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Shallow gas: A shallow or a deep problem?

Workshop on Cable-based Ocean Observatories 12 June 2007 Hotel Norge, Bergen Instrumentation at Troll ( as considered relevant for seabed observatories) by Tor Inge Tjelta, Statoil based on papers 18699 and 18706, OTC, Houston 1 st May 2007. Shallow gas: A shallow or a deep problem?.

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Shallow gas: A shallow or a deep problem?

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  1. Workshop on Cable-based Ocean Observatories12 June 2007 Hotel Norge, Bergen Instrumentation at Troll (as considered relevant for seabed observatories)by Tor Inge Tjelta, Statoil based on papers 18699 and 18706, OTC, Houston 1st May 2007

  2. Shallow gas: A shallow or a deep problem?

  3. Concerns Coupled mechanisms Wells Foundation Source Hazards Gas seepage from ? High pressures (1-15 bar) Large volumes Seepage? From where? reservoar

  4. P I M O Source? dC13 1 - 6 bar 30 - 35 moh ? density? ? Source? dC13 dC13 P? P? Temperature? d oC Main focus areas (Troll Shallow Gas Project) 300 m Pockmark Observation well 0 m -200 m

  5. Pockmarks, what/when/how?

  6. Example of investigations at Septagram pockmark Coring, BAT, CPT and piezometers + lab

  7. Pockmark study – multilevel piezometer Red: temperature Blue: excess pore pressure PZM101: Failed installation PZM102: Basin PZM 103: Flank

  8. Carbonates and corals in the base of the pockmarks

  9. Gas migration in seabed and pockmarks No sedimentation in PMFluid seepage?Bottom currents? 0m Today 2m 10000ybp Fluid (gas or water) Carbonate 11m Zero gas today! Active pockmark ( 85% - 90%)

  10. Instrumented smart well, close to platform. Will be permanently connected to Troll A. An opportunity? Observation well

  11. Gas is seeping into well annulus at constant rate Pressure is a result of gas seepage into the annulus Gas source is local Hydrogen plays a role! Gas Gas Gas ? 20” ~15ºC ? ? 14” ~ 45ºC ? ? 10¾” ~60ºC Gas seepage

  12. Conclusions • Observed gas and pressures do not have an impact on platform integrity and safety • Mitigation • Handling gas and pressures by standard methods • Monitoring strategy • Gas seepage is a generic well problem in oil and gas production • Cement is not an efficient seepage barrier • Pockmarks at Troll are seepage made but not very active today

  13. An observatory inside a pockmark?

  14. Monitoring of the marine environmentCable-based sea bed observatories • Statoil is considering the possibilities for connection to existing and future subsea infrastructure: - provide specific locations for cabled seabed observatories (present and future Statoil operated fields) - Pilot: Troll A? • Gain:- Better understand the nature and variation to marine ecosystems in areas of interest- Knowledge about impacts resulting from influenceother than our planned activities (climate change, other pollutants etc.)- Monitor parameters of local importance for the selectedfield (gas hydrates, natural seeps)

  15. Monitoring of environmental parameters • Deployment of nodesRecording data to monitor global, regional and local environmental parameters in a long time perspective • Physical/chemical parameters: - Temperature - Salinity - Deep-water currents • Ecosystem/biological parameters: - Biodiversity - Biological resources (fish and plankton)- Spawning products

  16. Scientific initiativesNEPTUNE & ESONET • Developing a network of seabed observatories to monitor global, regional and local environmental parameters in a longtime perspective - NEPTUNE: installing a 380 km cable system from shore - ESONET: in addition consider connection to existing/future subsea infrastructure • Gain experience from NEPTUNE and ESONET

  17. ESONET • European initiative, with participants from HERMES, to build cable-based ocean observatories in the HERMES area – from Arctic via the Mediterranean Sea to the Black Sea • Continuous long-term measurement of environmental data for monitoring of climate changes etc. • App. 5000 km fibre optic sea cables linking observatories to the land via junction box terminations on the sea floor. ESONET:European Sea Floor Observatory Network

  18. HERMES • EU funded research program: - Aim to develop concepts and trategies for the sustainable use of marine resources - Gain a comprehensive understanding of the different deep-sea ecosystems and how they work - From Arctic to Black Sea • Ambitious multidisciplinary crusie program collecting deep-sea data- Cold-water coral reefs, cold seeps,canyon systems HERMES: Hotspot Ecosystems Research on the Margins of European Seas

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