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Research Papers: Petroleum Engineering

# Casing Burst Strength Degradation Due to Casing Wear

[+] Author and Article Information
Changning Li

Well Engineering Research Center
for Intelligent Automation,
University of Houston,
Houston, TX 77004

Robello Samuel

Halliburton,
10200 Bellaire Boulevard,
Houston, TX 77072

Contributed by the Petroleum Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received May 6, 2017; final manuscript received June 14, 2017; published online September 28, 2017. Editor: Hameed Metghalchi.

J. Energy Resour. Technol 140(3), 032901 (Sep 28, 2017) (8 pages) Paper No: JERT-17-1205; doi: 10.1115/1.4037351 History: Received May 06, 2017; Revised June 14, 2017

## Abstract

Casing integrity management is crucial, especially in wells experiencing severe casing wall degradation. Knowledge of stress distribution in worn casing helps predict where a casing failure occurs first. In industrial practice, a common method is to estimate the reduction of the casing burst strength in worn casing using API burst strength equation with a linear reduction in the remaining wall thickness or wear percentage equivalent to a “uniform-worn” casing model. This study focuses on building a rigorous engineering model for burst strength degradation prediction based on “crescent shape” casing wear. This model calculates the hoop strength directly, including the local bending in the thinner portion of the “crescent-worn” casing. This paper has developed a mathematical model to calculate the hoop strength of worn out casing with force and moment balance equations. This study finds the calculation of reduced strength using the linear wear model to be overly conservative because it only focuses on the stress at the thinnest portion of the worn casing. The stress predicted in this paper is similar to the results obtained from the finite element method (FEM), which validates equations and results obtained from this paper. The developed model is generic and can apply to casings, risers, and tubings.

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## References

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## Figures

Fig. 4

Crescent shape model derivation

Fig. 3

Crescent-shaped wear model geometrical configuration

Fig. 2

Simplification method of uniformly worn out model

Fig. 1

Tool joint in contact with casing in directional drilling

Fig. 10

Pressure difference between crescent model and API model with varied d/t ratio

Fig. 5

Worn casing with 5 in OD burst capacity prediction comparison

Fig. 6

Worn casing with 7 in OD burst capacity prediction comparison

Fig. 7

Worn casing with 9 5/8 in OD burst capacity prediction comparison

Fig. 8

Worn casing with 13 3/8 in OD burst capacity prediction comparison

Fig. 9

Pressure difference between crescent model and API model with varied d/t ratio

Fig. 13

FEM in ANSYS

Fig. 11

Multiwear scenario where wear position is close

Fig. 12

Multiwear scenario where wear position is far apart

Fig. 14

Worn casing deformation before burst failure

Fig. 15

Geometrical configuration with multiple casing wears

Fig. 16

Critical section of multiple casing wears scenarios

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