Reflection seismic thermometry A thesis submitted to The University of Manchester for the degree of Doctor of Philosophy in the Faculty of Science and Engineering 2020 Arka Dyuti Sarkar Department of Earth and Environmental Sciences TABLE OF CONTENTS TABLE OF CONTENTS.............................................................................................................. 2 LIST OF FIGURES ..................................................................................................................... 7 LIST OF TABLES..................................................................................................................... 10 LIST OF ABBREVIATIONS....................................................................................................... 11 ABSTRACT ............................................................................................................................ 13 DECLARATION ...................................................................................................................... 14 COPYRIGHT STATEMENT ...................................................................................................... 15 ACKNOWLEDGEMENT .......................................................................................................... 16 THESIS PRESENTATION ......................................................................................................... 18 1. Thesis overview................................................................................................................ 20 1.1 Why is subsurface temperature important? ............................................................... 20 1.2 Rationale .................................................................................................................... 21 1.3 References ................................................................................................................. 23 2. Thermal regime of sedimentary basins............................................................................. 25 2.1 Thermal structure of planet Earth .............................................................................. 25 2.1.1 Heat flow in the crust .......................................................................................... 30 2.2 Present state of knowledge ........................................................................................ 32 2.2.1 Thermal data measurement in upper crust .......................................................... 33 2.2.2 Heat flow databases ............................................................................................ 35 2.3 Approaches to determine thermal structure .............................................................. 40 2.3.1 Bottom Hole Temperatures ................................................................................. 41 2.3.2 ODP thermal measurement tools ........................................................................ 42 2.3.3 Indirect temperature indicators ........................................................................... 47 2 2.3.4 Deriving thermal conductivity .............................................................................. 48 2.4 Shallow geothermal gradient using gas hydrate stability conditions ........................... 59 2.4.1 Gas hydrates........................................................................................................ 59 2.4.2 Bottom simulating reflectors (BSRs) .................................................................... 73 2.5 Utilised dataset .......................................................................................................... 77 2.5.1 Case studies conducted ....................................................................................... 77 2.5.2 Data summary table ............................................................................................ 80 2.6 References ................................................................................................................. 81 3. Temperature from Seismic Reflection .............................................................................. 92 3.1 Abstract...................................................................................................................... 92 3.2 Introduction ........................................................................................................... 93 3.2.1 Geological setting ................................................................................................ 95 3.2.2 Gas Hydrates & Bottom Simulating Reflectors ..................................................... 98 3.2.3 Heat Flow ............................................................................................................ 99 3.2.4 Conventional thermal data ................................................................................ 101 3.3 Data ......................................................................................................................... 103 3.3.1 Seismic data ...................................................................................................... 103 3.3.2 Well data ........................................................................................................... 106 3.4 Method .................................................................................................................... 106 3.4.1 Thermal conductivity estimation ....................................................................... 109 3.4.2 Uncertainty modelling ....................................................................................... 114 3.5 Results ..................................................................................................................... 115 3.6 Discussion ................................................................................................................ 123 3.6.1 Uncertainty ....................................................................................................... 123 3.6.2 Implications ....................................................................................................... 125 3.7 Conclusions .............................................................................................................. 126 3.8 References ............................................................................................................... 126 3 4. Seismic characterization of thermal regime: a Blake Ridge study ................................... 134 4.1 Abstract.................................................................................................................... 135 4.1.1 Plain Language Summary ................................................................................... 135 4.1.2 Acronyms .......................................................................................................... 135 4.2 Introduction ............................................................................................................. 137 4.2.1 Geological setting .............................................................................................. 138 4.2.2 Gas hydrates and bottom simulating reflectors at the Blake Ridge .................... 139 4.2.3 Discrepancies in GHSZ ....................................................................................... 141 4.3 Materials and Methods ............................................................................................ 144 4.3.1 Shallow thermal regime ..................................................................................... 144 4.3.2 1D modelling of boreholes ................................................................................. 148 4.4 Data ......................................................................................................................... 151 4.4.1 Borehole data .................................................................................................... 152 4.4.2 Seismic data ...................................................................................................... 155 4.5 Results ..................................................................................................................... 158 4.5.1 Sensitivity analyses ............................................................................................ 158 4.5.2 Thermal modelling results contrasted: 3D & 1D modelling approaches ............. 159 4.6 Discussion ................................................................................................................ 166 4.7 Conclusions .............................................................................................................. 168 4.8 Acknowledgments, Samples, and Data ..................................................................... 169 4.9 References ............................................................................................................... 169 4.10 Appendix ................................................................................................................ 176 5. Subsurface temperature of the northern North Sea Basin .............................................. 179 5.1 Abstract.................................................................................................................... 179 5.2 Introduction ............................................................................................................. 181 5.2.1 Thermal modelling fundamentals .....................................................................