bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicting Excavation Performance of EPB TBM by Using Soil Properties: A Case Study of Dudullu Bostanci Metro Project
Authors: Seyedrezaei M. , Tumac D.
Published: August 2024

This study was conducted to determine the effects of soil properties on the excavation performance of an earth pressure balance tunnel boring machine (EPB TBM) used in the Istanbul Dudullu-Bostanci Tunnel Project. Soil samples were collected from different locations along the tunnel route, and subjected to laboratory tests to determine the particle size distribution, natural water content, consistency limits (liquid limit, plastic limit, plasticity index, and consistency index), fall cone penetration depth, unified soil classification, and clogging potential. The field performance data were obtained from the EPB TBM data logger. Data analysis was carried out by statistically linking the TBM thrust force, and instantaneous cutting rate, with the geotechnical properties of the excavated soil by using single and linear regression methods. The results indicate that the fall cone penetration depth can be used for predicting the thrust force, the plastic limit for the instantaneous cutting rate, and the plastic limit and plasticity index, as well as the consistency index, for field-specific energy predictions. Additional studies are required to provide more reliable and generalized prediction models, by increasing the number of laboratory and field tests for different soil types and performance data for different EPB TBMs.

1. INTRODUCTION

The escalating growth of the urban population has necessitated the development of new infrastructural systems, including metro and water tunnels, along with utility networks. The challenge of optimizing the limited space available, coupled with the need for an infrastructure of higher quality, compels policymakers to consider the more extensive utilization of underground spaces. This scenario requires engineers to devise innovative solutions to tackle the construction challenges encountered in densely populated areas.

The efficacy of management is often subject to examination due to the contractual conflicts that arise in the construction phase. Frequently, the roots of these problems can be identified in the early planning stages. Expectations that are not grounded in realism regarding performance can significantly hinder a contractor's capacity to oversee construction projects with efficiency. Predicting the excavation rate is paramount in the planning of TBM (Tunnel Boring Machine) excavation.

The excavation process typically represents the critical path for tunnel projects, with the project's cost and schedule heavily reliant on the TBM performing as anticipated.
Investigation of Failure Mode and Permeability Evolution of Inclined Heterolithic Strata Using Coupled Discrete Element Method-Computational Fluid Dynamics Model
Authors: Yin X. H. , Zhang B.
Published: August 2024

The presence of inclined heterolithic stratification (IHS) poses significant challenges in operational efficiency for in-situ recovery of oil sands as low-permeability IHS will hinder the vertical propagation of steam chamber. The potential shear failure and slip along IHS may lead to severe instability issues for pit slopes. Coupled Discrete Element Method (DEM)-Computational Fluid Dynamics (CFD) model is constructed to match the flow and geomechanical response of reconstituted IHS specimen and extended to investigate the mechanical behavior, permeability evolution, and failure mode of IHS specimens considering the variation of mud content (0-100%). A novel permeability equation based on porosity variation and crack numbers is established to quantify the permeability change due to macroscopic deformation and failure from a microscopic perspective. This study establishes a quantitative relationship between the geological characteristics and coupled flow-geomechanical behavior of IHS, which is crucial for operational optimization and safe management of in-situ recovery and open-pit mining of oil sands. The developed model is also a useful instrument enabling quantification of mechanical constitutive behavior and permeability evolutions for rock and soil with interbedded weak beddings.

1. INTRODUCTION

The subsurface heterogeneities formed during geological deposition and diagenesis is outstanding challenges in accurate and reliable geotechnical assessment and have attracted increasing attention in subsurface energy geotechnics (Fang & Harrison, 2002; Iferobia & Ahmad, 2020). Weak beddings are the most common types of lithological heterogeneity, which could be traces of fractures or sedimentary structures during the sedimentary processes. As a special form of weak beddings, the existence of IHS in the McMurray Formation of Alberta oil sands leads to pronounced declines in operational efficiency for in-situ recovery of oil sands since it hinders the vertical development of steam chamber (Martinius et al., 2017). A comprehensive investigation of the failure modes and permeability evolution of IHS under stress changes becomes imperative for enhancing recovery efficiency while ensuring the caprock integrity in the in-situ recovery of oil sands. This study aims to investigate the mechanical behavior, permeability evolution, and failure mode of IHS under stress and strain changes.
Investigation on the Spatial Variation in Fracture Orientation and its Impact on Hydraulic Behavior of Rock Mass
Authors: Choi J. , Kim J. , Song J.-J.
Published: August 2024

The consideration of spatial variation in fracture distribution within a rock mass is crucial for enhancing the reliability of Discrete Fracture Network (DFN) modeling because, in nature, fracture properties exhibit non-uniformly distributed characteristics. Few studies have explored the degree of spatial variation within rock masses and its relationship with hydraulic performance. This study investigates the spatial variation of fracture orientation using outcrop data collected from various regions. Twenty-one trace maps were divided into several sub-domains, and the spatial variation between them was analyzed using a correlation coefficient. We find that trace maps exhibit spatial variation in fracture orientation. The degree of variation significantly depends on the region from which the outcrop data originates. It is less influenced by the scale of outcrop maps or the quantity of fractures within the maps. Furthermore, hydraulic analysis was conducted for two trace maps exhibiting high and low spatial variation. The results reveal that high spatial variation leads to larger discrepancies in directional permeability. These findings emphasize the importance of considering spatial variation in fracture orientation when assessing hydraulic behavior in rock masses for application problems.

1. INTRODUCTION

Fracture networks are essential when evaluating the hydraulic behavior of rock masses since fluid flow mainly occurs through fractures rather than rock matrix (Min et al., 2004). Discrete Fracture Network (DFN) modeling, based on statistical characteristics derived from outcrop data, is commonly employed to investigate the permeability of rock masses (Davy et al., 2018).

Numerous studies have analyzed the hydraulic performance of rock masses using DFN (Min et al., 2004; Baghbanan and Jing, 2007; Youn and Gutierrez, 2011). Monte Carlo simulations have been utilized to assign fracture properties for generating DFN models, followed by permeability calculations for various model sizes. The concept of the equivalent discrete fracture network (E-DFN) has been also explored to propose a method for generating DFN with low computational cost (Ren et al., 2017; Ma et al., 2020).

Recently, the spatial distribution characteristics of fractures have emerged as an important consideration. Fracture distribution in real rock masses often exhibits spatial variation or spatial correlation due to factors such as deformation zones or changes in stress regimes (Selroos et al., 2022). These features should be taken into account when modeling DFN for sites that require high precision such as nuclear waste repositories, yet existing methods cannot reflect these characteristics.
Numerical Simulation of Damage Evolution and Fracture Propagation in Deep Shale by Liquid Nitrogen
Authors: Liu Xu , Liu Ying , Qu Hai , Zeng Zhijun , Lu Zhitian , Wang Shi , Liu Xiaodong
Published: August 2024

With abundant deep shale gas resources in China, the future increase in natural gas production is critical. Liquid nitrogen fracturing in deep shale formations can generate complex fractures, making it vital to understand the intricate coupling relationships among the mechanical, flow, and temperature fields within these reservoirs. This paper systematically investigates the mechanisms of damage and fracturing in deep shale under the low-temperature effects of liquid nitrogen, focusing on the characteristics of fracture expansion. Employing a thermo-hydro-mechanical coupling model, the study explores the influence of in-situ stress conditions, borehole length, and bedding angle on the damage evolution of the rock mass in the vicinity of the wellbore. By constructing realistic reservoir models, the research simulates the initiation and expansion of fractures in rock formations under the combined effects of high pressure and thermal stress. It examines the correlation between nitrogen injection duration, fracture density, reservoir temperature, and the laws governing crack initiation and propagation, unveiling the characteristics of fracture damage in deep shale under various parameters and their impact on the morphology of fracture expansion.

1. INTRODUCTION

In recent years, the depletion of conventional oil and gas reservoirs has prompted the oil and gas industry to pivot its focus towards unconventional reservoirs(Bentley, 2002; Kontorovich, Epov, & Eder, 2014). Among these, shale gas has emerged as the fastest-growing source, alongside coalbed methane, tight gas, and natural gas hydrates (Vidic, Brantley, Vandenbossche, Yoxtheimer, & Abad, 2013; Q. Wang, Chen, Jha, & Rogers, 2014). As a crucial element of unconventional oil and gas resources, shale gas has been instrumental in addressing the escalating global demand for fossil fuels.

Hydraulic fracturing, a widely utilized method for economically exploiting shale gas, facilitates the creation of artificial fractures with adequate permeability. Nevertheless, in recent years, traditional large-scale hydraulic fracturing has been increasingly scrutinized due to concerns such as water consumption, environmental pollution, and formation damage(Zou et al., 2017). Furthermore, the adverse impacts of geological variations on fracturing production have ultimately led to a significant reduction in the recovery rate of shale gas wells(Zhao et al., 2023).
Geotechnical Hazards in Deep Mines: Case Studies of Seismicity and Boundaries Changes
Authors: Masethe R. T. , Leite A. R. S. , Landry D.
Published: August 2024

Seismic events and rockbursts are recurrent geotechnical hazards in deep underground mines with significant levels of stress and extraction. These hazards can be manageable if adequately addressed during the design and monitoring phase. However, changes in the geological boundaries can trigger a series of seismic events. Temperature fluctuations and the presence of water can alter the stress conditions, mechanical properties of rock mass and affect geological discontinuities. Two case studies are presented. The first case study focuses on seismicity induced by an underground fire in a deep-level gold mine in South Africa. The second case study investigates seismic events caused by water from backfill pouring in a deep-level copper/nickel mine in Canada. An analysis of the source mechanisms of these induced seismic events revealed that they vary from burst-type to slip-type seismic events. The significant seismic activity during sand fill pouring in the Canadian mine confirmed the high stress predicted by the numerical model (Deviatory Stress Ratio > 0.5). The stress and past seismic events influenced ground support selection for rock burst-prone areas.

1. INTRODUCTION

As mines deepen, geotechnical hazards become less forgiving, and companies must recognize that failing to identify and mitigate these in design and operational strategies could be catastrophic, resulting in significant mine underperformance or premature closure. The objective of these case studies, both in the gold and the copper/nickel mines, is to improve our understanding of the way the fluctuating temperature impacts the operations, and the presence of water can alter the stress conditions, mineralogy, and mechanical properties and affect the geological discontinuities in the deep mines.

The geotechnical hazard results in rockbursts, which are more common in deep, hard rock mines and represent one of the most severe mining hazards affecting the operation's safety, economics, and productivity. The violent and unpredictable nature of these rockbursts makes them remarkably challenging to mitigate and control. The two studies presented below include a case study on seismicity induced by an underground fire in a deep-level gold mine in South Africa. The other case study investigates seismic events caused by water from backfill pouring in a deep-level copper/nickel mine in Canada.
Statistical Analysis of Rock Cutting Forces Acquired from Full-Scale Linear Rock Cutting Machine Tests
Authors: Ishaq Muhammad , Thyagarajan Muthu Vinayak , Rostami Jamal
Published: August 2024

Understanding rock-cutting forces encountered in the field requires full-scale rock-cutting tests with original tools. The most reliable method that accounts for critical aspects of rock-cutting technologies is a full-scale linear cutting machine (LCM) test. The cutting force data acquired through this test sheds light on how the rock and cutter interact, as well as how different cutting geometries and tool variations perform in different geologic formations. Peaks in recorded forces during the full-scale cutting represent the points of a major failure of rock leading to chip formation. This study utilizes a statistical approach to conduct a thorough analysis of cutting force data collected during full-scale LCM testing. As an alternative to the calculation of average or peak cutting force values, the emphasis is on establishing a statistically derived range of forces to assess the cutting force data for performance prediction. The proposed methods and existing methods along with literature were used to model selected machines and compared with field data for validation.

1. INTRODUCTION

A full-scale linear cutting machine (LCM) test is the most reliable method for the evaluation of rock cutting parameters, as it uses large-scale rock samples that closely represent the rock mass character and force requirements in the field (Cho et al., 2013; Dogruoz et al., 2016; Rostami, 1997; Thyagarajan, 2018; Yasar & Yilmaz, 2018). While full-scale LCM tests provide the most realistic rock cutting data, real-world simulation techniques that cannot be combined with other testing methodologies, such as advanced numerical modeling, can be examined (Jeong et al., 2020). The emphasis on full-scale testing arises from the fact that rock is a heterogeneous media with micro/macrostructures, and its behavior is greatly affected by scale (Balci & Bilgin, 2007; Bilgin et al., 2006; Thuro & Plinninger, 2001). Thus, the full-scale LCM test remains the preferred methodology for understanding real-world rock cutting efficiency despite formidable logistical challenges (Balci & Bilgin, 2007; Bilgin et al., 2006; Pan et al., 2018; Rostami, 1997).
Confinement Effect on Operating Limits of TBM Based on a Theoretical Model for Rock Indentation
Authors: Yang Hongwei , Liu Wenjie
Published: August 2024

Mechanized tunneling using tunnel boring machine is mainly a thrust controlled process that can conveniently be modeled by indentation tests. Under confinement, the indentation force required to fragment rocks is significantly larger than that at ambient conditions, which necessitates consideration of lateral confinement in predicting penetration rate. Yet, most of the proposed methods for estimating penetration rate are of phenomenological nature, with only a few based on theoretical analysis for which it is not straightforward to extend to confinement conditions. In this study, we exploited the model recently developed for analyzing data of rock indentation tests with lateral confinement on specimens of variable sizes and extended it to predict penetration rate and thrust required to fragment rocks. The effect of confinement on indentation is accounted for by the increases in compressive strength with lateral confinement. In comparison to CSM model, the model predictions require three extra parameters: confinement, the simplified cavity shape that relates to the cutter shape and the ratio between damage zone size and cutter spacing. The three parameters can be obtained/calibrated by using experimental data obtained from laboratory-controlled linear cutting tests. The predicted operating limits using power of TBM head suggests that under confinement conditions the maximum feasible penetration rate that can be reached is reduced. The proposed method can serve as a start-point for estimating operating limits for TBM under confinement conditions.

1. INTRODUCTION

In mechanized tunneling using tunnel boring machine (TBM) the thrust and penetration rate that can be achieved, or operating limits, are of great interest for the planning and construction stages for a project. Tunneling normally takes place around tens to hundreds meter in depth, thus subjected to elevated in-situ stresses at a magnitude of up to tens of megapascals. Rock behavior at confinement conditions differs from that at ambient conditions according to conventional triaxial compression test results (e.g., Paterson & Wong, 2005), which is also reflected in in the significantly larger thrust required to fragment rocks in rock cutting/indentation tests (e.g., Wang et al., 2021; Wang et al., 2022; Yin et al., 2014). Therefore, predictions of the operating limits would need to include the expected strengthening effect of confinement on rock excavation.
Study on Numerical Simulation Method of Profile Control with Polymer Microspheres
Authors: Ma Mengqi , Li Junjian , Zhu Zhouyuan , Yuan Shuai , Yu Fuwei , Su Hang
Published: August 2024

As a novel method of profile control and enhanced oil recovery, polymer microspheres have been applied extensively in the oil industry. Based on the mechanism of microspheres, an equivalent numerical simulation method is established in the paper to predict its application performance. The method comprehensively considers the properties of microspheres such as expansion, retention, blockage, and degradation. And its accuracy is proven by matching the vital data of laboratory experiments. Then the sensitivity analysis of injection parameters is carried out to optimize simulation results. The reservoirs with different permeability values are selected as cases to predict and evaluate the application effect of the microspheres flooding. It is found that the simulated oil production is consistent with the field data, and there is a significant downward trend in water cut. This numerical simulation method of polymer microspheres is verified by both comparing with experimental data and matching field history, which can be used to guide the reservoir engineering schemes design for microspheres displacement.

1. INTRODUCTION

According to the exploration data of developed oil fields, the reservoirs that can be exploited with sufficient natural energy account for a low proportion of exploitable reservoirs. The waterflooding measure is applied in most oil fields to achieve the goals of maintaining stable production and gaining higher recovery. Nevertheless, because of the increased heterogeneity of the formation, there is still a large amount of crude oil that has not been produced after waterflooding. Therefore, how to relieve the heterogeneity becomes a significant problem for the effective development of such reservoirs (Xie et al, 2023; Wang et al, 2021).

In order to alleviate the above problems and better produce the residual oil in the formation, profile control measures should be adopted. The key to obtaining a great effect by profile control methods lies in selecting the adapted plugging agents. Currently, the commonly used plugging agents are divided into gel, particle, foam and microorganism (Sun et al, 2023; Wang et al, 2020). Among them, the polymer microspheres, which belong to particle-type plugging agents, have attracted wide attention and conducted relevant research because of their characteristics that "being capable of injection, blockage, and movement" (Wu et al, 2022).
Pressure and Stress Prediction Using Seismic Velocities, 3D Geomechanical Models and the Full Stress Tensor: Mad Dog Field, Deepwater GoM
Authors: Nikolinakou M. A. , Flemings P. B. , Heidari M. , Wang X. , Johri M.
Published: August 2024

We discuss a 3D case study for pressure and stress prediction in the Mad Dog field, deepwater GoM. We employ a novel approach that couples seismic velocities with geomechanical models and the full stress tensor (including lateral and deviatoric stresses; FES workflow). We show that steeply inclined salt faces increase the stress ratio in wall rocks. We further show that below salt overhangs, the stress state remains practically uniaxial. We discuss that the approach predicts stress perturbations that result from the 3D salt geometry and extend km away from salt. We extract pressure and stress along a well and show that the geomechanical prediction of least principal stress is systematically lower than the uniaxial estimate but comparable to field measurements. This is because the 3D model captures the extensional effect of the anticline structure in the area. Overall, we demonstrate that the 3D FES models incorporate the complexity of salt loading not captured by any VES approach and can provide pressure and stress estimates along any existing or planned well paths.

1. INTRODUCTION

Pre-drill pore pressure and stress prediction is crucial for borehole stability, planning of safe and economic well trajectories and design of casing plans (Dodson, 2004; Flemings, 2021; Zhang, 2013). It is also a key input in the exploration stage to determine the integrity of reservoir seals.

Pressure-prediction workflows are commonly based on the vertical effective stress (Zhang, 2013). Such workflows have been successfully established because, in sedimentary basins, strain is uniaxial and sedimentation drives loading and overpressure generation (Bowers, 1995; Osborne & Swarbrick, 1997).

In the vertical effective stress (VES) workflow, the vertical effective stress across the volume of interest in calculated by coupling the seismic velocity with a velocity – vertical effective stress relationship, for example that of Bowers (1995):

(equation)

where (equation) is the vertical effective stress, V is a velocity measurement (e.g., seismic or sonic), V0 the velocity of water, and A & B empirical coefficients calibrated using well measurements at a regional well (see Appendix A for nomenclature).

Pore pressure, uVES, is then estimated as the difference between the vertical total stress (σv) and vertical effective stress:

(equation)

The vertical total stress is usually assumed to be equal to the overburden stress.
Quantifying Non-API Proppant Transport and Fracture Permeability as a Function of Solids Loading and Particle Shape
Authors: Leonardi C. R. , Laniewski-Wollk L. , Di Vaira N. J.
Published: August 2024

The use of non-API proppant in hydraulic fracturing has the potential to significantly reduce the cost of hydraulic fracturing operations. However, the influence of particle angularity on proppant transport in rough fractures is not well understood. This work utilises direct numerical simulation (DNS) to quantify changes in fracture permeability as a function of proppant aspect ratio, solid volume fraction, and fracture width. High-fidelity simulations of proppant transport through realistically-textured fractures were conducted using an established numerical framework based on the lattice Boltzmann method and discrete element methods. Particle angularity was captured via clumps of overlapping spheres and the fracture surfaces were described by a power spectral density. The results show that fracture permeability, which is a proxy for injection pressure, smoothly decreases with increasing proppant concentration for all proppant and fracture characterisations. No distinct screen-out was observed, irrespective of particle shape, which contradicts the prevailing assumption that screen-out instantaneously occurs at some threshold of proppant concentration and fracture width. Interestingly, the change in fracture permeability with particle angularity was found to be non-monotonic (decreasing, then increasing, and then decreasing again). It is hypothesized that increases in permeability are a result of the preferential alignment of particles with the flow streamlines. This requires further investigation, along with the analysis of more complex clump shapes such as triangles and tetrahedra. The developed permeability-concentration curves clearly show the influence of particle angularity on injection pressure and can be used to help inform operational decision making when non-API proppant is proposed in reservoir stimulation.

1 INTRODUCTION

The American Petroleum Institute (API) defines criteria for the classification and quality control testing of sand used in hydraulic fracturing. These metrics include sieve analysis for size distribution, sphericity and roundness (minimum > 0.6), acid solubility, turbidity, and crush resistance. The imperative to reduce well completion costs has led to the exploration and deployment of lower-cost products which do not meet one or more of the API criteria. In some limited scenarios, the properties of non-API proppant are deliberately sought (e.g. the use of angular, non-spherical particles to increase pack stability in the fracture due to locking, thereby reducing flow-back to the well). An important consideration associated with the use of non-API proppant is the effect on stimulation efficacy and estimated ultimate recovery (EUR).
Simulating Cyclic Hydraulic Injection-Induced Fatigue with an Improved Discrete Element Method Model
Authors: Xia Chang , Zhao Qi
Published: August 2024

Cyclic hydraulic fracturing (CHF) is currently used for subsurface energy extraction. However, a numerical model that can reproduce the hydraulic fatigue damage is not yet available. In this study, we have developed a fully coupled hydro-mechanical damage model using the Discrete Element Method (DEM). This model incorporates a novel time-dependent failure model to simulate the hydraulic fatigue response. Additionally, we employed the Grain-Based Model (GBM) to simulate heterogeneous incipient cracks, which permit fluid flow after breakage. We numerically calculated the hydraulic injection induced fatigue under varying levels of fluid pressure. These calculations have been validated by laboratory results, demonstrating a reasonable consistency in breakdown pressures. We have thoroughly investigated the effects of CHF on fracture network propagation, providing potential guidance for practical subsurface energy exploitation.

1. INTRODUCTION

Hydraulic stimulation has been widely employed to create a permeable reservoir for subsurface energy extraction since the 1940s (Lecampion et al. 2018; Zimmermann et al. 2019). This process involves injecting pressurized fluids into reservoirs, leading to the formation of complex fracture networks composed of newly developed fractures and reactivated existing ones (Li et al. 2022). However, this stimulation treatment can trigger seismic events, potentially causing earthquakes and leading to public disapproval (Grigoli et al. 2017).

Breakdown pressure, a crucial parameter in hydraulic stimulation, is influenced by rock properties, field stress, and fluid pressure (Xi et al. 2021). The breakdown pressure is generally high due to large field stress and fracture toughness. Consequently, the large pressures and injection fluid volumes have resulted in significant safety concerns (Ellsworth 2013). The goal of stimulation is to devise an advanced injection scheme that can control hydraulic fracturing propagation while simultaneously reducing unwanted seismic events (Majer et al. 2007). In this regard, numerous efforts have been made to develop effective stimulation strategies. Cyclic Hydraulic Fracturing (CHF) is one such strategy aimed at optimizing the development of fracture networks while minimizing environmental impact (Hofmann et al. 2018; Yoon et al. 2015; Zang et al. 2013). In contrast to conventional hydraulic fracturing, which adopts continuous injection, CHF employs periodic high- and low-injection pressures (Zhuang et al. 2019). The fluid-rock interaction within the incipient fracture tips can cause hydraulic fatigue, thus making it possible to adopt a lower breakdown pressure to reduce seismic risks (Rao and Ramana 1992; Zhuang et al. 2019). In addition, the permeability of rock is enhanced during CHF compared to conventional hydraulic fracturing (Zimmermann et al. 2019).
Measurement of Crack Tip Opening Displacement and Strain Fields Using Global Digital Image Correlation (DIC)
Authors: Bhandari Tushar , Deb Debasis
Published: August 2024

The assessment of fracture properties such as crack tip opening displacement (CTOD), plastic zone size, and crack development is essential for understanding the behavior of cracks and fractures in geological materials. Crack displacement requires full-field strain measurement as the strain field develops in front of the propagating crack. The point-based strain measurement devices, such as strain gauge and extensometers, fails to capture crack growth. This study proposes a Finite Element based Digital Image Correlation (FE-DIC) method for measuring fracturing process especially, crack tip displacement and associated strain localization. The paper outlines the FE-DIC algorithm and its validation with numerical images and laboratory testing. The numerical images are created using Irwin's near-crack tip displacement approximation function around a center crack in an infinite plate under equibixial tension (Irwin, 1957). In the laboratory, the Mode I three-point bending fracture test is performed on a cuboidal slab of sandstone and basalt rock with a center notch. The results show that the FE-DIC method can capture the non-linear displacement field as the crack propagates and also estimate plastic zone around the crack. The findings of this study provide evidence supporting the efficacy of the global FE-DIC method in visualizing strains and fracture propagation.

1 INTRODUCTION

The study of the rock fracturing process is crucial for designing various geotechnical projects such as mines, dams, reservoir, underground nuclear waste disposal, and tunnels (Guo et al., 2023; Xing et al., 2022). Most rocks exhibit strain-softening to brittle behavior and fail without any prior indication. To understand the failure mechanism of rocks due to fracture propagation, the insight of full field deformation under various loading conditions is a necessity. Critical challenges in characterizing the crack-induced rock failure includes locating the crack, estimating its propagation path and identifying the strain localization zone in the crack tip where the stress-strain relationship is non-linear, which acts as the precursor of the macroscopic crack extension known as Fracture Process Zone (FPZ) (Qiao et al., 2023). These challenges are more prominent while dealing with brittle materials like rock, which fails at low strain and thus demands a robust fullfield deformation measurement method.
Incorporating Roughness Degradation Within the Critical State Framework: Modeling the Shear Behavior of Rock Joints
Authors: Matsuoka Yuki , Kikumoto Mamoru , Ogata Sho , Kishida Kiyoshi
Published: August 2024

Rock masses are characterized by numerous structural discontinuities, such as joints and faults, which exert a significant influence on their deformation responses. Therefore, it is important to develop a constitutive model that can accurately anticipate the mechanical response of rock joints. A previous study proposed an elastoplastic constitutive model based on the critical state framework originally developed in soil mechanics. The fundamental assumption of this model is that a rock joint reaches a critical state, where the shear stress and aperture is uniquely determined relative to the applied normal stress, after a large shear displacement. This model accounts for the joint matching by evaluating the difference in joint aperture between the current and the critical state. However, its applicability to rock joints remains incomplete, particularly in accommodating the influence of roughness degradation. Roughness degradation on joint surfaces can lead to a reduction in the asperity angle, resulting in a decrease in aperture at the critical state and a dilatancy response. In this study, we extend the aforementioned model by introducing a state parameter to account for the changes in critical state aperture. The proposed model effectively captures alterations in the shear response associated with the roughness degradation, providing a more comprehensive understanding of the mechanical behavior of rock joints.

1. INTRODUCTION

The precise anticipation of rock mass behavior is critical in designing and maintaining rock structures such as tunnels, dam foundations, geological repositories for radioactive waste, and energy storage facilities. Within the rock mass, numerous discontinuities, such as faults and joints, characterized by reduced stiffness and strength compared to the rock materials, exert a significant influence on the overall rock mass behavior. In addition, alterations in stress conditions within the rock mass resulting from subsurface activities can induce slippage of these discontinuities, precipitating the failure or collapse of the entire rock mass. Therefore, comprehending and managing the slip behavior of discontinuities, particularly those surrounding underground structures, represents one of the critical challenges in rock engineering.

Although various studies have explored slip/shear behavior, the surface roughness (Barton, 1973) and interlocking (Zhao, 1997a) of rock joints are important factors influencing shear behavior under applied stress conditions common in rock engineering. Numerous numerical methodologies have been proposed to forecast the behavior of discontinuities in rock. Nevertheless, enhancing constitutive models to incorporate geological characteristics of in-situ joints remain imperative.
Dual-Target Predictive Intelligence Model for Predicting D90 Particle Size and Total Concentration of Lost Circulation Materials
Authors: Shang Guanyi , Yang Heng , Feng Yongcun , Li Xiaorong
Published: August 2024

Lost circulation events occur frequently during the drilling process. Due to their sudden and difficult to predict nature, they are often difficult to control in the field, resulting in low success rates and increased costs. Therefore, accurate formulation of lost circulation materials (LCMs) is essential for effective lost circulation management. However, the current lack of clear guidelines for LCM formulation in the field introduces uncertainty and subjectivity. Traditional machine learning methods struggle with the diversity of LCM types and combinations, making direct formulation recommendations difficult. In particular, the D90 size of the primary bridging particles and the total concentration of LCMs are essential for successful control of lost circulation. This study presents a dual-target deep learning model designed to predict these critical parameters, thereby aiding in the precise formulation and optimization of LCMs. By selecting eleven key features as model inputs, the model can understand complex relationships within the data by exploiting connections between layers and weighting adjustments. Test results show high accuracy and robustness, with R2 values of 0.91 for D90 particle size and 0.83 for material concentration, providing valuable guidance for LCM development and optimization.

1. INTRODUCTION

Lost circulation, a frequent and unpredictable challenge in drilling, significantly impacts oil industry operations. This phenomenon, where drilling fluids are lost into formations through well walls, leads to various drilling issues like well control problems, hole instability, and production inefficiencies, ultimately resulting in increased nonproductive time and costs (Feng & Gray, 2017). The complexity and unpredictability of geological conditions exacerbate these challenges, highlighting the need for effective management strategies.

Lost circulation materials (LCMs) are the basis for successful loss control (Zhang et al.,2016). The effectiveness of the LCMs depends on its suitability for the loss conditions and drilling fluid type (Zhou et al.,2022). The characteristics of lost circulation determine the key performance of LCMs (Xu et al., 2022). Central to their function is the adjustment of particle size within the drilling mud to effectively seal pores and fractures addressable by mud alone (White, 1956). Optimal particle size and distribution are vital; overly small particles fail to bridge gaps, while excessively large ones cannot penetrate cracks, underscoring the importance of precise selection for efficient and effective sealing.
Experimental Study on CO2 Fracturing of Continental Shale with Dense Laminas
Authors: Zhang Xiaohuan , Zhang Shicheng , Zou Yushi , Ma Xinfang , Xiong Dong , Liu Li , Yang Peng , Zhu Danyang
Published: August 2024

Using CO2 to increase shale oil production is a practical requirement to ensure energy security and reduce carbon emissions. Therefore, studying the fracture propagation mechanics of CO2 fracturing is of great significance. This article applies a triaxial fracturing simulation system combined with a CO2 control system to perform supercritical CO2 (SC-CO2) fracturing, CO2 aqueous solution (CO2 aqs) fracturing, slick water fracturing, and gel fracturing on continental shale. The results indicate that CO2 fracturing has the effect of reducing breakdown pressure, and the breakdown pressure of supercritical CO2 fracturing and CO2 aqs pre-immersion fracturing is lower than that of slick water fracturing. The artificial fractures induced by low-viscosity slick water fracturing in shale with dense laminas are easily inhibited by the laminas, and it is difficult to propagate in the direction of fracture height. The ultra-low viscosity and strong diffusivity of SC-CO2 lead to multiple laminas and micro-fractures being activated, and the main fracture is not obvious. The main fracture width of CO2 aqs pre-immersion fracturing is relatively large, the fracture propagation path is tortuous, and multiple laminas are activated. The complexity of the fracture induced by CO2 aqs solution is 75% higher than that induced by slick water. The effect of CO2-water-rock interaction on fracture propagation cannot be ignored. In addition, there is a significant positive correlation between the complexity coefficient of fractures and acoustic emission shear activity ratio.

1. INTRODUCTION

The success of the United States in the efficient development of marine shale oil has sparked a wave of exploration and development of unconventional oil and gas resources worldwide (Zou et al. 2020). Under the tectonic background of the foreland basin, the Jurassic in the Sichuan Basin of China is located in a sedimentary environment of deep to semi-deep lakes, forming a large and stable set of dark shale interbedded with carbonate or siltstone formations, laying an important material foundation for the formation and enrichment of shale oil (He et al. 2022). However, the strong heterogeneity, complex lithology, and dense laminas of continental shale pose challenges for fracturing development (Guo et. 2023). To improve the effect of reservoir stimulation, CO2 fracturing technology was explored and applied in the oilfield (Li et al. 2020). CO2 as a fracturing fluid can effectively reduce formation damage and increase formation pressure, and help reduce greenhouse gas emissions (Li et al. 2022). Therefore, studying the fracture propagation mechanics of CO2 fracturing is of great significance.
Reservoir Fine Evaluation of Horizontal Well Multi-Stage Fracturing Based on Unsupervised Cluster Machine Learning
Authors: Wang W. C. , Ma X. F. , Zou Y. S. , Zhang S. C. , Liu L. , Yang P. , Zhao Z. W. , Zheng A. , Wang X. , Yang L. F.
Published: August 2024

The accuracy of comprehensive evaluation is low, the effect of multi-stage and multi-cluster design is poor, and it is difficult to ensure the maximum stimulation efficiency. The comprehensive quality of reservoirs is quantitatively evaluated by considering the physical properties and fracability of reservoirs based on logging data. This evaluation integrated reservoir quality (RQ) and completion quality (CQ) from a geology-engineering perspective, a model is established using the entropy weight method (EWM) and the analytic hierarchy process (AHP). Then, the unsupervised Gaussian Mixture Model (GMM) clustering is applied to categorize the composite quality index (CQI), resulting in the development of a novel evaluation model for multi-cluster fractured. The evaluation and clustering are conducted using Jimusaer shale oil well A in Xinjiang and Ordos Basin well B in Qingcheng as case studies. Upon comparing the results with the actual oil production, it is discovered that: the comprehensive quality can be quantitatively characterized by the evaluation model; the GMM can accurately identify good fracability zones, and the coincidence rate with the results of the oil production is as high as 83.3%, which confirms the accuracy of the proposed method, provides a good technical foundation for optimizing the location of multi-stages and multi-clusters.

1. INTRODUCTION

Under the current background of unconventional oil and gas exploitation with low quality aiming at cost reduction and efficiency improvement, an important step to carry out multi-stage and cluster stimulation for low and ultralow permeability reservoirs is to determine good reservoir quality (RQ) and completion quality (CQ) (Hu et al., 2018). Usually, there are problems such as parameter diversification and inaccurate quantification in quality evaluation (Lei et al., 2019; Lei et al., 2022), and unreasonable position of multi-stage and perforation cluster, resulting in low production after reservoir stimulation (Miller et al., 2011; Wigger et al., 2014).
A Study of the Collapse of Fractured Sandstone Strata Characterized by High In-Situ Stress Differences in Deep Formations
Authors: Xu Zehao , Zhang Wen , Liu Xiangjun , Liang Lixi , Jing Yadong
Published: August 2024

Under the condition of high in-situ stress differences, the issue of wellbore instability in fractured sandstone formations is prominent. Through rock mechanics experiments combined with the theory of weak planes, a quantitative study on the mechanical characteristics of fractured sandstone and the collapsing area around the wellbore was conducted. The results indicate that the matrix strength of tight sandstone is high, but the presence of fractures increases the likelihood of failure in fractured sandstone, resulting in a reduction of its overall strength to 14% of the matrix strength. Under vertical well conditions, compared to uniform horizontal in-situ stress conditions, the risk of fracture instability caused by high horizontal stress differences increases. However, when the fracture orientation aligns with the direction of maximum principal stress, the risk of fracture instability is the lowest. When formations develop fractures with low to moderate dip angles, drilling in the direction of maximum horizontal stress can lead to a larger collapse area for wells with moderate inclinations; if drilling in the direction of minimum principal stress, the maximum collapse area decreases as the fracture angle increases. The study results have certain guidance significance for the safe and efficient development of deep oil and gas resources.

1. INTRODUCTION

The deepest oil and gas wells today have reached depths of up to 9000 meters. The successful exploitation of ultra-deep oil and gas resources critically depends on advancements in petroleum engineering and rock mechanics (Xie et al., 2021). However, the geological conditions of deep formations are complex, and the three high characteristics (high temperature, high pressure, and high H2S content) of formations lead to prominent wellbore instability issues (Han et al., 2021). For instance, due to the influence of natural fractures, the safe drilling density window is narrow, and situations where wellbore collapse and leakage coexist may occur. Therefore, wellbore instability in fractured sandstone formations under high in-situ stress differences is one of the key scientific issues that deep drilling engineering needs to consider.
Pore Pressure Prediction in Deep Complex Formations Based on Well-Seismic Combination
Authors: Yang Zixuan , Ye Chenxi , Wang Qian , Zhai Wenbao , Tan Peng , Chen Zhaowei
Published: August 2024

With the development of oil and gas drilling technology, oil and gas exploration and development have moved towards deep to ultra-deep layers. Due to its deep burial depth, deep formations face various challenges such as high temperature, high pressure, and high stress. The prediction of formation pore pressure is a core factor of drilling design optimization and risk prevention. In order to improve the prediction accuracy on the basis of existing pre-drilling formation pore pressure prediction methods, the logging data and actual drilling data of the drilled wells were combined with the seismic data. In this paper, a set of high accuracy pore pressure prediction method based on well-seismic combination are formed by using the interval-controlled interval velocity modeling method and the well-controlled interval velocity correction method. The method is applied to a deep well in Tarim Basin. This well was designed to exceed a depth of 8,000 meters. The predicted pore pressure coefficient of the well is between 1.04 and 1.22 g/cm3. The measured pore pressure coefficient after drilling was between 1.07 and 1.22 g/cm3. Actual analysis has demonstrated the accuracy and reliability of pore pressure prediction, providing support for pre-drilling pressure forecasts.

1. INTRODUCTION

In recent years, with the acceleration of China's exploration and development of deep oil and gas resources, the demand for ultra-deep well drilling technology has become increasingly urgent, and higher requirements have been put forward for ultra-deep well drilling technology. However, the engineering geological conditions of ultra-deep formations are extremely complex, and the design of wellbore structures under multiple pressure systems is difficult, which also poses great challenges to efficient and safe drilling. Therefore, for ultra-deep and complex formations, solving the problem of accurate prediction of formation pore pressure under complex geological conditions has great practical significance for oil and gas drilling. At the same time, it also provides strong technical support for the exploration and development of ultra-deep oil and gas resources.