Prediction and Evaluation of Annular Pressure in Horizontal Directional Drilling
A thesis submitted in partial fulfillment of the requirements for the degree of
Doctor of Philosophy
Construction Engineering and Management
Department of Civil and Environmental Engineering
University of Alberta
Ali Rostami, 2017
Horizontal directional drilling (HDD) is a crossing technique for the oil and gas, utilities,
and infrastructure sectors for pipeline installations in different situations under natural or
manmade obstacles. This technology was acquired from oil well drilling industry and was
adopted in HDD. The environmental and social impacts caused by a lack of good practice in
borehole drilling are major threats to the trenchless industry, especially to HDD. Although HDD
technology has many advantages over open-cut methods, it sometimes carries the risk of loss of
drilling fluid circulation, hydraulic fracture of the ground, and borehole collapse due to a lack of
proper annular pressure management. Annular pressure (plan pressure) and maximum allowable
pressure predictions are critical issues for annular pressure management. During HDD operation,
annular pressure must not exceed the maximum allowable pressure to minimize the risk of
hydraulic fracturing, which leads to loss of drilling fluid and increase in overall project risk.
This study aims to identify the shortcomings of common industrial methods in current
HDD practices due to poor annular pressure management. Furthermore, this study intends to
propose a scheme for better annular pressure management. To achieve this objective, the plan
pressure and maximum allowable pressure during HDD operations must be estimated; however,
the methods presently utilized by industry are not accurate. In the case of plan pressure
estimation, the Bingham plastic model is commonly used in HDD operations to estimate the
annular pressure. However, the Bingham plastic model overestimates the annular pressure,
leading to incorrect bore path design and erroneous information from down-hole conditions. In
the case of estimating the maximum allowable pressure of the drilling fluid, the Delfts cavity
expansion method is commonly used. The Delfts method significantly overestimates the
maximum allowable pressure of the drilling fluid due to its simplified assumptions and can lead
to hydraulic fracture of the ground during HDD operations.
This study introduces two methods extracted from the American Petroleum Institute
(API) to estimate the plan pressure according to the power-law and Bingham plastic models,
which are adjusted and modified for HDD operation during pilot boring. Prior to calculating the
annular pressure, it is assumed that the borehole is under an ideal condition in which the
borehole radius is not changed and the pressure loss and infiltration of drilling fluid are
negligible. To understand the infiltration of drilling fluid into the adjacent soil, a series of
experimental tests on the sandy soil have been conducted to show the formation of cake around
the wellbore during HDD operation. The formation of the cake in high permeable soils such as
sand prevents drilling fluid from infiltrating into the ground; however, the infiltration of the
drilling fluid into the low permeable soil (e.g., clay) is negligible.
To estimate the maximum allowable pressure of the drilling fluid during HDD operation
in non-cohesive soil, a new approach has been introduced to overcome the improper estimations
based on Delfts method. This study has attempted to illustrate the lack of correlation between
the allowable plastic radius and the failure pressure. This correlation has been applied in industry
to the Delfts cavity expansion method and Yu and Houlsbys (1991) large strain cavity
expansion method and has resulted in an overestimation of the failure pressure. The new
approach is formulated based on the calculation of limit pressure using Yu and Houlsbys (1991)
large-strain cavity expansion method. The suggested limit pressure approach has been advanced
further to obtain a practical and useful solution to estimate the failure pressure in different
geotechnical conditions by providing a coefficient of limit pressure following the Yu and
Houlsbys (1991) method. To achieve this objective, the commercial finite element program
ABAQUS has been used to estimate the failure pressure based on the limit pressure approach
and correlates it with Yu and Houlsblys (1991) failure pressure. The coefficient of limit pressure
is determined as a function of model and soil parameters (overburden depth, friction angle, and
elastic modulus), and the significance of these parameters have been identified based on a
To verify the developed methods for plan pressure estimation, two HDD case studies
have been used. The proposed rheological models (Power Law, and modified Bingham models)
have improved the accuracy of estimation of the annular pressure during pilot boring while the
common industry methods (Bingham plastic model) significantly overestimate the annular
pressure. Moreover, to verify the new approach for estimating the maximum allowable pressure
of the drilling fluid, several experimental and field case studies from previous research have been
used. In the current study, several graphs have been generated to calculate the coefficient of limit
pressure to estimate the failure pressure properly. The new approach on annular pressure
management enables engineers to better predict and monitor the annular pressure in the borehole
during the HDD operation. This allows engineers to diagnose and prevent any upcoming issues
during drilling and estimate the maximum allowable pressure of the drilling fluid to mitigate the
risks associated with high annular pressure in the borehole during HDD operation.
This dissertation is an original work that I conducted and presented in paper format. For
all of the papers, I am the first author and responsible for the numerical and analytical
calculations, experiments, and manuscripts. Dr. Yi has reviewed the manuscripts and provided
essential feedback to improve the manuscripts. My supervisor, Dr. Bayat, has set the objectives
of the studies and monitored the research process. He is the corresponding author for all the
Chapter 3 of this dissertation has been accepted for publication as Rostami, A., Deng, S.,
Yi, Y., Kang, C., and Bayat, A., (2017). Initial Experimental Study on Formation of Filter Cake
in Sand during Horizontal Directional Drilling. NASTT No-Dig Show Conference, Washington,
Chapter 4 of this dissertation has been published in: Rostami, A., Yi, Y., Osbak, M., and
Bayat, A. (2016). Annular Pressure Prediction in HDD using the Bingham Plastic Flow Model.
International Journal of Petroleum Engineering, 2(2), 79-90.
Chapter 5 of this dissertation has been published in: Rostami, A., Yi, Y., Bayat, A., and
Osbak, M. (2015). Predicting the Plan Annular Pressure Using the Power Law Flow Model in
Horizontal Directional Drilling. Canadian Journal of Civil Engineering, 43(3), 252-259.
Chapter 6 of this dissertation has been published in: Rostami, A., Yi, Y., and Bayat, A.
(2016). Estimation of Maximum Annular Pressure during HDD in Non cohesive Soils.
International Journal of Geomechanics, ASCE, 06016029.
Chapter 7 of this dissertation has been submitted to the Geomechanics and
Geoengineering: An International Journal by Rostami, A., Kang, C., Yi, Y., and Bayat, A.
Numerical Modeling of the Failure Pressure during Horizontal Directional Drilling in Non-
The co-authors of the aforementioned manuscripts actively assisted the first author in
writing and revising the manuscripts.
who taught me the lesson of resistance and patience
who taught me the lesson of love
I would like to express my gratitude to my supervisor, Dr. Alireza Bayat, for giving me
this great opportunity to work on such a challenging topic. His valuable guidance, patience,
encouragement, and financial support will always be acknowledged.
I would like to express my gratitude to my final exam committee members Dr. Erez
Allouche, Dr. Dave Chan, Dr. Roger Cheng, Dr. Huazhou (Andy) Li, Dr. Vivek Bindiganavile,
and Dr. Alireza Bayat for their insightful suggestions and comments to improve my dissertation.
I would also like to sincerely appreciate the contributions of my supervisor committee members,
Dr. Dave Chan and Dr. Roger Cheng, to my dissertation before my PhD defence exam. I would
also like to thank Dr. Yaolin Yi and Dr. Chao Kang, the postdoctoral fellows in our research
group at the University of Alberta, for their peer review of my manuscripts and constructive
comments on my research study. I would also like to thank our professional editors at CETT,
Tejay Gardiner, Lauren Wozny, Tatiana Boryshchuk, and Sheena Moore, for their great editorial
Finally, I would like to express my deep gratitude to T