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Research Papers: Petroleum Engineering

Full Fluid–Solid Cohesive Finite-Element Model to Simulate Near Wellbore Fractures

[+] Author and Article Information
Saeed Salehi

Assistant Professor
Petroleum Engineering,
University of Louisiana at Lafayette,
104 University Circle,
Lafayette, LA 70504
e-mail: saeads@gmail.com

Runar Nygaard

Associate Professor
Missouri University of Science and Technology,
129 McNutt,
1400 N. Bishops Avenue,
Rolla, MO 65401
e-mail: nygaardr@mst.edu

Contributed by the Petroleum Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received January 2, 2014; final manuscript received May 6, 2014; published online August 27, 2014. Assoc. Editor: Christopher J. Wajnikonis.

J. Energy Resour. Technol 137(1), 012903 (Aug 27, 2014) (9 pages) Paper No: JERT-14-1003; doi: 10.1115/1.4028251 History: Received January 02, 2014; Revised May 06, 2014

This paper presents finite-element simulation for hydraulic fracture's initiation, propagation, and sealing in the near wellbore region. A full fluid solid coupling module is developed by using pore pressure cohesive elements. The main objective of this study is to investigate the hypothesis of wellbore hoop stress increase by fracture sealing. Anisotropic stress state has been used with assignment of individual criteria for fracture initiation and propagation. Our results demonstrate that fracture sealing in “wellbore strengthening” cannot increase the wellbore hoop stress beyond its upper limit when no fractures exist. However, this will help to restore part or all of the wellbore hoop stress lost during fracture propagation.

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References

Figures

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Fig. 1

Traction–separation law for cohesive zone modeling

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Fig. 2

Fluid flow into cohesive elements considering both tangential and normal flows

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Fig. 3

Loading experiments for cohesive elements properties

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Fig. 4

Finite element analysis poro-elastic model details including boundary conditions

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Fig. 5

Calculation error for simulations with different element types comparing to analytical solution

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Fig. 8

Hoop stress around the wellbore after fracture sealed (second line from top), after fracture propagated (bottom line), after fracture initiated (dashed line), and for intact wellbore (top line)

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Fig. 9

Stress profile in cohesive elements direction for intact case (left) and after fracture propagation (right, fracture size has been magnified)

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Fig. 10

Pore pressure distribution in the model

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Fig. 11

Effect of different parameters on maximum fracture opening based on normalized values

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Fig. 6

Radial stress versus distance based on different ratios of model size over borehole diameter

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Fig. 7

A schematic of the steps required in the simulations for fracture sealing based on a typical XLOT

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Fig. 12

(a) Fracture openings from cohesive model and KGD analytical model. (b) Fracture pressures from cohesive model and KGD analytical model.

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