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Research Papers

Simulation-Based Unitary Fracking Condition and Multiscale Self-Consistent Fracture Network Formation in Shale

[+] Author and Article Information
Qinglei Zeng, Tao Wang, Zhanli Liu

Applied Mechanics Laboratory,
School of Aerospace Engineering,
Tsinghua University,
Beijing 100084, China

Zhuo Zhuang

Applied Mechanics Laboratory,
School of Aerospace Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: zhuangz@tsinghua.edu.cn

1Corresponding author.

Manuscript received December 27, 2016; final manuscript received March 7, 2017; published online March 24, 2017. Editor: Yonggang Huang.

J. Appl. Mech 84(5), 051004 (Mar 24, 2017) (7 pages) Paper No: JAM-16-1623; doi: 10.1115/1.4036192 History: Received December 27, 2016; Revised March 07, 2017

Hydraulic fracturing (fracking) technology in gas or oil shale engineering is highly developed last decades, but the knowledge of the actual fracking process is mostly empirical and makes mechanicians and petroleum engineers wonder: why fracking works? (Bažant et al., 2014, “Why Fracking Works,” ASME J. Appl. Mech., 81(10), p. 101010) Two crucial issues should be considered in order to answer this question, which are fracture propagation condition and multiscale fracture network formation in shale. Multiple clusters of fractures initiate from the horizontal wellbore and several major fractures propagate simultaneously during one fracking stage. The simulation-based unitary fracking condition is proposed in this paper by extended finite element method (XFEM) to drive fracture clusters growing or arresting dominated by inlet fluid flux and stress intensity factors. However, there are millions of smeared fractures in the formation, which compose a multiscale fracture network beyond the computation capacity by XFEM. So, another simulation-based multiscale self-consistent fracture network model is proposed bridging the multiscale smeared fractures. The purpose of this work is to predict pressure on mouth of well or fluid flux in the wellbore based on the required minimum fracture spacing scale, reservoir pressure, and proppant size, as well as other given conditions. Examples are provided to verify the theoretic and numerical models.

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Figures

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Fig. 1

Simultaneous propagation of multiple fractures during one fracking stage

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Fig. 2

Simultaneous propagation of four HFs

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Fig. 3

Fluid partitioning and evolution of f for case 1

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Fig. 4

Fluid partitioning and evolution of f for case 2

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Fig. 5

Fluid partitioning and evolution of f for case 3

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Fig. 6

Fluid partitioning and evolution of f for case 4

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Fig. 7

Global fracture network from local fracture SRV model

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Fig. 8

The smallest fracture spacing 0.1 m is established after five scale reduction from the largest scale level at 30 m

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Fig. 9

The fracture propagation process at the smallest scale

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Fig. 10

Fracture width and formation deformation contour at different scales

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Fig. 11

Average fracture width versus minimum fracture spacing at different scales

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