Method for simulating fracture toughness of layered rock based on extended finite elements

An extended finite element and fracture toughness technology, applied in the field of layered rock fracture toughness simulation based on extended finite element, can solve the problems of large amount of calculation, difficult to accurately capture the crack propagation process, etc., and achieve the effect of accurate calculation

Active Publication Date: 2020-08-04
SOUTHWEST PETROLEUM UNIV
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  • Summary
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  • Claims
  • Application Information

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Problems solved by technology

At present, there are many numerical methods for the fracture toughness of layered rocks, but the existing methods perform high-density meshing in areas of high stress and deformation concentration, such as the crack tip, and need to re-mesh in the process of fracture initiation and propagation to It is difficult to accurately capture the real fracture propagation process due to the huge amount of calculation to adapt to the fracture steering

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  • Method for simulating fracture toughness of layered rock based on extended finite elements
  • Method for simulating fracture toughness of layered rock based on extended finite elements
  • Method for simulating fracture toughness of layered rock based on extended finite elements

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Embodiment 1

[0027] Such as figure 1 A method for simulating the fracture toughness of layered rocks based on extended finite elements is shown, including the following steps:

[0028] A. According to the physical parameters of the layered rock and the geometric parameters of the experimental specimens, a Brazilian disc numerical model based on the extended finite element simulation of fracture toughness is established;

[0029] B. Using the extended finite element method, considering the displacement jump on both sides of the crack unit, by releasing the degree of freedom of the crack tip node, the crack initiation and expansion are simulated; the bedding distribution in the rock mass is described by defining a transversely isotropic material characteristics, and extend the isotropic Mohr-Coulomb criterion to anisotropic layered rock mass;

[0030] C. Take the initial critical damage criterion of rock crack simulation as the maximum principal stress criterion, select the damage evolution...

Embodiment 2

[0033] This embodiment discloses a specific implementation manner on the basis of the foregoing embodiments.

[0034] A. According to the physical parameters of layered rocks and the geometric parameters of experimental specimens, the numerical model of the Brazilian disc based on the extended finite element simulation of fracture toughness, that is, the CCNBD numerical model, was established. Taking shale as an example for illustration, see Tables 1 and 2 below and figure 2 , image 3 Specific parameters of the model are shown for illustration.

[0035] Table 1. Geometric parameters of Brazilian disk specimens

[0036] Diameter (mm) 74 Thickness (mm) 30 2a 0 (mm)

18 2a 1 (mm)

52 Bulk density (g / cm 3 )

2550

[0037] Table 2. Petrophysical parameters

[0038] direction Young's modulus (GPa) Poisson's ratio Shear modulus (GPa) X 3.8e10 0.16 16.38E9 Y 1.8e10 0.1 8.18E9 Z 1.8e10 0.1 8.18E9...

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Abstract

The invention discloses a method for simulating the fracture toughness of a layered rock based on an extended finite element. The method comprises the following steps: establishing a Brazilian disc numerical model for simulating the fracture toughness based on the extended finite element; simulating and calculating crack initiation and propagation of cracks; defining a transverse isotropic material to describe bedding distribution characteristics in the rock mass, and promoting an isotropic molar-coulomb criterion to the anisotropic layered rock mass; taking an initial critical damage criterion of rock crack simulation as a maximum principal stress criterion, determining damage evolution and damage stability viscosity parameters based on an energy damage evolution type, specifying a contact effect of rock bedding, a matrix and cracks, and finally applying boundary conditions; extracting an analysis and calculation result, calculating the fracture toughness of Brazilian disc numerical simulation, comparing the fracture toughness value of the Brazilian disc in an indoor test, and for crack propagation of the Brazilian disc, comparing an analysis numerical value with a crack propagation condition in an actual test; and finally, achieving accurate simulation of a crack propagation path and a fracture toughness value.

Description

technical field [0001] The invention relates to the technical field of petroleum exploitation, in particular to a method for simulating the fracture toughness of layered rocks based on extended finite elements. Background technique [0002] Reservoirs such as shale oil and gas and tight oil and gas are different from conventional gas reservoirs and have the characteristics of self-generation and self-storage. At the same time, their reservoir characteristics are characterized by extremely low porosity and low permeability. Therefore, complex fracture networks must be formed through volume fracturing technology. for efficient development. Fracture toughness of rock is a key parameter in hydraulic fracturing design. The correct prediction of fracture toughness can quantitatively evaluate the compressibility of reservoirs and provide reference for fracture network morphology during fracturing. [0003] Fracture toughness, also known as the critical stress intensity factor, can...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G06F30/23
Inventor 刘向君张景轩王万彬袁峰王明星李佳琦陈超峰
Owner SOUTHWEST PETROLEUM UNIV
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