Zhang, Yixuan
(2019)
Stress Dependence of the Burst Experiment for Determining Fracture Toughness.
Master's Thesis, University of Pittsburgh.
(Unpublished)
Abstract
The so-called “burst experiment” is used in the petroleum industry to measure the fracture toughness of reservoir rocks. It is considered advantageous compared to other methods because it tests rocks subjected to confining stress, which is more like field conditions. However, recent numerical simulations show that the burst experiment is possibly fundamentally dependent on the confining stress in a way which is not considered in the analysis of the experimental data. The reason is existence of a period of stable crack growth prior to the unstable “burst”. This stable growth is difficult to detect, and it raises large uncertainty in the crack length used in analysis of results.
In this thesis, a series of modified burst experiments with acoustic emission (AE) detection have been carried out to compare with predictions from modeling indicating that there will be stable growth for certain combinations of specimen geometry and loading, including the geometry most commonly used by industry. These tests give rise to evidence of stable growth before specimen rupture from two aspects. One is the difference between stable and unstable growth cases from AE records. The other is the behavior of calculated fracture toughness results. A criterion for spurious dependence of KIC on confining stress for cases with stable growth is then specified based on stability of the specimen after failure. Also, the results of experiments using unstable configurations provide more self-consistent estimates of fracture toughness, most notably shown in a series of burst experiments with only unstable growth showing a positive correlation between fracture toughness and confining pressure, which is consistent with typical observations in the literature. Finally, in other types of experiments with fixed confinement, a range of geometry and loading for valid calculation of KIC is indicated based on the global stability criterion, providing guidance for improved design of this widely-used test method.
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Details
| Item Type: |
University of Pittsburgh ETD
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| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
26 February 2019 |
| Defense Date: |
28 March 2019 |
| Approval Date: |
18 June 2019 |
| Submission Date: |
17 March 2019 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
71 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Chemical and Petroleum Engineering |
| Degree: |
MS - Master of Science |
| Thesis Type: |
Master's Thesis |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
burst experiment, fracture toughness, confining stress |
| Date Deposited: |
18 Jun 2019 16:49 |
| Last Modified: |
18 Jun 2019 16:49 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/36065 |
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