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Framework for Field-Based Annular Pressure Prediction in Horizontal Directional Drilling
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- Author / Creator
- Inshik Park
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There have been attempts by many researchers over the years to improve the prediction of Inadvertent Return (IR) during Horizontal Directional Drilling (HDD). An analytical model of the maximum allowable mud pressure during HDD, Pmax, has been commonly referred as “Delft method” and it has been broadly used among the practitioners over the past thirty years. Since the Delft method is generally accepted for HDD designs, most of the research has focused on improving the accuracy of estimated Pmax compared to the actual annular pressure measured during the field operation. Despite the advantages with Delft method for its simplicity in procedure of estimating Pmax and its logical explanation on connecting the cavity expansion theory to the HDD borehole stability; its tendency of overprediction have been reported by multiple researchers. Until lately, researchers mainly focused on reducing the size of plastic zone as an application of the factor of safety, or applying additional factor of safety as 1.5 or 2.0 on top of the calculated Pmax. However, instead of merely applying a vague number for the factor of safety, it was thought to be more logical and efficient to suggest an appropriate factor of safety, corresponding to the risk of the operation. Depending on the depth of the borehole, surrounding soil type, sensitivity of project, etc., the factor to ensure the safe operation might vary. Moreover, accuracy of Pmax estimated with Delft method is significantly affected by its input geotechnical parameters: c, Su, φ, and G; however, determination of the geotechnical parameters with current practice of using SPT often poses challenges. Even though SPT provides N-value that indexes in-situ characteristics of soil, it does not include direct measurements of the geotechnical parameters; therefore, error from approximation of geotechnical parameters may lead into inaccuracy of estimation of Pmax. To conserve the preference of SPT and Delft method among the HDD industry and improve the accuracy of estimation of Pmax, a design guideline for SPT-based Pmax prediction with a framework for the factor of safety was established and introduced in this thesis. Correlations between the N-value and geotechnical parameters: c, Su, φ, and G, which were found from multiple literatures, were evaluated and introduced into Delft equation with a conservative margin of error; moreover, resulting algorithm of the SPT-based method was also presented as a flowchart. The framework for the factor of safety was set up and specified for each possible scenario of HDD operation to allow designers to predict the limiting pressure with factors of safety tailored to the specific project. This proposed guideline was validated with the hydrofracture pressure measurements, those were provided from laboratory experiments of Queen’s university and case studies of the actual HDD operations.
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- Graduation date
- Fall 2020
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.