Seismic Interpretation and Generation of Depth Surfaces for Late Palaeozoic Strata in the Irish Sea Region
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CR/16/041 Last modified: 2016/05/30 09:37 Seismic interpretation and generation of depth surfaces for late Palaeozoic strata in the Irish Sea Region Energy and Marine Geoscience Programme Commissioned Report CR/16/041 CR/16/041 Last modified: 2016/05/30 09:37 CR/16/041 Last modified: 2016/05/30 09:37 BRITISH GEOLOGICAL SURVEY ENERGY AND MARINE GEOSCIENCE PROGRAMME COMMISSIONED REPORT CR/16/041 Seismic interpretation and The National Grid and other generation of depth surfaces for Ordnance Survey data © Crown Copyright and database rights 2015. Ordnance Survey Licence late Palaeozoic strata in the Irish No. 100021290 EUL. Keywords Sea Region Palaeozoic; Irish Sea; Seismic interpretation; Structure. T C Pharaoh, K Kirk, M Quinn, M Sankey & A A Monaghan Front cover Saltom Bay, Cumberland. View looking north-west across the Solway Firth Basin toward the distant Southern Upland Massif. Rocks in the foreground comprise the Permian Cumbrian Coast Group (including Brockram) unconformable on the Whitehaven Sandstone (late Westphalian-?Stephanian). Photo: Tim Pharaoh Bibliographical reference PHARAOH, T.C., KIRK, QUINN, M, SANKEY, M. & MONAGHAN, A.A. 2016. Seismic Interpretation and generation of depth surfaces for late Palaeozoic strata in the Irish Sea Region. British Geological Survey Commissioned Report, CR/16/041. 64pp. Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail [email protected]. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract. Maps and diagrams in this book use topography based on Ordnance Survey mapping. © NERC 2016. All rights reserved Keyworth, Nottingham British Geological Survey 2016 CR/16/041 Last modified: 2016/05/30 09:37 BRITISH GEOLOGICAL SURVEY The full range of our publications is available from BGS shops at British Geological Survey offices Nottingham, Edinburgh, London and Cardiff (Welsh publications only) see contact details below or shop online at www.geologyshop.com BGS Central Enquiries Desk Tel 0115 936 3143 Fax 0115 936 3276 The London Information Office also maintains a reference collection of BGS publications, including maps, for consultation. email [email protected] We publish an annual catalogue of our maps and other publications; this catalogue is available online or from any of the Environmental Science Centre, Keyworth, Nottingham BGS shops. 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To the fullest extent permitted by law The British Geological Survey shall not be liable for any direct indirect or consequential loss or damage of any nature however caused which may result from reliance upon or use of any information contained in this report. Requests and enquiries should be addressed to Alison Monaghan, 21CXRM Palaeozoic Project Leader, [email protected]. Foreword and acknowledgements This report is a published product of the 21st Century Exploration Roadmap (21CXRM) Palaeozoic project. This joint industry-Government-BGS project comprised a regional petroleum systems analysis of the offshore Devonian and Carboniferous in the North Sea and Irish Sea. Project sponsors are thanked for data donations and their involvement at Technical Steering Committee meetings, both of which have contributed to this synthesis. Centrica are thanked for donation of 3D seismic data. Seismic companies (CGG, IHS Global Limited, WesternGeco-Schlumberger) are thanked for allowing reproduction of selected regional seismic lines and for agreeing to the release of a set of 5 km resolution grids. Richard Milton- Worssell of OGA is thanked for requesting seismic data. Seismic interpretations for some post-Permian interpretations in the East Irish Sea were provided by agreement from the CO2Stored Project, for which the assistance of Michelle Bentham is gratefully acknowledged. The assistance of John Williams in loading and quality controlling well data in the workstation environment is gratefully acknowledged. DETI are thanked for allowing re-use of seismic interpretations in the North Channel area (Quinn, 2008). Colin Tiltman (Centrica) and Christian Matthieu (OGA) are thanked for technical review of this report. Contents Foreword and acknowledgements ............................................................................................... 5 Contents ......................................................................................................................................... 5 Summary ........................................................................................................................................ 9 1 Introduction .......................................................................................................................... 10 1.1 BACKGROUND ............................................................................................................ 10 1.2 RESOURCES AVAILABLE FOR THE INTERPRETATION TASK ......................... 11 1.3 PREVIOUS BGS INTERPRETATIONS INCORPORATED .................................... 11 1.3 STRATIGRAPHICAL AND STRUCTURAL TERMINOLOGY ................................ 12 2 Seismic Dataset ..................................................................................................................... 15 2.1 SELECTION OF SEISMIC SURVEYS (2D and 3D) ................................................. 15 5 CR/16/041 Last modified: 2016/05/30 09:37 3 Seismic Interpretation ......................................................................................................... 20 3.1 SELECTED SEISMIC EVENTS ................................................................................. 20 3.2 WELL INFORMATION ................................................................................................ 33 3.3 SEISMIC CALIBRATION ............................................................................................. 34 3.4 CHALLENGES DURING THE INTERPRETATION ............................................... 35 3.5 SEISMIC INTERPRETATION ................................................................................... 35 4 Depth conversion method and generation of depth structure maps ................................... 44 4.1 INTRODUCTION ........................................................................................................ 44 4.2 KNOWN DIFFICULTIES IN DEPTH CONVERSION ............................................. 44 4.3 METHODOLOGY ....................................................................................................... 44 4.4 DEPTH CHECKING, RESIDUAL REDUCTION AND FINAL SURFACES .......... 51 5. Results ................................................................................................................................... 51 5.1 PRODUCTS ................................................................................................................. 52 5.2 DEPTH STRUCTURE MAPS FOR KEY HORIZONS ............................................. 52 5.3 ISOPACHS .................................................................................................................. 61 6 Conclusions and future work .................................................................................................. 62 References .................................................................................................................................... 63 FIGURES Figure 1 Focus of tasks in the Irish Sea Study Area ..................................................................... 10 Figure 2 Geographical coverage of previous work incorporated into this report. Background bedrock geology from BGS 1:250,000 offshore DigMap BGS©NERC (Jurassic-Triassic in pink-browns, Carboniferous in grey and blue). ................................................................. 12 Figure 3 Structural terminology used in this report, following Jackson and Mullholland