June 17, 2021

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Hydraulic Fracture Modeling

Hydraulic Fracture Modeling
Author : Yu-Shu Wu
Publisher : Gulf Professional Publishing
Release Date : 2017-12-12
Category : Technology & Engineering
Total pages :566
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Hydraulic Fracture Modeling delivers all the pertinent technology and solutions in one product to become the go-to source for petroleum and reservoir engineers. Providing tools and approaches, this multi-contributed reference presents current and upcoming developments for modeling rock fracturing including their limitations and problem-solving applications. Fractures are common in oil and gas reservoir formations, and with the ongoing increase in development of unconventional reservoirs, more petroleum engineers today need to know the latest technology surrounding hydraulic fracturing technology such as fracture rock modeling. There is tremendous research in the area but not all located in one place. Covering two types of modeling technologies, various effective fracturing approaches and model applications for fracturing, the book equips today’s petroleum engineer with an all-inclusive product to characterize and optimize today’s more complex reservoirs. Offers understanding of the details surrounding fracturing and fracture modeling technology, including theories and quantitative methods Provides academic and practical perspective from multiple contributors at the forefront of hydraulic fracturing and rock mechanics Provides today’s petroleum engineer with model validation tools backed by real-world case studies

Hydraulic Fracture Modeling in Naturally Fractured Reservoirs

Hydraulic Fracture Modeling in Naturally Fractured Reservoirs
Author : Kaustubh Shrivastava
Publisher : Unknown
Release Date : 2019
Category :
Total pages :239
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Hydraulic fracturing of horizontal wells is one of the key technological breakthroughs that has led to the shale revolution. Hydraulic fracturing models are used to engineer hydraulic fracture design and optimize production. Typically, hydraulic fracturing models treat hydraulic fractures as planar, bi-wing fractures. However, recent core-through investigations have suggested that during hydraulic fracturing in naturally fractured reservoirs, complex hydraulic fracture geometries can be created due to the interaction of the growing hydraulic fracture with natural fractures. This limits the application of planar fracture models for optimizing hydraulic fracturing design in naturally fractured reservoirs. In this research, we present a novel three-dimensional displacement discontinuity method based hydraulic fracturing simulator that allows us to model hydraulic fracture growth in the presence of natural fractures along with proppant transport in an efficient manner. The model developed in this dissertation is used to investigate the interaction of a hydraulic fracture with natural fractures and study the transport of proppant in the resulting complex fracture networks. This investigation gives us novel insight into the influence of fracture geometry and stress interference on the final distribution of proppant in fracture networks. Based on this investigation, suggestions are made to improve proppant transport in complex fracture networks. In order to correctly capture the effect of natural fractures on fracture growth, knowledge about the distribution of natural fractures in the reservoir is imperative. Typically, little is known about the in-situ natural fracture distribution, as direct observation of the reservoir is not possible. A novel technique of synthetic coring is developed to create a discrete fracture network (DFN) from core data, and it is used to create a DFN based on the Hydraulic Fracturing Test Site #1 data. Hydraulic fracture propagation is modeled in the created DFN, and the results are compared with field observations. As the reservoir may contain thousands of natural fractures, simulations in a realistic DFN can be computationally very expensive. In order to reduce the computational requirements of the simulator, we present a novel predictor step based on the local linearization method that provides a better initial guess for solving the fluid-solid interaction problem. This is shown to reduce computational time significantly. A novel technique, Extended Adaptive Integral Method, to speed up the simulator is developed. The method uses an effective medium to represent the interaction between displacement discontinuity elements and reduces the order of complexity of solving the geomechanical system of equations from O(N2) to O(NlogN). The novel formulation of this method is presented, and sensitivity studies are conducted to show the improvement in computational efficiency

Mechanics of Hydraulic Fracturing

Mechanics of Hydraulic Fracturing
Author : Ching H. Yew,Xiaowei Weng
Publisher : Gulf Professional Publishing
Release Date : 2014-09-19
Category : Technology & Engineering
Total pages :234
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Revised to include current components considered for today's unconventional and multi-fracture grids, Mechanics of Hydraulic Fracturing, Second Edition explains one of the most important features for fracture design - the ability to predict the geometry and characteristics of the hydraulically induced fracture. With two-thirds of the world's oil and natural gas reserves committed to unconventional resources, hydraulic fracturing is the best proven well stimulation method to extract these resources from their more remote and complex reservoirs. However, few hydraulic fracture models can properly simulate more complex fractures. Engineers and well designers must understand the underlying mechanics of how fractures are modeled in order to correctly predict and forecast a more advanced fracture network. Updated to accommodate today's fracturing jobs, Mechanics of Hydraulic Fracturing, Second Edition enables the engineer to: Understand complex fracture networks to maximize completion strategies Recognize and compute stress shadow, which can drastically affect fracture network patterns Optimize completions by properly modeling and more accurately predicting for today's hydraulic fracturing completions Discusses the underlying mechanics of creating a fracture from the wellbore Enhanced to include newer modeling components such as stress shadow and interaction of hydraulic fracture with a natural fracture, which aids in more complex fracture networks Updated experimental studies that apply to today's unconventional fracturing cases

Advanced Hydraulic Fracture Modeling

Advanced Hydraulic Fracture Modeling
Author : Jason Robert York
Publisher : Unknown
Release Date : 2018
Category :
Total pages :189
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In the effort to create new technology to enhance our ability to retrieve hydrocarbons, the technique of hydraulic fracturing has shown to be extremely beneficial. This involves pumping fluids at high pressures and high rates to induce and propagate fractures near the wellbore to stimulate production in otherwise low permeability reservoirs. To better understand the physical processes involved, several models have been proposed for numeric simulation. This work expands on an existing hydraulic fracturing model based on the nonlocal theory of peridynamics, detailed in Ouchi et al. [3]. Peridynamics is a relatively new reformulation of continuum mechanics, applicable even when discontinuities such as fractures are introduced. To incorporate the influence of inelasticity in the established model, which may be significant for several geologic materials, a multi-surface yield model is proposed. This yield model builds on a Drucker-Prager related yield model formulated for peridynamics by Lammi et al. [46], adding a tension cut-off surface as well as a cap to include hardening effects associated with inelastic compaction. The formulation of these additional surfaces in the peridynamic framework will be detailed and numerically demonstrated in this dissertation. As the peridynamic based hydraulic fracture model continues to develop complex capabilities, such as inelasticity, computational expense continues to be an ever-growing concern. Although the peridynamic formulation has demonstrated the capability of modeling complex fracture behavior, the computational expense is noted to be quite expensive relative to classic local models. Recently, methods have been introduced for coupling nonlocal bond based peridynamic grids with local finite element meshes, detailed in Galvanetoo et al. [74]. These coupling methods have demonstrated applicability to static equilibrium mechanics problems, while introducing negligible errors. In this work, the coupling method is implemented with the nonlocal hydraulic fracturing model, using peridynamics near existent and propagating fractures, as well as a standard finite element formulation far from the influence of such features. To further increase computational efficiency, a dynamically adaptive mesh coarsened away from the peridynamic region is implemented with the capability of converting finite element nodes to peridynamic nodes. This novel method of coupling peridynamics with a highly efficient mesh in the hydraulic fracture model will be fully detailed in this dissertation. In addition, 2D and 3D results will be provided using this method, demonstrating the capability of the coupled model to simulate complex fracture behavior, as well as discuss its impact on simulation capabilities and performance.

Advances in Hydraulic Fracture Simulation - Dynamic and Quasi-static Analysis

Advances in Hydraulic Fracture Simulation - Dynamic and Quasi-static Analysis
Author : Matin Parchei Esfahani
Publisher : Unknown
Release Date : 2019
Category : Finite element method
Total pages :170
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Hydraulic fracturing (HF) is an effective technique for permeability enhancement of conventional and unconventional reservoirs. HF is performed by injecting a fluid (usually water-based), sand, and chemicals into a formation under high pressure in order to induce damage and improve the interconnectivity of the fracture network through reopening of natural fractures and generation of new fractures. Hydraulic fracturing is a complex multi-physics process that involves the coupling of several physical phenomena, such as rock deformation, fluid flow, fracture propagation, etc. The simulation of HF is complex due to its coupled multi-physics nature. Despite recent advancements in HF simulations, relatively little attention has been given to improving the coupling algorithms used in these simulations. In many cases, sequential coupling algorithms are preferred over the monolithic approach due to the availability of independent solvers for each subproblem (e.g., independent deformable solid and fluid flow models), and the costliness of the monolithic approach. However, the available sequential algorithms widely used in the simulation of hydraulic fractures are known to lack robustness and encounter stability and/or convergence issues. The unavailability of efficient and effective sequential algorithms for the simulation of hydraulic fractures is currently one of the major gaps in the literature. The majority of hydraulic fracture models use quasi-static analysis, which neglects the inertial effects that are important when injection rates are very high or vary quickly in time, as during stimulation by pressure pulsing. The application of the dynamic models currently available in the literature is mainly limited to the dynamic simulations of acoustic wave emissions in porous media. Very few studies, until now, have considered dynamic simulation of fluid driven fractures. Hence, the unavailability of reliable dynamic hydraulic fracture models is another major gap in the hydraulic fracture literature. This thesis has three objectives. The first objective is to develop a stable sequential coupling algorithm for enforcing the hydro-mechanical coupling in the simulation of hydraulic fractures. The focus of the first objective is on the sequential algorithms that solve the mechanics subproblem first, in each iteration. This objective is realized in Chapter 2 of the thesis. The split is derived using the analogy of the undrained split in poromechanics; hence the new algorithm is named the \emph{undrained HF split}. The undrained HF split converges to the solution of the fully coupled (monolithic) approach. It's also shown to be stable and convergent in applications in which the conventional coupling strategies fail to converge due to oscillations. The convergence of the undrained HF split is generally slower than the fully coupled model. The second objective of the thesis is to develop a stable sequential coupling algorithm that solves the fluid flow subproblem first, in each iteration. This objective is addressed in Chapter 3 of the thesis. This algorithm is derived using the analogy of the fixed stress split in poromechanics and, therefore, named the \emph{fixed stress HF split}. The fixed stress HF split is stable and shown to converge to the solution of the fully coupled model. The algorithm is shown to successfully simulate nonplanar hydraulic fracture trajectories in flow rate controlled hydraulic fracture simulations. The third objective of the thesis is to develop a dynamic hydraulic fracture model for investigating the effect of rapidly changing loads, such as those caused by pressure pulses, on the dynamic propagation of hydraulic fractures. Chapter 4 of the thesis addresses this objective. A dynamic HF model with leak-off is developed in Chapter 4. The dynamic HF model is used to study wellbore stimulation by high rate and high amplitude pressure pulses and investigate the effect of formation porosity and permeability on the dynamic response of the system. It is observed that generally, formations with higher porosity and permeability generate shorter and wider hydraulic fractures. The dynamic response of hydraulic fractures is found to contain a phase lag with respect to the applied pressure pulse, which slightly increases with an increase in the porosity and permeability of the formation. Fracture closure mechanism is directly affected by the rate of fluid leak-off from hydraulic fractures, which also depends on the porosity and permeability of the formation. Unique acoustic wave emission patterns are observed from the response of hydraulic fracture and wellbore system to the pressure pulse at each stage of the stimulation.

Hydraulic Fracture Optimization Using Hydraulic Fracture and Reservoir Modeling in the Piceance Basin, Colorado

Hydraulic Fracture Optimization Using Hydraulic Fracture and Reservoir Modeling in the Piceance Basin, Colorado
Author : Harris Allen Reynolds
Publisher : Unknown
Release Date : 2012
Category :
Total pages :342
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Hydraulic fracturing is an important stimulation method for producing unconventional gas reserves. Natural fractures are present in many low-permeability gas environments and often provide important production pathways for natural gas. The production benefit from natural fractures can be immense, but it is difficult to quantify. The Mesaverde Group in the Piceance Basin in Colorado is a gas producing reservoir that has low matrix permeability but is also highly naturally fractured. Wells in the Piceance Basin are hydraulically fractured, so the production enhancements due to natural fracturing and hydraulic fracturing are difficult to decouple. In this thesis, dipole sonic logs were used to quantify geomechanical properties by combining stress equations with critically-stressed faulting theory. The properties derived from this log-based evaluation were used to numerically model hydraulic fracture treatments that had previously been pumped in the basin. The results from these hydraulic fracture models, in addition to the log-derived reservoir properties were used to develop reservoir models. Several methods for simulating the reservoir were compared and evaluated, including layer cake models, geostatistical models, and models simulating the fracture treatment using water injection. The results from the reservoir models were compared to actual production data to quantify the effect of both hydraulic fractures and natural fractures on production. This modeling also provided a framework upon which completion techniques were economically evaluated.

Hydraulic Fracture Modeling with Finite Volumes and Areas

Hydraulic Fracture Modeling with Finite Volumes and Areas
Author : Eric Cushman Bryant
Publisher : Unknown
Release Date : 2016
Category :
Total pages :354
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In Chapter 1, a finite volume-based arbitrary fracture propagation model is used to simulate fracture growth and geomechanical stresses during hydraulic fracture treatments. Single-phase flow, poroelastic displacement, and in situ stress tensor equations are coupled within a poroelastic reservoir domain. Stress analysis is used to identify failure initiation that proceeds by failure along Finite Volume (FV) cell faces in excess of a threshold effective stress. Fracture propagation proceeds by the cohesive zone (CZ) model, to simulate propagation of non-planar fractures in heterogeneous porous media under anisotropic far-field stress. In Chapter 2, we are concerned with stress analysis of both elastic and poroelastic solids on the same domain, using a FV-based numerical discretization. As such our main purposes are twofold: introduce a hydromechanical coupling term into the linear elastic displacement field equation, using the standard model of linearized poroelasticity; and, maintain the continuity of total traction over any multi-material interfaces (meaning an interface over which residual stresses, Biot’s coefficient, Young’s modulus, or Poisson’s ratio vary). In Chapter 3, we are concerned with modeling fluid flow in cracks bounded by deforming rock, and specifically, inside those initial discontinuities, softening regions and failed zones which constitute the solid interfaces of propagating hydraulic fractures. To accomplish this task the Finite Area (FA) method is an ideal candidate, given its proven facility for the discretization and solution of 2D coupled partial differential equations along the boundaries of 3D domains. In Chapter 4, rock formations’ response to a propagating, pressurized hydraulic fracture is examined. In order to initiate CZ applied traction-separation processes, an effective stress tensor is constructed by additively combining the total stress with pore pressures multiplied into a scalar factor. In effect, this scalar factor constitutes the Biot’s coefficient as acts inside the CZ. Integral analysis at the cohesive tip is used to show that this factor must be equal to the Biot’s coefficient in the bounding solid (for a small-strain constitutive relation). Also, effects of an initial residual stress state are accounted for.

Numerical Modeling of Hydraulic Fracture Propagation Using Thermo-hydro-mechanical Analysis with Brittle Damage Model by Finite Element Method

Numerical Modeling of Hydraulic Fracture Propagation Using Thermo-hydro-mechanical Analysis with Brittle Damage Model by Finite Element Method
Author : Kyoung Min
Publisher : Unknown
Release Date : 2013
Category :
Total pages :129
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Better understanding and control of crack growth direction during hydraulic fracturing are essential for enhancing productivity of geothermal and petroleum reservoirs. Structural analysis of fracture propagation and impact on fluid flow is a challenging issue because of the complexity of rock properties and physical aspects of rock failure and fracture growth. Realistic interpretation of the complex interactions between rock deformation, fluid flow, heat transfer, and fracture propagation induced by fluid injection is important for fracture network design. In this work, numerical models are developed to simulate rock failure and hydraulic fracture propagation. The influences of rock deformation, fluid flow, and heat transfer on fracturing processes are studied using a coupled thermo-hydro-mechanical (THM) analysis. The models are used to simulate microscopic and macroscopic fracture behaviors of laboratory-scale uniaxial and triaxial experiments on rock using an elastic/brittle damage model considering a stochastic heterogeneity distribution. The constitutive modeling by the energy release rate-based damage evolution allows characterizing brittle rock failure and strength degradation. This approach is then used to simulate the sequential process of heterogeneous rock failures from the initiation of microcracks to the growth of macrocracks. The hydraulic fracturing path, especially for fractures emanating from inclined wellbores and closed natural fractures, often involves mixed mode fracture propagation. Especially, when the fracture is inclined in a 3D stress field, the propagation cannot be modeled using 2D fracture models. Hence, 2D/3D mixed-modes fracture growth from an initially embedded circular crack is studied using the damage mechanics approach implemented in a finite element method. As a practical problem, hydraulic fracturing stimulation often involves fluid pressure change caused by injected fracturing fluid, fluid leakoff, and fracture propagation with brittle rock behavior and stress heterogeneities. In this dissertation, hydraulic fracture propagation is simulated using a coupled fluid flow/diffusion and rock deformation analysis. Later THM analysis is also carried out. The hydraulic forces in extended fractures are solved using a lubrication equation. Using a new moving-boundary element partition methodology (EPM), fracture propagation through heterogeneous media is predicted simply and efficiently. The method allows coupling fluid flow and rock deformation, and fracture propagation using the lubrication equation to solve for the fluid pressure through newly propagating crack paths. Using the proposed model, the 2D/3D hydraulic fracturing simulations are performed to investigate the role of material and rock heterogeneity. Furthermore, in geothermal and petroleum reservoir design, engineers can take advantage of thermal fracturing that occurs when heat transfers between injected flow and the rock matrix to create reservoir permeability. These thermal stresses are calculated using coupled THM analysis and their influence on crack propagation during reservoir stimulation are investigated using damage mechanics and thermal loading algorithms for newly fractured surfaces. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/150961

Simulation of Hydraulic Fractures and Their Interactions with Natural Fractures

Simulation of Hydraulic Fractures and Their Interactions with Natural Fractures
Author : Varahanaresh Sesetty
Publisher : Unknown
Release Date : 2012
Category :
Total pages :129
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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.

Mathematical Modeling and Simulation Analysis of Hydraulic Fracture Propagation in Three-layered Poro-elastic Media

Mathematical Modeling and Simulation Analysis of Hydraulic Fracture Propagation in Three-layered Poro-elastic Media
Author : Anonim
Publisher : Unknown
Release Date : 1992
Category :
Total pages :278
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Hydraulic fracturing plays a pivotal role in the enhancement of oil and gas production recovery from low permeability reservoirs. The process of hydraulic fracturing entails the generation of a fracture by pumping fluids blended with special chemicals and proppants into the payzone at high injection rates and pressures to extend and wedge fractures. The mathematical modeling of hydraulically induced fractures generally incorporates coupling between the formation elasticity, fracture fluid flow, and fracture mechanics equations governing the formation structural responses, fluid pressure profile, and fracture growth. Two allied unsymmetric elliptic fracture models are developed for fracture configuration evolutions in three-layered rock formations. The first approach is based on a Lagrangian formulation incorporating pertinent energy components associated with the formation structural responses and fracture fluid flow. The second model is based on a generalized variational principle, introducing an energy rate related functional. These models initially simulate a penny-shaped fracture, which becomes elliptic if the crack tips encounters (upper and/or lower) barriers with differential reservoir properties (in situ stresses, 16 elastic moduli, and fracture toughness-contrasts and fluid leak-off characteristics). The energy rate component magnitudes are determined to interpret the governing hydraulic fracture mechanisms during fracture evolution. The variational principle is extended to study the phenomenon and consequences of fluid lag in fractures. Finally, parametric sensitivity and energy rate investigations to evaluate the roles of controllable hydraulic treatment variables and uncontrollable reservoir property characterization parameters are performed. The presented field applications demonstrate the overall capabilities of the developed models. These studies provide stimulation treatment guidelines for fracture configuration design, control, and optimization.

Real-time and Post-frac' 3-D Analysis of Hydraulic Fracture Treatments in Geothermal Reservoirs

Real-time and Post-frac' 3-D Analysis of Hydraulic Fracture Treatments in Geothermal Reservoirs
Author : Anonim
Publisher : Unknown
Release Date : 1994
Category :
Total pages :129
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Economic power production from Hot Dry Rock (HDR) requires the establishment of an efficient circulation system between wellbores in reservoir rock with extremely low matrix permeability. Hydraulic fracturing is employed to establish the necessary circulation system. Hydraulic fracturing has also been performed to increase production from hydrothermal reservoirs by enhancing the communication with the reservoir's natural fracture system. Optimal implementation of these hydraulic fracturing applications, as with any engineering application, requires the use of credible physical models and the reconciliation of the physical models with treatment data gathered in the field. Analysis of the collected data has shown that 2-D models and 'conventional' 3-D models of the hydraulic fracturing process apply very poorly to hydraulic fracturing in geothermal reservoirs. Engineering decisions based on these more 'conventional' fracture modeling techniques lead to serious errors in predicting the performance of hydraulic fracture treatments. These errors can lead to inappropriate fracture treatment design as well as grave errors in well placement for hydrothermal reservoirs or HDR reservoirs. This paper outlines the reasons why conventional modeling approaches fall short, and what types of physical models are needed to credibly estimate created hydraulic fracture geometry. The methodology of analyzing actual measured fracture treatment data and matching the observed net fracturing pressure (in realtime as well as after the treatment) is demonstrated at two separate field sites. Results from an extensive Acoustic Emission (AE) fracture diagnostic survey are also presented for the first case study aS an independent measure of the actual created hydraulic fracture geometry.

Poroelastic and Poroplastic Modeling of Hydraulic Fracturing

Poroelastic and Poroplastic Modeling of Hydraulic Fracturing
Author : HanYi Wang
Publisher : Unknown
Release Date : 2014
Category : Petroleum engineering
Total pages :129
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It is essential to predict the behavior of hydraulic fractures accurately based on the understanding of fundamental mechanisms, governing process. The prevailing approach for hydraulic fracture modeling relies on Linear Elastic Fracture Mechanics (LEFM) that gives reasonable predictions for hard rock hydraulic fracturing, but often fails to give accurate predictions of fracture geometry and propagation pressure in soft/unconsolidated formation. The reasons are that the fracture process zone ahead of the crack tip, elasto-plastic material behavior and strong coupling between flow and stress cannot be neglected in these formations. In this study, we developed a fully coupled poroelastic and poroplastic hydraulic fracturing model with cohesive zone method. The impact of formation plastic properties on fracture process is investigated. The results indicate that formation plastic behavior can have a great impact on fracture net pressure and geometry, especially when the plastic deformation area is large.

A Pkn Hydraulic Fracture Model Study and Formation Permeability Determination

A Pkn Hydraulic Fracture Model Study and Formation Permeability Determination
Author : Jing Xiang
Publisher : Unknown
Release Date : 2012
Category :
Total pages :129
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Hydraulic fracturing is an important method used to enhance the recovery of oil and gas from reservoirs, especially for low permeability formations. The distribution of pressure in fractures and fracture geometry are needed to design conventional and unconventional hydraulic fracturing operations, fracturing during water-flooding of petroleum reservoirs, shale gas, and injection/extraction operation in a geothermal reservoir. Designing a hydraulic fracturing job requires an understanding of fracture growth as a function of treatment parameters. There are various models used to approximately define the development of fracture geometry, which can be broadly classified into 2D and 3D categories. 2D models include, the Perkins-Kern-Nordgren (PKN) fracture model, and the Khristianovic-Geertsma-de. Klerk (KGD) fracture model, and the radial model. 3D models include fully 3D models and pseudo-three-dimensional (P-3D) models. The P-3D model is used in the oil industry due to its simplification of height growth at the wellbore and along the fracture length in multi-layered formations. In this research, the Perkins-Kern-Nordgren (PKN) fracture model is adopted to simulate hydraulic fracture propagation and recession, and the pressure changing history. Two different approaches to fluid leak-off are considered, which are the classical Carter's leak-off theory with a constant leak-off coefficient, and Pressure-dependent leak-off theory. Existence of poroelastic effect in the reservoir is also considered. By examining the impact of leak-off models and poroelastic effects on fracture geometry, the influence of fracturing fluid and rock properties, and the leak-off rate on the fracture geometry and fracturing pressure are described. A short and wide fracture will be created when we use the high viscosity fracturing fluid or the formation has low shear modulus. While, the fracture length, width, fracturing pressure, and the fracture closure time increase as the fluid leak-off coefficient is decreased. In addition, an algorithm is developed for the post-fracture pressure-transient analysis to calculate formation permeability. The impulse fracture pressure transient model is applied to calculate the formation permeability both for the radial flow and linear fracture flow assumption. Results show a good agreement between this study and published work.

Analysis of Hydraulic Fracture Propagation in Fractured Reservoirs

Analysis of Hydraulic Fracture Propagation in Fractured Reservoirs
Author : Arash Dahi Taleghani
Publisher : Unknown
Release Date : 2009
Category : Gas reservoirs
Total pages :394
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Large volumes of natural gas exist in tight fissured reservoirs. Hydraulic fracturing is one of the main stimulating techniques to enhance recovery from these fractured reservoirs. Although hydraulic fracturing has been used for decades for the stimulation of tight gas reservoirs, a thorough understanding of the interaction between induced hydraulic fractures and natural fractures is still lacking. Recent examples of hydraulic fracture diagnostic data suggest complex, multi-stranded hydraulic fracture geometry is a common occurrence. The interaction between pre-existing natural fractures and the advancing hydraulic fracture is a key condition leading to complex fracture patterns. Large populations of natural fractures that exist in formations such as the Barnett shale are sealed by precipitated cements which could be quartz, calcite, etc. Even though there is no porosity in the sealed fractures, they may still serve as weak paths for fracture initiation and/or for diverting the path of the growing hydraulic fractures. Performing hydraulic fracture design calculations under these complex conditions requires modeling of fracture intersections and tracking fluid fronts in the network of reactivated fissures. In this dissertation, the effect of the cohesiveness of the sealed natural fractures and the intact rock toughness in hydraulic fracturing are studied. Accordingly, the role of the pre-existing fracture geometry is also investigated. The results provide some explanations for significant differences in hydraulic fracturing in naturally fractured reservoirs from non-fractured reservoirs. For the purpose of this research, an extended finite element method (XFEM) code is developed to simulate fracture propagation, initiation and intersection. The motivation behind applying XFEM are the desire to avoid remeshing in each step of the fracture propagation, being able to consider arbitrary varying geometry of natural fractures and the insensitivity of fracture propagation to mesh geometry. New modifications are introduced into XFEM to improve stress intensity factor calculations, including fracture intersection criteria into the model and improving accuracy of the solution in near crack tip regions. The presented coupled fluid flow-fracture mechanics simulations extend available modeling efforts and provide a unified framework for evaluating fracture design parameters and their consequences. Results demonstrate that fracture pattern complexity is strongly controlled by the magnitude of in situ stress anisotropy, the rock toughness, the natural fracture cement strength, and the approach angle of the hydraulic fracture to the natural fracture. Previous studies (mostly based on frictional fault stability analysis) have concentrated on predicting the onset of natural fracture failure. However, the use of fracture mechanics and XFEM makes it possible to evaluate the progression of fracture growth over time as fluid is diverted into the natural fractures. Analysis shows that the growing hydraulic fracture may exert enough tensile and/or shear stresses on cemented natural fractures that they may be opened or slip in advance of hydraulic fracture tip arrival, while under some conditions, natural fractures will be unaffected by the hydraulic fracture. A threshold is defined for the fracture energy of cements where, for cases below this threshold, hydraulic fractures divert into the natural fractures. The value of this threshold is calculated for different fracture set orientations. Finally, detailed pressure profile and aperture distributions at the intersection between fracture segments show the potential for difficulty in proppant transport under complex fracture propagation conditions. Whether a hydraulic fracture crosses or is arrested by a pre-existing natural fracture is controlled by shear strength and potential slippage at the fracture intersections, as well as potential debonding of sealed cracks in the near-tip region of a propagating hydraulic fracture. We introduce a new more general criterion for fracture propagation at the intersections. We present a complex hydraulic fracture pattern propagation model based on the Extended Finite Element Method as a design tool that can be used to optimize treatment parameters under complex propagation conditions.

Hydraulic Fracture Mechanics

Hydraulic Fracture Mechanics
Author : Peter Valkó,Michael J. Economides
Publisher : Wiley-Blackwell
Release Date : 1995
Category : Technology & Engineering
Total pages :298
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The book explores the theoretical background of one of the most widespread activities in hydrocarbon wells, that of hydraulic fracturing. A comprehensive treatment of the basic phenomena includes: linear elasticity, stresses, fracture geometry and rheology. The diverse concepts of mechanics are integrated into a coherent description of hydraulic fracture propagation. The chapters in the book are cross-referenced throughout and the connections between the various phenomena are emphasized. The book offers readers a unique approach to the subject with the use of many numerical examples.