A Cohesive Model for Modeling Hydraulic Fractures in Naturally Fractured Formations

2015 ◽  
Author(s):  
M.. Gonzalez ◽  
A. Dahi Taleghani ◽  
J. E. Olson
Keyword(s):  
Fracture Mechanics ◽  
Failure Modes ◽  
Cohesive Zone Model ◽  
Void Nucleation ◽  
Natural Fracture ◽  
Model Parameters ◽  
Hydraulic Fractures ◽  
Zone Model ◽  
Fluid Viscosity ◽  
Naturally Fractured

Abstract A cohesive zone model (CZM) has been developed to couple fluid flow with elastic, plastic and damage behavior of rock during hydraulic fracturing in naturally fractured formations. In addition to inelastic deformations, this model incorporates rock anisotropies. Fracture mechanics of microcrack and micro-void nucleation and their coalescence are incorporated into the formulation of the CZM models to accurately capture different failure modes of rocks. The performance of the developed elastoplastic and CZM models are compared with the available data of a shale play, and then the models are introduced into a commercial finite element package through user-defined subroutines. A workflow to derive the required model parameters for both intact rock and cemented natural fractures is presented through inverse modeling of field data. The hydraulic fractures' growth in the reservoir scale is then simulated, in which the effect of fluid viscosity, natural fracture characteristics and differential stresses on induced fracture network is studied. The simulation results are compared with the available solutions in the literature. The developed CZM model outperforms the traditional fracture mechanics approaches by removing stress singularities at the fracture tips, and simulation of progressive fractures without any essential need for remeshing. This model would provide a robust tool for modeling hydraulic fracture growth using conventional elements of FEA.

scholarly journals Using Cohesive Zone Model to Simulate the Hydraulic Fracture Interaction with Natural Fracture in Poro-Viscoelastic Formation

Energies ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1254 ◽  
Author(s):  
Yu Suo ◽  
Zhixi Chen ◽  
Hao Yan ◽  
Daobing Wang ◽  
Yun Zhang
Keyword(s):  
Numerical Model ◽  
Pore Pressure ◽  
Hydraulic Fracture ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Fracture Propagation ◽  
Natural Fracture ◽  
Zone Model ◽  
Fluid Viscosity ◽  
Fluid Diffusion

Hydraulic fracturing is a widely used production stimulation technology for conventional and unconventional reservoirs. The cohesive element is used to explain the tip fracture process. In this paper, the cohesive zone model was used to simulate hydraulic fracture initiation and propagation at the same time rock deformation and fluid exchange. A numerical model for fracture propagation in poro-viscoelastic formation is considered. In this numerical model, we incorporate the pore-pressure effect by coupling fluid diffusion with shale matrix viscoelasticity. The numerical procedure for hydraulically driven fracture propagation uses a poro-viscoelasticity theory to describe the fluid diffusion and matrix creep in the solid skeleton, in conjunction with pore-pressure cohesive zone model and ABAQUS was used as a platform for the numerical simulation. The simulation results are compared with the available solutions in the literature. The higher the approaching angle, the higher the differential stress, tensile stress difference, injection rate, and injection fluid viscosity, and it will be easier for hydraulic fracture crossing natural fracture. These results could provide theoretical guidance for predicting the generation of fracture network and gain a better understanding of deformational behavior of shale when fracturing.

Poroelastoplastic Modeling of Complex Hydraulic-Fracture Development in Deep Shale Formations

SPE Journal ◽  
2021 ◽  
pp. 1-25
Author(s):  
Wenzheng Liu ◽  
Qingdong Zeng ◽  
Jun Yao
Keyword(s):  
Adverse Effect ◽  
Hydraulic Fracture ◽  
Cohesive Zone Model ◽  
Picard Iteration ◽  
Natural Fracture ◽  
Rock Properties ◽  
Hydraulic Fractures ◽  
Zone Model ◽  
Shale Formations ◽  
Fracture Development

Summary In this paper, we propose a hydromechanical model to simulate hydraulic fracture propagation in deep shale formations. The Drucker-Prager plasticity theory, Darcy’s law, Reynolds lubrication theory, and Kirchoff’s laws are adopted to describe the plastic deformation, matrix flow, fracture flow, and wellbore flow, respectively. A global embedded cohesive zone model is constructed to achieve the free evolution of hydraulic fractures and the characterization of natural fractures. The finite element method (FEM) and finite volume method (FVM) are used for the spatial discretization of the stress field and pressure field. On the basis of Newton-Raphson iteration, fixed-stress iteration, and Picard iteration, a mixed numerical scheme is built up to solve the strong nonlinear coupling problem. The proposed model is verified against several reference cases and experimental results. Finally, some numerical cases are carried out to investigate the influences of rock properties, natural fracture distribution, and fracturing fluid properties on the complex hydraulic fracture development. The results show that rock plasticity leads to a decrease in stimulated fracture area, an increase in average fracture width, and an increase in propagation pressure. As the cluster number increases, the adverse effect of rock plasticity on multiple hydraulic fracturing in deep shale formations increases significantly. In addition, appropriate optimization of cluster spacing could weaken the adverse effect of rock plasticity on fracturing treatment to a certain extent by using the stress interference effect.

Effects of asphalt concrete characteristics on cohesive zone model parameters of hot mix asphalt mixtures

2016 ◽  
Vol 43 (3) ◽  
pp. 226-232 ◽  
Author(s):  
S. Pirmohammad ◽  
H. Khoramishad ◽  
M.R. Ayatollahi
Keyword(s):  
Asphalt Concrete ◽  
Cohesive Energy ◽  
Cohesive Zone ◽  
Hot Mix Asphalt ◽  
Cohesive Zone Model ◽  
Experimental Tests ◽  
Model Parameters ◽  
Zone Model ◽  
Binder Type ◽  
Air Void

In this paper, the effects of the main asphalt concrete characteristics including the binder type and the air void percentage on the cohesive zone model (CZM) parameters were studied. Experimental tests were conducted on semi-circular bend (SCB) specimens made of asphalt concrete and the fracture behavior was simulated using a proper CZM. The CZM parameters of various hot mix asphalt (HMA) mixtures were determined using the SCB experimental results. Five types of HMA mixtures were tested and modeled to consider the effects of binder type and air void percentage on the CZM parameters. The results showed that as the binder in HMA mixture softened, the cohesive energy strength increased, whereas enhancing the air void percentage led to reduction of the cohesive energy and strength values. Among the studied HMA mixtures, the highest values of CZM parameters were found for the HMA mixture containing a copolymer called styrene-butadiene-styrene.

Analytical and Machine-LearningAnalysis of Hydraulic Fracture-Induced Natural Fracture Slip

SPE Journal ◽  
2021 ◽  
pp. 1-17
Author(s):  
Peidong Zhao ◽  
K. E. Gray
Keyword(s):  
Failure Modes ◽  
Statistical Significance ◽  
Frictional Coefficient ◽  
Natural Fracture ◽  
Hydraulic Fractures ◽  
Well Performance ◽  
Stimulated Reservoir Volume ◽  
Relative Angle ◽  
Statistical Measures ◽  
Net Pressure

Summary Stimulated reservoir volume (SRV) is a prime factor controlling well performance in unconventional shale plays. In general, SRV describes the extent of connected conductive fracture networks within the formation. Being a pre-existing weak interface, natural fractures (NFs) are the preferred failure paths. Therefore, the interaction of hydraulic fractures (HFs) and NFs is fundamental to fracture growth in a formation. Field observations of induced fracture systems have suggested complex failure zones occurring in the vicinity of HFs, which makes characterizing the SRV a significant challenge. Thus, this work uses a broad range of subsurface conditions to investigate the near-tip processes and to rank their influences on HF-NF interaction. In this study, a 2D analytical workflow is presented that delineates the potential slip zone (PSZ) induced by a HF. The explicit description of failure modes in the near-tip region explains possible mechanisms of fracture complexity observed in the field. The parametric analysis shows varying influences of HF-NF relative angle, stress state, net pressure, frictional coefficient, and HF length to the NF slip. This work analytically proves that an NF at a 30 ± 5° relative angle to an HF has the highest potential to be reactivated, which dominantly depends on the frictional coefficient of the interface. The spatial extension of the PSZ normal to the HF converges as the fracture propagates away and exhibits asymmetry depending on the relative angle. Then a machine-learning (ML) model [random forest (RF) regression] is built to replicate the physics-based model and statistically investigate parametric influences on NF slips. The ML model finds statistical significance of the predicting features in the order of relative angle between HF and NF, fracture gradient, frictional coefficient of the NF, overpressure index, stress differential, formation depth, and net pressure. The ML result is compared with sensitivity analysis and provides a new perspective on HF-NF interaction using statistical measures. The importance of formation depth on HF-NF interaction is stressed in both the physics-based and data-driven models, thus providing insight for field development of stacked resource plays. The proposed concept of PSZ can be used to measure and compare the intensity of HF-NF interactions at various geological settings.

Effects of adhesive thickness on the mode I cohesive zone model parameters of a high toughness structural adhesive

2018 ◽  
Author(s):  
M. H. R. de Oliveira ◽  
A. F. Ávila ◽  
R. R. Chaves ◽  
H. Nascimento Júnior ◽  
F. D. Passos
Keyword(s):  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Model Parameters ◽  
Mode I ◽  
Zone Model ◽  
High Toughness ◽  
Adhesive Thickness ◽  
Structural Adhesive

Multiscale Model to Study the Effect of Interfaces in Carbon Nanotube-Based Composites

2005 ◽  
Vol 127 (2) ◽  
pp. 222-232 ◽  
Author(s):  
S. Namilae ◽  
N. Chandra
Keyword(s):  
Carbon Nanotubes ◽  
Molecular Dynamics ◽  
Finite Element ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Interfacial Region ◽  
Model Parameters ◽  
Zone Model ◽  
Pullout Tests ◽  
Nanoscale Interfaces

In order to fully harness the outstanding mechanical properties of carbon nanotubes (CNT) as fiber reinforcements, it is essential to understand the nature of load transfer in the fiber matrix interfacial region of CNT-based composites. With controlled experimentation on nanoscale interfaces far off, molecular dynamics (MD) is evolving as the primary method to model these systems and processes. While MD is capable of simulating atomistic behavior in a deterministic manner, the extremely small length and time scales modeled by MD necessitate multiscale approaches. To study the atomic scale interface effects on composite behavior, we herein develop a hierarchical multiscale methodology linking molecular dynamics and the finite element method through atomically informed cohesive zone model parameters to represent interfaces. Motivated by the successful application of pullout tests in conventional composites, we simulate fiber pullout tests of carbon nanotubes in a given matrix using MD. The results of the pullout simulations are then used to evaluate cohesive zone model parameters. These cohesive zone models (CZM) are then used in a finite element setting to study the macroscopic mechanical response of the composites. Thus, the method suggested explicitly accounts for the behavior of nanoscale interfaces existing between the matrix and CNT. The developed methodology is used to study the effect of interface strength on stiffness of the CNT-based composite.

Revisiting the Problem of Debond Initiation at Fibre-Matrix Interface under Transversal Biaxial Loads - A Comparison of Several Non-Classical Fracture Mechanics Approaches

2016 ◽  
Vol 713 ◽  
pp. 232-235 ◽  
Author(s):  
L. Távara ◽  
I.G. García ◽  
Roman Vodička ◽  
C.G. Panagiotopoulos ◽  
Vladislav Mantič
Keyword(s):  
Fracture Mechanics ◽  
Cohesive Zone Model ◽  
Failure Criteria ◽  
Transverse Load ◽  
Zone Model ◽  
Interface Model ◽  
Matrix Interface ◽  
Linear Elastic ◽  
Energetic Approach ◽  
Fibre Matrix

Understanding matrix failure in LFRP composites is one of the main challenges when developing failure criteria for these materials. This work aims to study the influence of the secondary transverse load on the crack initiation at micro-scale. Four non-classical approaches of fracture mechanics are used to model the onset of fibre-matrix interface debonds: Linear Elastic Brittle Interface Model (LEBIM), an Energetic Approach for the Linear Elastic Brittle Interface Model (EA-LEBIM), an Energetic Approach for the bilinear Cohesive Zone Model (EA-CZM) and the Coupled Criterion of the Finite Fracture Mechanics (CC-FFM). Results obtained by these approaches predict that, for brittle fibre-matrix configurations, a secondary transverse compression reduces the critical value of the main transverse tension leading to the debond onset. This fact is not taken into account by the currently used failure criteria

scholarly journals Application of a Cohesive Zone Model for Simulating Fatigue Crack Growth from Moderate to High ΔK Levels of Inconel 718

2018 ◽  
Vol 2018 ◽  
pp. 1-13
Author(s):  
Huan Li ◽  
Jinshan Li ◽  
Huang Yuan
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Small Scale ◽  
Model Parameters ◽  
Zone Model ◽  
Crack Growth Rates

A cyclic cohesive zone model is applied to characterize the fatigue crack growth behavior of a IN718 superalloy which is frequently used in aerospace components. In order to improve the limitation of fracture mechanics-based models, besides the predictions of the moderate fatigue crack growth rates at the Paris’ regime and the high fatigue crack growth rates at the high stress intensity factor ΔK levels, the present work is also aimed at simulating the material damage uniformly and examining the influence of the cohesive model parameters on fatigue crack growth systematically. The gradual loss of the stress-bearing ability of the material is considered through the degradation of a novel cohesive envelope. The experimental data of cracked specimens are used to validate the simulation result. Based on the reasonable estimation for the model parameters, the fatigue crack growth from moderate to high ΔK levels can be reproduced under the small-scale yielding condition, which is in fair agreement with the experimental results.

scholarly journals Crash Analysis of Aluminum/CFRP Hybrid Adhesive Joint Parts Using Adhesive Modeling Technique Based on the Fracture Mechanics

Polymers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 3364
Author(s):  
Young Cheol Kim ◽  
Soon Ho Yoon ◽  
Geunsu Joo ◽  
Hong-Kyu Jang ◽  
Ji-Hoon Kim ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Composite Laminates ◽  
Cohesive Zone Model ◽  
Failure Behavior ◽  
Zone Model ◽  
Displacement Curve ◽  
Adhesive Failure ◽  
Aluminum Composite ◽  
Explicit Finite Element ◽  
Modeling Techniques

This study describes the numerical simulation results of aluminum/carbon-fiber-reinforced plastic (CFRP) hybrid joint parts using the explicit finite-element solver LS-DYNA, with a focus on capturing the failure behavior of composite laminates as well as the adhesive capacity of the aluminum–composite interface. In this study, two types of adhesive modeling techniques were investigated: a tiebreak contact condition and a cohesive zone model. Adhesive modeling techniques have been adopted as a widely commercialized model of structural adhesives to simulate adhesive failure based on fracture mechanics. CFRP was studied with numerical simulations utilizing LS-DYNA MAT54 to analyze the crash capability of aluminum/CFRP. To evaluate the simulation model, the results were compared with the force–displacement curve from numerical analysis and experimental results. A parametric study was conducted to evaluate the effect of different fracture toughness values used by designers to predict crash capability and adhesive failure of aluminum/CFRP parts.

Experimental and numerical analysis of dual-adhesive stepped-lap aluminum joints

2020 ◽  
Vol 234 (5) ◽  
pp. 454-464
Author(s):  
CL Ferreira ◽  
RDSG Campilho ◽  
RDF Moreira
Keyword(s):  
Cohesive Zone ◽  
Failure Modes ◽  
Cohesive Zone Model ◽  
Stress Gradient ◽  
Maximum Load ◽  
Lap Joints ◽  
Adhesive Joints ◽  
Zone Model ◽  
Behavior Prediction ◽  
Adhesive Bonds

The use of adhesive bonds has attracted considerable interest from the scientific community. Stepped-lap joints have the advantage of decreasing stress gradients along the bond length, although the outer steps still encounter stress levels above the steps in the inner zone of the joint. One possible way to reduce this stress gradient is to combine this type of joint with the use of two adhesives. This work consists of an experimental and numerical evaluation of stepped-lap dual-adhesive joints between aluminum adherends, for various overlap lengths ( LO), and comparison with stepped-lap single-adhesive joints. The adhesives Araldite® AV138, Araldite® 2015, and Sikaforce® 7752 were evaluated. Numerically, cohesive zone models with a triangular damage law were applied in the joint behavior prediction. The analysis of the results is presented in the form of failure modes, stress analysis, damage variable analysis, load–displacement ( P–δ) curves and maximum load ( Pm), and energy required to failure ( U). It was concluded that, in general, cohesive zone model presented precise predictions. In general, no significant increase in strength was achieved with dual-adhesive joint but, on the other hand, significant energy increases were obtained.

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