FACULTY OF SCIENCE AND TECHNOLOGY Department of Geology Origin and accumulation mechanism of shallow gas accumulations in the SW Barents Sea — Kristian Kjerkreit EOM-3901 Master’s Thesis in Energy, Climate and Environment June 2014 Abstract Events associated with shallow gas accumulations are reported all over the Norwegian continental shelf. These accumulations are potentially dangerous geo-hazards related to drilling activity, but they can also be of economic interest if the accumulated volumes are large. Petroleum in the Barents Sea has been influenced by the late periods of uplift and erosion creating a complex province. The exact distribution and formation mechanism of shallow gas accumulations have yet to better understood. This thesis focus on mapping the distribution of shallow gas accumulations located within the Tromsø Basin and adjacent areas in the SW Barents Sea. Data used consists mainly of publicly available 2D seismic data within the study area. 3D seismic data (surveys EL0001 and LN09M01) focus on specified amplitude anomalies associated with shallow gas accumulations, possibly linked with the formation of diagenesis-related BSR. Mapped seismic evidence of shallow gas is associated with bright spots, zones of acoustic masking and chaotic reflection pattern, chimneys and leakage along faults. The main stratigraphic units of this thesis are defined above Torsk fm., below Torsk fm. top and below Kolmule fm. and the upper Kolmule fm. Overall, the results give a general overview of the location of potential shallow gas accumulations. The general shallow gas origin is most likely of thermogenic generation from sources located at depths below the Kolmule fm. The source is most likely a mixture of source rocks, including the major Hekkingen fm. Major migration pathways within the study area bypass zones of deeper faulting, mainly the Ringvassøy-Loppa Fault Complex to the shallower levels. Migration pathways are also identified towards structural highs along the Tromsø basin border (Loppa High, Veslemøy High and Senja Ridge) and towards salt diapirs within central parts of the basin. Accumulation and migration occur mainly related to the interpreted intra Torsk fm. and below the sealing upper regional unconformity (URU). Accumulation mechanisms are related to structural and stratigraphic trapping and the development of traps associated with diapirs and BSR (both gas-hydrate and diagenesis- related BSR). I II Acknowledgements Først og fremst takk til min veileder førsteamanuensis Stefan Bünz som har gjort denne oppgaven mulig. Det har vært en spennende og lærerik prosess å skrive denne masteroppgaven. Takk til kontoret innerst i gangen i brakke sør og spesielt Espen Valberg. Vi har holdt sammen fra dag en. Alltid greit å ha noen i hjørnet som man kan rådføre seg med. Det ble mange flotte fussballmatcher, helt til spille ble ødelagt en uke før innleveringsfristen. Kanskje like greit? Vil også takke mine medstudenter på Energi, Klima og Miljø (kull ‘09). Det har vært mange fine stunder sammen her i Tromsø. Uansett om du er ferdig nå eller har noen år igjen, lykke til videre. Fem år som student ved Universitetet i Tromsø går nå mot slutten. Det har vært en krevende, men spennende periode. Tromsø har vært et fantastisk studiested, sommer som vinter. Skiturene har vært viktig for å koble av mellom de store slagene. Takk for alle turene. Takk til alle som var med. Takk til min familie som alltid har vært der for meg, uansett hva det skulle være. Til slutt vil jeg takke min kjære Astri. Du gjorde valg av studiested enkelt og har vært med meg igjennom hele studietiden. Nå går vi en spennende tid i møte, og jeg gleder meg virkelig til fortsettelsen! Kristian Kjerkreit Tromsø, Juni 2014 III IV “Det e bærre lækkert!” Potetbonde Olaf Sand V VI Table of Contents 1 INTRODUCTION........................................................................................................................................ 1 1.1 OBJECTIVE ................................................................................................................................................. 1 1.2 MOTIVATION ............................................................................................................................................. 1 1.3 SHALLOW GAS ........................................................................................................................................... 2 1.3.1 Generation ......................................................................................................................................... 3 1.3.2 Migration ........................................................................................................................................... 4 1.3.3 Accumulation..................................................................................................................................... 5 1.4 SEISMIC INDICATIONS OF HYDROCARBONS ....................................................................................................... 7 1.4.1 Seismic Response ............................................................................................................................... 8 1.5 BOTTOM-SIMULATING REFLECTORS (BSR) .................................................................................................... 10 1.5.1 Gas-Hydrate Related BSR ................................................................................................................ 10 1.5.2 Diagenesis-Related BSR ................................................................................................................... 10 1.6 AMPLITUDE ANOMALY PITFALLS .................................................................................................................. 12 1.7 SEISMIC RESOLUTION ................................................................................................................................ 12 2 STUDY AREA .......................................................................................................................................... 13 2.1 BARENTS SEA ........................................................................................................................................... 13 2.1.1 Geological Provinces........................................................................................................................ 15 2.1.2 Nomenclature and Stratigraphy ...................................................................................................... 16 2.1.3 Uplift and Erosion ............................................................................................................................ 18 2.1.4 Source Rock ..................................................................................................................................... 20 2.1.5 Geological Plays .............................................................................................................................. 20 2.2 TROMSØ BASIN ........................................................................................................................................ 21 2.2.1 Geographical Location..................................................................................................................... 21 2.2.2 Development and Evolution ............................................................................................................ 21 2.2.3 Well Data ......................................................................................................................................... 25 3 METHODS AND DATA ............................................................................................................................ 29 3.1 DEFINITION AND IDENTIFICATION OF SHALLOW GAS ACCUMULATIONS ................................................................ 29 3.2 SEISMIC DATA .......................................................................................................................................... 30 3.2.1 2D Seismic Data ............................................................................................................................... 30 3.2.2 3D Seismic Data ............................................................................................................................... 31 3.3 INTERPRETATION AND VISUALIZATION TOOLS ................................................................................................. 32 3.3.1 Petrel Software ................................................................................................................................ 32 4 RESULTS ................................................................................................................................................. 35 4.1 QUALITY OF SEISMIC DATA ......................................................................................................................... 36 4.2 IDENTIFICATION OF SHALLOW GAS ACCUMULATIONS ....................................................................................... 36 4.3 INTERPRETATION PITFALLS .......................................................................................................................... 41 4.4 DISTRIBUTION OF SHALLOW GAS ACCUMULATIONS ......................................................................................... 43 4.4.1 Above Torsk fm. ............................................................................................................................... 43 4.4.2 Below Torsk fm. top and Above Kolmule fm.................................................................................... 44 4.4.3 Upper Kolmule fm. ........................................................................................................................... 45 4.4.4 Deep Source Features ...................................................................................................................... 46 4.4.5 Flat and Dipping Reflections ............................................................................................................ 46 4.4.6 Salt Diapirs and Structural Highs ..................................................................................................... 48 4.5 INTERPRETATION OF 3D DATA .................................................................................................................... 48 4.5.1 EL0001 ............................................................................................................................................. 49 VII 4.5.2 LN09M01 ......................................................................................................................................... 49 4.5.3 3D Features Extent .......................................................................................................................... 52 5 DISCUSSION ........................................................................................................................................... 55 5.1 SEISMIC QUALITY ...................................................................................................................................... 56 5.2 SEISMIC EVIDENCE OF SHALLOW GAS ........................................................................................................... 56 5.3 IDENTIFICATION OF SHALLOW GAS ACCUMULATIONS ....................................................................................... 57 5.4 DISTRIBUTION OF AMPLITUDE ANOMALIES RELATED TO SHALLOW GAS ACCUMULATIONS ...................................... 59 5.4.1 Stratigraphic Boundaries ................................................................................................................. 60 5.4.2 Structural Boundaries ...................................................................................................................... 60 5.4.3 Lateral Extent of 3D Features .......................................................................................................... 61 5.5 HYDROCARBON ACCUMULATION INTERVALS .................................................................................................. 61 5.5.1 Above Torsk fm. ............................................................................................................................... 62 5.5.2 Below Torsk fm. top and Above Kolmule fm.................................................................................... 62 5.5.3 Below Kolmule fm. top .................................................................................................................... 62 5.5.4 General Trend .................................................................................................................................. 63 5.6 COMBINATION OF DISTRIBUTION MAPS ........................................................................................................ 63 5.7 SHALLOW GAS ORIGIN AND GENERATION ..................................................................................................... 65 5.8 3D SEISMIC FEATURES OF INTEREST ............................................................................................................. 66 5.8.1 EL0001 Feature ................................................................................................................................ 67 5.8.2 LN09M01 Feature ............................................................................................................................ 68 5.8.3 3D Seismic Features Extent ............................................................................................................. 68 5.9 FLUID MIGRATION .................................................................................................................................... 69 5.10 ACCUMULATION MECHANISM ..................................................................................................................... 76 5.10.1 Shallow Gas Related to BSR ........................................................................................................ 76 5.10.2 Salt Diapirs and Structural Highs ................................................................................................ 79 5.10.3 Stratigraphic Trapping ................................................................................................................ 81 5.11 GENERATION, MIGRATION AND ACCUMULATION; TROMSØ BASIN AND ADJACENT AREAS. ..................................... 83 6 CONCLUSION ......................................................................................................................................... 87 7 REFERENCES ........................................................................................................................................... 89 VIII