Huang, Yao
(2022)
Analysis of Sleeve Fracturing and Burst Experiments for Measurement of In-Situ Stress and Rock Fracture Toughness.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Sleeve fracturing is a promising but underused field method for estimation of maximum and minimum horizontal stress in the subsurface. Similarly, the burst experiment is a laboratory technique for estimation of fracture toughness of rock under confined conditions that has been sparingly used for several decades by the petroleum industry. The techniques both involve pressurizing an uncased borehole until one or more fractures emanate from the borehole. However, ambiguity in their interpretation has led to inconsistencies and has been the primary barrier to wider adoption and full realization of the potential of these promising techniques. The main shortcoming is that previous analyses are constrained by Linear Elastic Fracture Mechanics (LEFM) or elastic stress analysis, for which the essential assumptions are violated in the vast majority of practically-relevant cases. Thus motivated, this research is aimed at simulating the behavior of fractures emanating from a pressurized borehole in both lab and field scale so that the measurements of this fracture initiation and growth can be leveraged for in-situ stress and fracture toughness estimation. The forward analysis uses cohesive zone elements in a Finite Element Analysis framework.
Working from these simulations for sleeve fracturing, a rapidly-deployable inversion algorithm is developed to estimate the maximum and minimum horizontal stress based on the field data. The results show that, combining this inversion algorithm with data that is available from recent developments in field measurements using Fiber Optic sensors, the full potential of sleeve fracturing to predict both minimum and maximum horizontal in-situ stress can be realized.
Then, turning attention to the laboratory burst experiments, the results show that choosing a 3-parameter traction-separation law for the cohesive zone model is able to capture the impact of confining stress and specimen geometry. This is a major improvement over LEFM analysis, for which ad hoc dependence of the fracture toughness on confining stress and specimen geometry must be introduced. Furthermore, the results show that running burst experiments with different specimen geometries can provide a promising path to the challenging goal of experimental characterizing a traction-separation for a given rock (or other quasi-brittle) material.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
10 June 2022 |
| Date Type: |
Publication |
| Defense Date: |
30 March 2022 |
| Approval Date: |
10 June 2022 |
| Submission Date: |
3 March 2022 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
143 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Civil and Environmental Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Inversion algorithm; size effect; Rock mechanics; geomechanics; Sleeve fracturing; In-situ stress; Maximum horizontal stress; Rock fracture toughness: cohesive zone elements: field test: |
| Date Deposited: |
10 Jun 2022 19:45 |
| Last Modified: |
10 Jun 2022 19:45 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/42314 |
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