In-Situ Stress Analysis of Southwest Saskatchewan
Total Page:16
File Type:pdf, Size:1020Kb
In-Situ Stress Analysis of Southwest Saskatchewan A Thesis Submitted to the College of Graduate Studies and Research In Partial Fulfillment of the Requirements For the Degree of Master of Science In the Department of Civil and Geological Engineering University of Saskatchewan, Saskatoon, SK, Canada By Osman Hamid © Copyright Osman Hamid, February, 2008: All rights reserved PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a degree of Master of Science from the University of Saskatchewan, I agree that the Libraries of this University may make it freely available for inspection. I further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor or professors who supervised my thesis work or, in their absence, by the Head of the Department or the Dean of the College in which my thesis work was done. It is understood that any copying or publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Saskatchewan in any scholarly use which may be made of any material in my thesis. Head of the Department of Civil and Geological Engineering University of Saskatchewan Engineering Building 57 Campus Drive Saskatoon, Saskatchewan Canada S7N 5A9 Osman Hamid February 20, 2008 i ABSTRACT Scenarios developed by the National Energy Board of Canada predict that Canadian unconventional gas production, including coalbed methane (CBM), may be required to meet Canadian energy demands by the year 2008, and could constitute up to 65% of supply by 2025. Although there has been considerable CBM exploration and development in Alberta in recent years, there has been relatively limited activity in Saskatchewan. The in-situ stress regime can have a strong influence on coal bed methane (CBM) production, coal permeability, hydraulic fracturing pressure, and borehole stability while drilling horizontal wells. A limited number of stress regime analyses have been conducted previously on a regional scale, for the entire Western Canada Sedimentary Basin (WCSB), but none has been conducted with a focus on Saskatchewan. The primary objective of this study was to investigate in-situ stress magnitudes and orientations in southwestern Saskatchewan. The secondary objective was to quantify the influence of in- situ stresses on operational practices that would be used to exploit CBM targets. Analysis of vertical stress magnitudes and gradients were conducted using bulk density data compiled for 257 wells in southwest Saskatchewan. Vertical stress magnitudes calculated at the base of the Belly River Formation in the region where its CBM potential is greatest were found to be in the 6 to 12 MPa range. Vertical stress magnitudes at the top of the Mannville Group in the region where its CBM potential is greatest were found to be in the 12 to 18 MPa range. Data available for interpretation of minimum horizontal stress magnitudes were considerably more limited. A technique was developed to estimate these magnitudes using fracture stimulation data, which were available for the Viking Formation and Mannville Groups. Using this technique, minimum horizontal stress magnitudes at the top of the Mannville Group in the region of greatest interest were estimated to be 10 to 14 MPa. The results of these analyses suggest that depth is a dominant controlling factor for minimum horizontal stress magnitude, but that pore pressures (sub-normal pressures cause lower stresses) and lithology (shaley rocks, and perhaps coals, have higher stresses) also have notable effects. Insufficient data were obtained for direct estimation of minimum horizontal stresses in the Belly River ii Formation. Minimum horizontal stress magnitudes in this formation might be quite close to vertical stress magnitudes. Borehole breakouts were analyzed to interpret the orientation of maximum horizontal stress (σHmax) in the study area. The mean orientation of the mean borehole breakouts gives a 137º with a circular standard deviation of 12º, which parallels the minimum horizontal stress in the study area with a notable inflection overlying the Swift Current platform. The data is portrayed in a trajectory map. The trajectories indicated on the map can be used for predicting the orientation of induced hydraulic fractures, and the likely orientation of face cleats in coals. Knowledge of the orientations of these features is essential to effective development of CBM resources. Based on the stress and pore pressure data presented in this thesis, it is anticipated that minimum effective stresses in the Belly River coals will typically be a few MPa, and up to 10 MPa in the Mannville coals. A very rough estimate of permeabilities based on the data compiled for various Canadian coals suggests that permeabilities could be in the 0.01 to 10 millidarcy range for the former, and 0.01 to 1 millidarcy range for the latter. Borehole stability analyses were conducted for both the Belly River Formation and the Mannville Group. The results suggest that horizontal drilling of the Mannville coals should be feasible, without the need for high-density drilling muds. Given that the Belly River coals occur in numerous thin seams, they are most likely to be developed using vertical wells. Borehole instability is not likely to be a major problem in these vertical wells. Recommendations are provided for laboratory investigation of coal permeabilities and mechanical properties, field testing for minimum horizontal stress magnitudes in coal seams and adjacent strata, and additional analysis of existing fracture stimulation, log and core data for strata not analyzed in this project. iii ACKNOWLEDGEMENT To accomplish any kind of success, one person’s capabilities alone are not enough. There are several factors that contribute towards achieving one’s goals and objectives. Some of these factors include inspiration, guidance, motivation, and encouragement. While working towards completion of this thesis, several individuals have made valuable and significant contributions. I would like to express my sincere gratitude to all of those individuals. It would not be possible to name each individual, but I would like to mention some of them. Professor Hawkes, my supervisor, who from the beginning, through my work and until the end provided guidance, support, valuable advice and constant encouragement. I feel honoured to have had such a great adviser. Thanks Chris. Professor Milne, my thesis committee member, always provided me with inspiration and built a strong desire in me to work hard to succeed. I’ve learned a lot from Doug, my first rock mechanics instructor. Thanks Doug for your support. Professor Sharma, my thesis committee member, provided support, feedback and help that has proved to be very valuable. Several organizations and individuals have made significant contributions, and I would like to thank them: • The Petroleum Technology Research Centre, of Regina, provided financial support for this project, which was crucial for its success. • BJ Service Company of Canada provided valuable hydraulic fracturing data that was used for interpretation of horizontal stress magnitude. Special thanks to Robert Hawkes and Keri Yule for their support. • Craig Lamb, Chief Geoscientist with Husky Energy, provided me with motivation, guidance and data that were valuable to the project. • Nexen Inc. and EnCana Corp. were also supportive and provided data for my thesis. • Advanced Geotechnology, a Weatherford company based in Calgary, gave me a great opportunity to use their software to interpret horizontal stress magnitudes and orientations. iv • Melinda Yurkowski and Bob Troyer of Saskatchewan Industry and Resources (Geological Services / Well Information) for their advice and assistance in accessing public well data. Finally, I thank my family for their support over the years. I hope this work will make a contribution in expanding the existing knowledge of the Petroleum industry and that means so much to me. v TABLE OF CONTENTS Page PERMISSION TO USE....................................................................................................... i ABSTRACT........................................................................................................................ ii ACKNOWLEDGEMENT ................................................................................................. iv LIST OF TABLES........................................................................................................... viii LIST OF FIGURES ........................................................................................................... ix 1. INTRODUCTION ...........................................................................................................1 1.1 Background....................................................................................................... 1 1.1.1 General.............................................................................................................. 1 1.1.2 Western Canada................................................................................................ 1 1.2 Objectives ......................................................................................................... 2 1.3 Scope................................................................................................................. 3 1.4 Structure of