Reservoir Characterization of Triassic and Jurassic sandstones of Snorre Field, the northern North Sea Owais Hameed Master Thesis, Autumn 2016 Reservoir Characterization of Triassic and Jurassic sandstones of Snorre Field, the northern North Sea Owais Hameed Thesis submitted for degree of Master in Geology 60 credits Department of Mathematics and Natural Science UNIVERSITY OF OSLO December / 2016 © Owais Hameed, 2016 Tutor(s): Nazmul Haque Mondol (UiO) This work is published digitally through DUO – Digital Utgivelser ved UiO http://www.duo.uio.no It is catalogued in BIBSYS (http://www.bibsys.no/English) All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission. Preface This thesis is submitted to the Department of Geosciences, University of Oslo (UiO) in candidacy of M.Sc. degree in Geology. The research has been performed at Department of Geosciences, University of Oslo during the period of January 2016 to December 2016 under supervision of Dr. Nazmul Haque Mondol, Associate Professor, Department of Geosciences, UiO. i ii Acknowledgement I would like to express my gratitude to my supervisor Dr. Nazmul Haque Mondol, Associate Professor, Department of Geosciences, University of Oslo, for giving me the opportunity to work under his supervision and learn from his immense knowledge and experience. His guidance, patience and encouragement throughout the study helped me to complete this thesis. I am grateful to PhD candidate Mohammad Nooraipour and Irfan Baig for their precious time and help. Special thanks to Manzar Fawad and Mohammad Koochak Zadeh for their help and time when it was needed. I would like to thanks my fellow Hans-Martin, Jørgen Andre Hansen and Manvydas Saltis for our useful discussion and exchange of ideas to improve thesis. I am grateful to Tímea Gyenis for her support and encouragement during the thesis. Special thanks to all of my friends for their support. In the end, I would like to thanks my parents for their continuous support and encouragement during my study and stay in Norway. O. Hameed iii iv Abstract Reservoir characterization is one of the vital steps for hydrocarbon exploration and prospect evaluation. It improves the reservoir understanding and reduces risk during exploration. In this study a combined approach of petrophysical analysis, compaction study and rock physics diagnostic is used to understand reservoir properties and its variation with respect to burial diagenesis. The Triassic Lunde Formation and the Lower Jurassic Statfjord Formation of the Snorre field northern North Sea are investigated in this study. The Lunde Formation is principal reservoir of the Snorre field, while the Statfjord Formation is secondary reservoir due to its limited occurrence and lower thickness. A suit of well log data from 20 exploration wells was utilized to conduct this study. The Snorre field is located on the Tampen Spur area, northwest of Viking Graben in northern North Sea. The Tampen Spur is a structural high and consists of rotated fault blocks. The Lunde and Statfjord Formations are deposited on large alluvial plain during thermal subsidence phase of permo-triassic rifting phase of northern North Sea. The reservoirs consist of braided stream, single and multi-storey channel sandstones. Associated facies are fine grained overbank deposits and floodplain mudstones. Petrophysical analysis includes calculation of shale content, porosity and saturation. Petrophysical analysis shows channel sandstones have good porosity up to 23% in the Statfjord Formation and up to 18% in the Lunde Formation. The fine grained overbank deposits show less porosity. Average shale volume is observed higher in the Statfjord Formation as compared to the Lunde Formation. The rock physical properties as a function of burial depth were plotted to identify the transition of mechanical compaction to chemical compaction. The transition from mechanical compaction domain to chemical compaction domain occur between 70-90 ºC temperature at depth range between 2-2.5 km (BSF). The transition zone is marked on the basis of sharp increase in velocity which correspond grain framework stiffening due to imitation of cement. The present day temperature and geothermal gradient used to identify the transition zone. The transition occurs in same stratigraphic horizon (Lunde Formation) in most of the studied wells. The studied area is progressively subsiding basin and no regional uplift is observed. The estimated uplift along few wells is associated with rotated fault blocks and footwall uplift. Rock physics diagnostic was used to observe the effect of rock microstructures (cement and sorting) for rock properties of reservoir sandstones. The different trends of shallow buried sandstone and deeply buried sandstone are observed in rock physics effective medium models. The carbonate cement (e.g. calcite, siderite, and dolomite) also effect on rock physical properties which is observed during rock physics diagnostics. The lithology effect is observed by utilizing crossplots of Vp/Vs versus AI and LMR (Lambda-Rho versus Mu-rho). The different trends of sands and shales in Vp/Vs versus AI crossplot show good discrimination of lithology. The impact of cement is also observed in LMR crossplot, which drag data points in high rigidity area. v vi Table of contents Preface ......................................................................................................................................... i Acknowledgement ..................................................................................................................... iii Abstract ...................................................................................................................................... v Table of contents ...................................................................................................................... vii List of Figures ........................................................................................................................... xi List of tables ........................................................................................................................... xvii List of Appendices .................................................................................................................. xix Nomenclature .......................................................................................................................... xxi 1. Chapter 1: Introduction ...................................................................................................... 1 1.1 Background and motivation .......................................................................................... 1 1.2 Research objectives ....................................................................................................... 1 1.3 Study area ...................................................................................................................... 2 1.4 Database ........................................................................................................................ 3 1.5 Chapter description ....................................................................................................... 4 1.6 Limitations and future work .......................................................................................... 4 2. Chapter 2: Geology of the study area ................................................................................. 6 2.1 Geological Evolution ..................................................................................................... 6 2.2 Structural Elements ....................................................................................................... 9 2.3 General stratigraphy of the Tampen Spur ................................................................... 11 2.3.1 Hegre Group ....................................................................................................... 13 2.3.2 Statfjord Formation............................................................................................. 14 2.3.3 Dunlin Group ...................................................................................................... 15 2.3.4 Brent Group ........................................................................................................ 15 2.3.5 Viking Group ...................................................................................................... 17 2.3.6 Cromer Knoll Group ........................................................................................... 18 2.3.7 Shetland Group ................................................................................................... 18 2.3.8 Rogaland Group .................................................................................................. 18 2.3.9 Hordaland Group ................................................................................................ 18 2.3.10 Nordland Group .................................................................................................. 18 3. Chapter 3: Research methodologies and theoretical background .................................... 19 3.1 Work Flow ................................................................................................................... 19 vii 3.2 Data Handling ............................................................................................................. 20 3.2.1 Log editing and quality check ...........................................................................