Gas Hydrates in the Brazilian Continental Margin: Inferred Occurrences and Current Investigations

1. Gas Hydrates in the Brazilian Continental Margin: Inferred Occurrences and Current Investigations Dennis J. Miller PETROBRAS - CENPES November 28, 2008 www.ess.nrcan.gc.ca www.oceanexplorer.noaa.gov

2. Gas Hydrates in the Brazilian Continental Margin: Inferred Occurrences and Current Investigations • Presentation outline: • Definition • Characteristics • Associated features in seismic records • Potential as an energy source • Inferred occurrences in Brazil • Current investigations in Brazil • Conclusions

3. Definition – What are gas hydrates? Gas hydrates are compounds occurring in nature as crystalline solids in the form of ice, where gas molecules (guest) are trapped by a lattice of water molecules (hosts), forming cage-like structures known as clathrates. Common examples are methane hydrates and CO2 hydrates. They are found in nature below the permafrost in polar regions and in marine or lacustrine sediments in water depths generally exceeding 450 / 500 meters. Hardage e Roberts, 2006 www.esemag.com

4. Characteristics – chemical structures Gas hydrates occur in three different chemical structures. Sloan, 2003

5. Characteristics – conditions for formation Gas hydrates require specific conditions for their formation: - High pressure - Low temperature - High gas concentration The gas will dissociate from the water once these conditions are not met. Gas hydrate phase stability diagram. Hypothetical case – seafloor at 1200 m water depth. Burning gas hydrate. www.steacie.nrc-cnrc.gc.ca www.netl.doe.gov

6. Characteristics – different morphologies Nodules, lenses, layers or laminations (muddy sediments). Filling oblique and sub-vertical fractures (muddy sediments). Tomography image Length = 90 cm Saeki, 2008 In section Disseminated (sands). Saeki, 2008 Holland, 2008

7. Characteristics – types of deposits • Walsh (2008) classifies gas hydrate deposits into four types: • Type 1: hydrate deposits over free gas. • Type 2: hydrate deposits over water. • Type 3: hydrate deposits over no mobile fluids. • Type 4: localized and dispersed deposits on the seafloor. • Only types 1 and 2 are exploitable with current technology.

8. Characteristics – potential uses • Gas hydrates can have the following potential uses: • Energy source. • Gas storage and transport. • Geologic storage of CO2. • Hydrogen storage. • Seawater desalinization. • Refrigerating systems.

9. Gas hydrate Seismic velocity Gas hydrate stability curve Seafloor Grains Pore water Gas hydrate stability zone Free gas zone Free gas Geothermal gradient Associated features in seismic records The ocurrence of gas hydrates is generally associated to specific features in seismic records. BSRs (Bottom Simulating Reflectors) are considered the most diagnostic. Other related features are: gas chimneys, acoustic blanking and turbidity, high amplitude reflectors mounds, pockmarks, and acoustic plumes in the water column. Adapted from Clennell, 2000

10. Associated features in seismic records Seismic section from the Canadian continental margin displaying a BSR. Mosher, 2008

11. Associated features in seismic records • Some observations regarding BSRs: • Gas hydrates are not always present where BSRs are observed in seismic records. • Gas hydrates can be present where BSRs are weak or absent. • Berndt et al. (2004) have shown that similar BSR features can also occur where diagenetic transformations from opal-C to opal-AT and from smectite to illite have taken place and where large amounts of authigenic carbonate have deposited. Mosher, 2008

12. Potential as an energy source • - According to Sloan (2003), the great energy potential of gas hydrates derives from the fact that one volume of gas hydrates with total occupancy of guest cavities corresponds to 180 volumes of gas at surface conditions. • Some authors estimate that gas hydrates may contain more than twice the amount of energy than all other fossil fuels combined. • However, recent estimates indicate varying recoverable volumes depending on the type of reservoir and the geological setting where it occurs.

13. Potential as an energy source Estimated gas volumes from gas hydrates and other sources. Boswell e Collett, 2006

14. Potential as an energy source – production from permafrost Production tests carried out in Mallik 2L-38 e Mallik 5L-38 wells (NW Canada) in 2007 e 2008, respectively, using depressurization. Well with test assembly Sandy reservoir: nearly 30 meters Test in 2007: 830 m3 in 15 hours. Test in 2008: 840 m3 in nearly six days. Dallimore, 2008 Numasawa, 2008

15. Potential as an energy source – production from deepwater sands • Production tests are expected within the next five years in deepwater turbidite sands in the Nankai Trough, east of Japan. In place gas volumes are estimated in 20 tcf (Fujii et al.,2008).

16. Potential as an energy source • Challenges: • Slow dissociation, relatively low production. • Significant water and sand or mud production from relatively unconsolidated reservoirs. • Horizontal dissociation front (horizontal wells not as effective). • Secondary hydrate formation in the well and production lines. • Well instability. • Overburden collapse.

17. Inferred occurrences in Brazil - BSR Rio Grande Cone – Pelotas Basin Area ~ 45,000 km2 Bathymetry – from ~ 500 to 3,500 m Estimated volume ~ 780 TCF (Sad et al., 1998)

18. Inferred occurrences in Brazil BSR at the Rio Grande Cone Upper to middle continental slope.

19. Inferred occurrences in Brazil BSR at the Rio Grande Cone Mid to lower continental slope.

20. Inferred occurrences in Brazil BSR at the Rio Grande Cone Continental Rise below the thrust and fold belt.

21. Amazon Cone – Foz do Amazonas Basin Area ~ 28,000 km2 Bathymetry – from ~ 600 to 2,800 m Estimated volume ~ 430 TCF Inferred occurrences in Brazil - BSR (Sad et al., 1998)

22. Inferred occurrences in Brazil BSR at the Amazon Cone Thrust and fold belt. BSR

23. Inferred occurrences in Brazil BSR at the Amazon Cone Thrust and fold belt. BSR

24. SW NE Inferred occurrences in Brazil BSR at the Amazon Cone Thrust and fold belt.

25. Inferred occurrences in Brazil - BSR Other BSRs along the Brazilian continental margin.

26. Potential settings in Brazil for future gas hydrate investigations Other areas in the Brazilian continental margin to be investigated for gas hydrate accumulations: Jequitinhonha River delta – BA Parnaíba River delta - PI São Francisco River delta – SE/AL Ab’Saber, 2003 Doce River delta – ES GoogleEarth Ab’Saber, 2003 Ab’Saber, 2003 Strahler, 1981

27. Occurrences in Africa – BSR isopach at the Niger Delta. Cunningham and Lindholm, 2000

28. Occurrences in Africa – BSR in seismic line from the Niger Delta. Cunningham and Lindholm, 2000

29. Occurrences in Africa – BSR isopach at the Congo slope. Cunningham and Lindholm, 2000

30. Occurrences in Africa – BSR in seismic line from the Congo slope. Cunningham and Lindholm, 2000

31. Current investigations in Brazil Several activities are being conducted in Brazil with the purpose of investigating gas hydrates: PETROBRAS: - R&D project: presently reprocessing 2-D seismic lines. Next steps include geophysical studies (seismic attributes, inversion, etc.), new data acquisition (seismic and CSEM), modeling and drilling favorable sites. - Within the project cooperative research agreements are underway or being discussed with: University of Tokyo (Japan), CSIRO (Australia), NOC Forum and PUC-RS/OGS-Trieste (Italy). Other institutions: - ANP/UFRGS and UFF-LAGEMAR.

32. Conclusions • Gas hydrates occur in a variety of geological settings, reservoirs, types of deposits and morphologies. Their correct identification through seismic (BSRs) is not always accurate. Therefore quantification of gas volumes associated to gas hydrate accumulations is a complex task. • Further technological development will be necessary to produce from gas hydrates in an economically feasible manner. • The southern and equatorial Atlantic have large areas with clear seismic features which can potentially be related to gas hydrate deposits. A significant effort will be necessary to characterize these deposits and test their potential as an energy source (challenge).

33. Seismic line from the Pelotas Basin processed using the VA Technique (Petrobras). www.soundwaves.usgs.gov

34. Thank you for your attention.