contact model with rigid, Breakable, Voronoi-shaped grains (SNBV model) is described. The SNBV model is an excellent model for rock microstructure that reproduces the damage mechanisms (heterogeneity-induced local tension, closure of an initial microcrack fabric, and grain breakage) that occur at the grain scale. The laboratory-scale behavior of the synthetic material is summarized as follows. The material exhibits behavior during direct-tension and triaxial compression tests that matches the behavior of intact compact rock. The material can be calibrated to match all of the standard material properties and characteristic stresses as well as the microstructural behavior (including grain breakage) of intact pink Lac du Bonnet granite. The material properties consist of Young's modulus and Poisson's ratio corresponding with uniaxial compression and Young's modulus corresponding with direct tension, as well as tensile strength, crack-closure stress, crack-initiation stress, secondary crack-initiation stress to mark the onset of grain breakage, crack-damage stress, and compressive strengths up to 4 MPa confinement.

1. INTRODUCTION

Bonded-particle models (BPMs) provide a synthetic material consisting of a packed assembly of rigid grains joined by deformable and breakable cement at grain-grain contacts, and whose mechanical behavior is simulated by the distinct-element method. BPMs are being used for rock mechanics research and application (Potyondy, 2015). A new type of BPM called the Hybrid Lattice/Discrete Element Model (hybrid LDEM — a version of the DEM that employs Rigid Body Spring Network interactions) with grain breakage was proposed by Rasmussen (2022), who obtained excellent laboratory-scale behavior for pseudo-3D models consisting of a 3D Voronoi tessellation in which each Voronoi cell is one element thick. The subspring network contact model in PFC3D (Itasca, 2024) is like the hybrid LDEM model. This contact model is combined with a new grain-breakage scheme to provide the Subspring Network contact model with rigid, Breakable, Voronoi-shaped grains (SNBV model). The SNBV model provides excellent laboratory-scale behavior in fully 3D models of cylindrical specimens. The work described in this paper is part of a larger effort to evaluate the ability of the PFC3D code to model spalling by constructing a calibrated SNBV material and studying its laboratory-scale behavior during direct-tension and triaxial compression tests, and its tunnel-scale behavior during excavation of the Mine-by Experiment test tunnel (Read and Martin, 1991). This paper focuses on the laboratory-scale behavior of the SNBV material — refer to Potyondy et al. (2024) for a comprehensive discussion that includes the tunnel-scale behavior as well as a mechanistic explanation of the spalling process.
Modeling of Thermal-Mechanical Impact on Wellbore Integrity Due to CO2 Injection
Authors: Sun Zhuang , Fager Andrew , Crouse Bernd
Published: August 2024

Wellbore integrity is critical to the long-term security of CO2 geological storage. During CO2 injection, the significant temperature difference between the injected CO2 and formation at depth will stress the near wellbore region, potentially leading to generation of leakage pathways. In this work, we perform a numerical study to investigate the role of CO2 injection temperature and pressure based on a 3D coupled thermal-hydro-mechanical model of the formation-cement-casing system. The study takes advantage of the publically available dataset of the Northern Lights project. We present a multistage finite element model that considers the sequential changes of stress and displacement during each stage of the CO2 injector life, such as drilling, casing, cementing, completion, and injection. We simulate a cyclic thermal loading and the results show that no debonding occurs at cement-casing or cement-formation interface during cooling and heating phases, which indicates that the high in-situ effective horizontal stresses tend to mitigate the negative impacts of thermal stresses on wellbore integrity. We also study the impact of several key factors such as the cement elastic moduli and thermal properties. The numerical model offers a solution to quantify the potential thermal-mechanical impact across the entire lifecycle of CO2 injector.

1. INTRODUCTION

Carbon capture, utilization and storage (CCUS) is a critical technology to remove the massive amount of CO2 from the atmosphere and mitigate global warming (Bachu, 2008; Benson & Cole, 2008; Pacala & Socolow, 2004). It will be virtually impossible to achieve net zero goals without CCUS (IEA, 2020). The storage aspect of CCUS involves the injection of CO2 into subsurface saline aquifers or depleted oil and gas reservoirs through wellbores. However, one challenge of CO2 storage is that injected CO2 may find leakage pathways out of the storage reservoir, which adversely affects the surrounding ecosystem and may ultimately re-emerge into the atmosphere (Bachu & Bennion, 2009; Rutqvist et al., 2012; Sun et al., 2023, 2022). It is crucial to prevent leakage from wellbores to establish long-term CO2 storage (Bachu & Watson, 2009; Wigand et al., 2009).
Numerical Analysis of Slope Stability in Open Pit Mining Based on an Integrated Geology and Geomechanics Approach
Authors: Sun Z. , Balasubramanian G. R. , Fager A. , Crouse B. , Barlow G. , Abouaali M.
Published: August 2024

The slope stability analysis usually requires consideration of both geological and geomechanical factors. However, due to the limitation in geological model, current slope stability analysis is typically based upon simplified geological frameworks and does not integrate the key geological complexities required to accurately model the geomechanical response to slope excavation. This study presents an integrated geology and geomechanics approach that can readily assess the geomechanical risk of open pit mining while preserving the geology's integrity. The geological model adopts an implicit modeling of radial basis functions to represent the geology generated from mining survey and borehole drill samples. The 3D geomechanical model is based on a non-linear quasi-static finite element method and the mesh is generated directly from the underlying geological framework. The geomechanics simulation adopts the strength reduction method to evaluate the factor of safety (FOS). The baseline simulation results show a FOS of 1.94, which indicates no shear failure on the open pit mine slope. We also investigate the impact of rock mass geomechanical parameters. The proposed workflow permits us to combine a reliable geological representation with a state-of-the-art rock mechanics finite element solver, which can be used to yield a high fidelity slope stability analysis.

1. INTRODUCTION

Open pit mining refers to mining directly on the ground surface and is a critical mining type around the globe. Slope failures of an open pit mine may lead to catastrophic consequences such as economic losses and fatalities. As the mining depths of open pits continue to increase with the decrease in shallow mineral resources, slope stability analysis is becoming more and more important (Du et al., 2022; Zhang et al., 2022). Slope stability analysis is one of the most classical areas in geotechnical engineering (Christian et al., 1994; Duncan et al., 2014; Sjöberg, 1996). In spite of the slope analysis using conventional techniques, open-pit mines are still experiencing slope failures, which indicates the need to develop better models which improve the prediction and understanding of slope behavior (Kolapo et al., 2022).
Analysis of Rockfall Risk Using Image Analysis and Data-Driven Models
Authors: Ghahramanieisalou M. , Sattarvand J. , Abbasi B. , Peik B. , Battulwar R.
Published: August 2024

The challenge of rockfall and its associated risks has been haunting the mining industry for quite some time. It has been a significant cause of fatalities, serious injuries, and financial losses. Taking advantage of recent technological developments, novel methods of studying rockfalls are introduced. Such renovations are mainly focused on automating geological mapping of the rock surface and data-driven trajectory estimation. UAV photogrammetry and LiDAR were used to gather point cloud data to build a 3D model of the rock slope and extract its geological features. Furthermore, a trajectory estimation model of rockfalls, also developed at UNR's Mining Automation lab, uses the mass and origin of rockfalls to calculate the impact characteristics and simulate a rockfall's energy changes during its fall. Both these developments rely on a combination of physics-based and data-driven models, necessitating continuous data flow. A lab-scale study will further examine the impact of projectile shape and volume on the coefficients of restitution. Building upon the existing correlation's initial results, a data-driven model for trajectory estimation of rockfalls will be developed.

1. INTRODUCTION

Rockfall is the continuous movement of a rock down a steep slope instigated by adverse discontinuity orientation, freeze-thaw cycles, inefficient blasting, water presence, weathering, and vegetation on the slope. The rockfall movement is categorized into free-falling, bouncing, rolling, or sliding (Kliche, 2018).

The rockfall hazard rating system (RHRS), introduced by the US Department of Transportation, is a uniform method to acquire the geographic locations of rockfall sites and categorize them using a two-phase process including three preliminary groups and a detailed classification to identify the most hazardous sites (Kliche, 2018).

However, the general problem with these empirical procedures is their resource-exhaustive approach that requires a very experienced expert to yield the appropriate results. Hence, there is a need for a faster, state-of-the-art, and economical method to deliver reproducible results regardless of the raters' experience.

The geotechnical digital twin (DT) will be a hub for a high-fidelity 3D model, an automated geological mapping algorithm of the rock discontinuities based on point cloud data, and a realistic 3D trajectory simulator for rockfalls, all combined to present the most holistic overview of the rockfall study and analyses.
Comparison of European (EN) and American (ASTM) Abrasion Resistance Test Standards on Some Igneous and Carbonate Origin Natural Stones Subjected to Foot Traffic
Authors: Buyuksagis I. S. , Cakir A. , Gursoy M. , Rostami J.
Published: August 2024

This study compared the results of European Union (EN) and American (ASTM) standards, which are used to determine the abrasion resistance of rocks subjected to foot traffic. The amount of abrasion that will occur due to the friction of pedestrians, especially in the floor covering areas of natural stones, is a crucial criterion in estimating the life of natural stones and deciding whether to use them. In this paper, the correlations between the results obtained by applying EN 14157 and ASTM C241 Abrasion Resistance Determination (ARD) standard test methods on some igneous and carbonate origin stones (limestone, marble, travertine) were determined. Moreover, statistical relationships between some rock properties and abrasion resistance values were investigated. In conclusion, highly reliable correlated inverse relationships were found between the two standard test methods. Statistically highly reliable equations have been proposed to convert a result from the ASTM or EN standard abrasion test method to the outcome of the reciprocal standard test method. The result of single-multiple linear regression analyses, statistically significant regression models with high prediction accuracies were derived (p-values < 0.05; R2 ═ 0.79). In this way, unnecessary time and cost losses for unnecessary sample preparation and testing will be prevented for researchers, and it will help professionals and final users make quicker and more accurate decisions when choosing natural stone for flooring.

1. INTRODUCTION

The appearance of natural stones, currently used in areas inside and outside buildings where pedestrian traffic is heavy in the natural stone industry, deteriorates due to wear and tear caused by friction (Fig. 1), and their repair or replacement causes a significant loss of time and money. To prevent such situations, the European Union (EN) and the American (ASTM) standard test methods are available to predict the amount of wear of natural stones due to friction. These standard methods (EN14157-ASTM C241) are entirely different from each other, and it is impossible to compare or convert the results obtained with each other. According to the results obtained, instead of natural stones with low wear resistance, use those with high wear resistance in places where friction is higher due to pedestrian and goods traffic, such as floors, stairs, thresholds, pavements, etc.