Numerical Investigation Of Interaction Between Hydraulic Fractures And Natural Fractures
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Numerical Investigation Of Interaction Between Hydraulic Fractures And Natural Fractures
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Author : Wenxu Xue
language : en
Publisher:
Release Date : 2011
Numerical Investigation Of Interaction Between Hydraulic Fractures And Natural Fractures written by Wenxu Xue and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
Hydraulic fracturing of a naturally-fractured reservoir is a challenge for industry, as fractures can have complex growth patterns when propagating in systems of natural fractures in the reservoir. Fracture propagation near a natural fracture (NF) considering interaction between a hydraulic fracture (HF) and a pre-existing NF, has been investigated comprehensively using a two dimensional Displacement Discontinuity Method (DDM) Model in this thesis. The rock is first considered as an elastic impermeable medium (with no leakoff), and then the effects of pore pressure change as a result of leakoff of fracturing fluid are considered. A uniform pressure fluid model and a Newtonian fluid flow model are used to calculate the fluid flow, fluid pressure and width distribution along the fracture. Joint elements are implemented to describe different NF contact modes (stick, slip, and open mode). The structural criterion is used for predicting the direction and mode of fracture propagation. The numerical model was used to first examine the mechanical response of the NF to predict potential reactivation of the NF and the resultant probable location for fracture re-initiation. Results demonstrate that: 1) Before the HF reaches a NF, the possibility of fracture re-initiation across the NF and with an offset is enhanced when the NF has weaker interfaces; 2) During the stage of fluid infiltration along the NF, a maximum tensile stress peak can be generated at the end of the opening zone along the NF ahead of the fluid front; 3) Poroelastic effects, arising from fluid diffusion into the rock deformation can induce closure and compressive stress at the center of the NF ahead of the HF tip before HF arrival. Upon coalescence when fluid flows along the NF, the poroelastic effects tend to reduce the value of the HF aperture and this decreases the tension peak and the possibility of fracture re-initiation with time. Next, HF trajectories near a NF were examined prior to coalesce with the NF using different joint, rock and fluid properties. Our analysis shows that: 1) Hydraulic fracture trajectories near a NF may bend and deviate from the direction of the maximum horizontal stress when using a joint model that includes initial joint deformation; 2) Hydraulic fractures propagating with higher injection rate or fracturing fluid of higher viscosity propagate longer distance when turning to the direction of maximum horizontal stress; 3) Fracture trajectories are less dependent on injection rate or fluid viscosity when using a joint model that includes initial joint deformation; whereas, they are more dominated by injection rate and fluid viscosity when using a joint model that excludes initial joint deformation.
The Effect Of Cemented Natural Fractures On Hydraulic Fracture Propagation
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Author : Weiwei Wang
language : en
Publisher:
Release Date : 2017
The Effect Of Cemented Natural Fractures On Hydraulic Fracture Propagation written by Weiwei Wang and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with categories.
Microseismic events, which are generated during hydraulic fracturing treatments, suggest that a complicated fracture network develops in many naturally−fractured unconventional reservoirs. Deformation along weak planes, such as cemented natural fractures, has been proposed as one of the possible reasons for fracture network complexity. Cemented natural fractures widely exist in shale reservoirs. They are diverse in composition and size, depending on the burial condition, the composition of the rock matrix, and the geochemical environment. The interaction between cemented natural fractures with hydraulic fractures generated as part of the reservoir stimulation are thought to impact hydraulic fracture propagation. Previous studies mostly treated natural fractures as frictional interfaces without considering the actual cement fillings. In this study, I analyzed the effect of cemented natural fractures on hydraulic fracture propagation by considering natural fracture thickness, mechanical properties and rock−cement interface bond strength. Firstly, I conducted a series of semi−circular bend (SCB) tests and corresponding numerical simulations to study the interaction between hydraulic and natural fractures. The SCB tests are attractive in general because of their simple setup with consistent results. The experimental results also served as a validation for numerical model. Two drawbacks of the SCB tests include that the test is unconfined and there is no fluid component. Numerical modeling can then be applied to extend results beyond these shortcomings. Synthetic hydrostone samples with embedded inclusions of different mechanical properties were used to mimic rock with cemented natural fractures. Experimental results identified several parameters that could be used to explain hydraulic fractures interaction with cemented natural fractures. The SCB test conditions that promoted fracture crossing were near−orthogonal approach angles, small natural fracture thicknesses, and strong rock−cement interfaces. Such conditions in a reservoir would promote long hydraulic fractures and less complicated fracture networks. In contrast, the SCB test conditions that caused fracture diverting were more oblique approach angles, large natural fracture thicknesses, and weak rock−cement interfaces, resulting in short hydraulic fractures and more complicated fracture networks. The SCB tests using synthetic rock samples provided insights into the hydraulic fracture propagation in naturally−fractured reservoirs. Through the numerical modeling with the finite element code in Abaqus, the impact of fluid driven fracturing on fracture−fracture interaction was investigated. Fracture propagation in two dimensions was modeled using the cohesive elements and anisotropic compressive remote stress conditions. Results suggest that if the natural fracture thickness is considered, the commonly used fracture crossing/diverting criterion will overestimate the hydraulic fracture crossing scenario. Factors including modulus contrast and coefficient of friction also influence hydraulic fracture interaction with natural fractures. An application of this work is the case of how bedding−parallel veins will affect hydraulic fracture height growth. Such natural fractures are abundant in the unconventional resource play in the Vaca Muerta formation in Argentina. When the rock−cement coefficient of friction is around 0.4−0.5, which most likely represents shale reservoirs, hydraulic fracture crossing behavior is affected by the modulus contrast between natural fractures and host rock as well as the natural fracture thickness.
Geomechanics And Hydraulic Fracturing For Shale Reservoirs
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Author : Yu Wang
language : en
Publisher: Scientific Research Publishing, Inc. USA
Release Date : 2020-07-01
Geomechanics And Hydraulic Fracturing For Shale Reservoirs written by Yu Wang and has been published by Scientific Research Publishing, Inc. USA this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020-07-01 with Art categories.
This book is intended as a reference book for advanced graduate students and research engineers in shale gas development or rock mechanical engineering. Globally, there is widespread interest in exploiting shale gas resources to meet rising energy demands, maintain energy security and stability in supply and reduce dependence on higher carbon sources of energy, namely coal and oil. However, extracting shale gas is a resource intensive process and is dependent on the geological and geomechanical characteristics of the source rocks, making the development of certain formations uneconomic using current technologies. Therefore, evaluation of the physical and mechanical properties of shale, together with technological advancements, is critical in verifying the economic viability of such formation. Accurate geomechanical information about the rock and its variation through the shale is important since stresses along the wellbore can control fracture initiation and frac development. In addition, hydraulic fracturing has been widely employed to enhance the production of oil and gas from underground reservoirs. Hydraulic fracturing is a complex operation in which the fluid is pumped at a high pressure into a selected section of the wellbore. The interaction between the hydraulic fractures and natural fractures is the key to fracturing effectiveness prediction and high gas development. The development and growth of a hydraulic fracture through the natural fracture systems of shale is probably more complex than can be described here, but may be somewhat predictable if the fracture system and the development of stresses can be explained. As a result, comprehensive shale geomechanical experiments, physical modeling experiment and numerical investigations should be conducted to reveal the fracturing mechanical behaviors of shale.
3 D Modeling Of Interaction Between A Hydraulic Fracture And Multiple Natural Fractures Using Finite Element Analysis
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Author : Debashish Talukder
language : en
Publisher:
Release Date : 2019
3 D Modeling Of Interaction Between A Hydraulic Fracture And Multiple Natural Fractures Using Finite Element Analysis written by Debashish Talukder and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019 with Finite element method categories.
A three-layered, 3-D geo-mechanical model was developed using Finite Element Analysis (FEA) software (ABAQUS) to simulate single stage hydraulic fracturing treatment in a synthetic fractured model based on available shale information from literature. The main objectives of this study were- (i) to investigate the interaction between a hydraulic fracture (HF) orthogonally intersecting two parallel natural fractures (NF) and (ii) to identify significant parameters and their 2-factor interactions that affect HF propagation in the presence of multiple NFs. Based on literature review, an initial set of 20 parameters (a combination of geologic and drilling parameters) was selected. Those parameters were believed to affect the hydraulic fracture propagation in a naturally fractured model. Experiments were conducted in two stages. First-order order numerical experiments were conducted under the Plackett-Burman experimental design. Central Composite Design (CCD) was used to check curvature and to take care of non-linearity existing in the dataset. A stepwise sensitivity analysis and parametric study were conducted to identify significant parameters and their interactions. When the HF interacted with NFs, there were three possible outcomes- the HF either got arrested, dilated or crossed the NF. The overall hydraulic fracture geometry depended on the type of interaction behavior occurring at the intersection. The NF leakoff coefficient was the most significant factor in the 1st order experiments that affected the HF propagation in the presence of multiple NFs. CCD results suggested that NF strength at the bottom shale layer and injection fluid viscosity significantly influenced the HF opening in the presence of the natural fractures. The most significant two-factor interaction was the interaction between stress contrast and Young’s modulus of the overburden shale (Ytop). This study will help understand the interaction behavior between a HF and two pre-existing NFs. The parametric study will provide a valuable insight for hydraulic fracturing treatment in a naturally fractured formation.
Imaging The Mechanics Of Hydraulic Fracturing In Naturally Fractured Reservoirs Using Induced Seismicity And Numerical Modeling
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Author : Xueping Zhao
language : en
Publisher:
Release Date : 2010
Imaging The Mechanics Of Hydraulic Fracturing In Naturally Fractured Reservoirs Using Induced Seismicity And Numerical Modeling written by Xueping Zhao and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
Experimental And Numerical Study Of Interaction Of A Pre Existing Natural Interface And An Induced Hydraulic Fracture
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Author : Mohammad Sarmadivaleh
language : en
Publisher:
Release Date : 2012
Experimental And Numerical Study Of Interaction Of A Pre Existing Natural Interface And An Induced Hydraulic Fracture written by Mohammad Sarmadivaleh and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.
Today's huge growth of energy need may not be fulfilled except using new source of unconventional energy that should be stimulated hydraulically. However, these reservoirs are non-homogeneous and contain various types of interfaces which make their fracturing treatment difficult. In this study, the interaction between the hydraulic fracture and a natural interface were investigated using analytical, numerical and experimental approaches. This was done by doing sensitivity analysis on some of the important parameters.
Analysis Of Interaction Between Hydraulic And Natural Fractures
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Author : Jaber Taheri-Shakib
language : en
Publisher:
Release Date : 2016
Analysis Of Interaction Between Hydraulic And Natural Fractures written by Jaber Taheri-Shakib and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with Technology categories.
The behavior of natural fractures at the hydraulic fracturing (HF) treatment is one of the most important considerations in increasing the production from this kind of reservoirs. Therefore, considering the interaction between the natural fractures and hydraulic fractures can have great impact on the analysis and design of fracturing process. Due to the existence of such natural fractures, the perturbation stress regime around the tip of hydraulic fracture leads to some deviation in the propagation of path of hydraulic fracture. Increasing the ratio of transverse stress to the interaction stress results in a reduction in the deviation of hydraulic fracturing propagation trajectory in the vicinity of natural fracture. In this study, we modeled a hydraulic fracture with the extended finite element method (XFEM) using a cohesive-zone technique. The XFEM is used to discrete the equations, allowing for the simulation of induced fracture propagation; no re-meshing of domain is required to model the interaction between hydraulic and natural fractures. XFEM results reveal that the distance and angle of natural fracture with respect to the hydraulic fracture have a direct impact on the magnitude of tensile and shear debonding. The possibility of intersection of natural fracture by the hydraulic fracture will increase with increasing the deviation angle value. At the approaching stage of hydraulic fracture to the natural fracture, hydraulic fracture tip exerts remote compressional and tensile stress on the interface of the natural fracture, which leads to the activation and separation of natural fracture walls.
Hydraulic Fracture Propagation Through Geological Discontinuities
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Author : Ella María Llanos Rodríguez
language : en
Publisher:
Release Date : 2015
Hydraulic Fracture Propagation Through Geological Discontinuities written by Ella María Llanos Rodríguez and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with Hydraulic fracturing categories.
Hydraulic fracturing is a stimulation technique widely used to enhance hydrocarbon production and geothermal energy extraction. Other applications include waste disposal and cave inducement and preconditioning of ore for mining. Rocks are naturally fractured and therefore the little-understood problem of hydraulic fracture growth through these pre-existing discontinuities is a key area of research. Mathematical criteria for predicting whether an induced fracture will cross a discontinuity have been published by several authors. Some used parameters that are difficult to quantify, neglected the stress induced by the hydraulic fracture itself and ignored fluid viscosity effects on crossing behaviour. Others ignored the presence of fluid in the hydraulic fracture, the possibility of fracture re-initiation after slippage and the effect of surface features on crossing. Numerical studies have shown that viscosity-dominated hydraulic fractures would induce slip on the discontinuity more easily than toughness-dominated hydraulic fractures. This implies that crossing should be more difficult for viscosity-dominated hydraulic fractures. To investigate the interaction between hydraulic and natural fractures, laboratory experiments are combined with numerical and analytical work in this thesis to extend two previously published criteria. This thesis shows the effect of viscosity on the crossing interaction is complex and cannot be predicted based only on whether slip occurs on the discontinuity before the hydraulic fracture intersects it. The laboratory work can also be applied to improved understanding of the effect of the stress field on crossing as it relates to hydraulic fracture height growth. Prediction of the effect of weak bedding planes on height growth has recently gained importance as the risk of vertical growth of fractures into aquifers has emerged as a concern in shale gas and coal seam gas operations. The findings herein can be applied to this problem if the frictional interfaces are considered to represent weak bedding planes. Complete treatment of the height growth problem requires considering fracture growth through elastic layers with contrasts in physical properties. The experiments show hydraulic fractures may grow to become elliptical because they extend more quickly and further in the direction of maximum stress or in the direction with fewer discontinuities. The preparation of the samples underlined the effect of local imperfections on discontinuities. Small areas of higher or lower contact stress can aid or inhibit fracture initiation. Rock plates must be smooth and flat in order to control this parameter and obtain valid experimental comparisons for contact stress and the other parameters controlling crossing. Numerical and analytical results are presented as a mathematical expression with universal curves for the locations of slip starting points, providing an important aid for designing industrial hydraulic fractures. One difference between the approach used here and that used by others is their use of the fracture-tip singular stress solution, meaning they do not consider the effect of the non-singular stresses existing around a pressurised fracture. This thesis therefore improves their work. Experimental and theoretical outcomes herein suggest that hydraulic fracture growth through an orthogonal discontinuity does not depend primarily on the interface friction coefficient. This finding contradicts several models.
Simulation Of Hydraulic Fractures And Their Interactions With Natural Fractures
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Author : Varahanaresh Sesetty
language : en
Publisher:
Release Date : 2012
Simulation Of Hydraulic Fractures And Their Interactions With Natural Fractures written by Varahanaresh Sesetty and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.
Modeling the stimulated reservoir volume during hydraulic fracturing is important to geothermal and petroleum reservoir stimulation. The interaction between a hydraulic fracture and pre-existing natural fractures exerts significant control on stimulated volume and fracture network complexity. This thesis presents a boundary element and finite difference based method for modeling this interaction during hydraulic fracturing process. In addition, an improved boundary element model is developed to more accurately calculate the total stimulated reservoir volume. The improved boundary element model incorporates a patch to calculate the tangential stresses on fracture walls accurately, and includes a special crack tip element at the fracture end to capture the correct stress singularity the tips The fracture propagation model couples fluid flow to fracture deformation, and accounts for fracture propagation including the transition of a mechanically-closed natural fractures to a hydraulic fracture. The numerical model is used to analyze a number of stimulation scenarios and to study the resulting hydraulic fracture trajectory, fracture aperture, and pressures as a function of injection time. The injection pressure, fracture aperture profiles shows the complexity of the propagation process and its impact on stimulation design and proppant placement. The injection pressure is observed to decrease initially as hydraulic fracture propagates and then it either increases or decreases depending on the factors such as distance between hydraulic fracture and natural fracture, viscosity of the injected fluid, injection rate and also other factor that are discussed in detail in below sections. Also, the influence of flaws on natural fracture in its opening is modeled. Results shows flaws that are very small in length will not propagate but are influencing the opening of natural fracture. If the flaw is located near to one end tip the other end tip will likely propagate first and vice versa. This behavior is observed due to the stress shadowing effect of flaw on the natural fracture. In addition, sequential and simultaneous injection and propagation of multiple fractures is modeled. Results show that for sequential injection, the pressure needed to initiate the later fractures increases but the geometry of the fractures is less complicated than that obtained from simultaneous injection under the same fracture spacing and injection. It is also observed that when mechanical interaction is present, the fractures in sequential fracturing have a higher width reduction as the later fractures are formed.
Extended Finite Element Method
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Author : Amir R. Khoei
language : en
Publisher: John Wiley & Sons
Release Date : 2015-02-23
Extended Finite Element Method written by Amir R. Khoei and has been published by John Wiley & Sons this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015-02-23 with Science categories.
Introduces the theory and applications of the extended finite element method (XFEM) in the linear and nonlinear problems of continua, structures and geomechanics Explores the concept of partition of unity, various enrichment functions, and fundamentals of XFEM formulation. Covers numerous applications of XFEM including fracture mechanics, large deformation, plasticity, multiphase flow, hydraulic fracturing and contact problems Accompanied by a website hosting source code and examples