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

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

Investigations

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

Investigations

November 28, 2008November 28, 2008

Dennis J. MillerDennis J. Miller

www.oceanexplorer.noaa.govwww.ess.nrcan.gc.ca

PETROBRAS - CENPESPETROBRAS - CENPES

Presentation outline:

• Definition

• Characteristics

• Associated features in seismic records

• Potential as an energy source

• Inferred occurrences in Brazil

• Current investigations in Brazil

• Conclusions

Presentation outline:

• Definition

• Characteristics

• Associated features in seismic records

• Potential as an energy source

• Inferred occurrences in Brazil

• Current investigations in Brazil

• Conclusions

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

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

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.

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.

Definition – What are gas hydrates?Definition – What are gas 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.

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

Gas hydrates occur in three different chemical structures.Gas hydrates occur in three different chemical structures.

Characteristics – chemical structuresCharacteristics – chemical structures

Sloan, 2003

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 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.

Gas hydrate phase stability diagram. Hypothetical case – seafloor at 1200 m water depth.

www.steacie.nrc-cnrc.gc.ca

Burning gas hydrate.Burning gas hydrate.

www.netl.doe.gov

Characteristics – conditions for formationCharacteristics – conditions for formation

Holland, 2008 Saeki, 2008

Saeki, 2008

Filling oblique and sub-vertical fractures (muddy sediments).

Filling oblique and sub-vertical fractures (muddy sediments).

Tomography image

Length = 90 cm

Tomography image

Length = 90 cm

In sectionIn section

Nodules, lenses, layers or laminations (muddy sediments).

Nodules, lenses, layers or laminations (muddy sediments).

Disseminated (sands).Disseminated (sands).

Characteristics – different morphologiesCharacteristics – different morphologies

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.

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.

Characteristics – types of depositsCharacteristics – types of deposits

Gas hydrates can have the following potential uses:

- Energy source.

- Gas storage and transport.

- Geologic storage of CO2.

- Hydrogen storage.

- Seawater desalinization.

- Refrigerating systems.

Gas hydrates can have the following potential uses:

- Energy source.

- Gas storage and transport.

- Geologic storage of CO2.

- Hydrogen storage.

- Seawater desalinization.

- Refrigerating systems.

Characteristics – potential usesCharacteristics – potential uses

The ocurrence of gas hydrates is generally associated to specific features in seismic records. BSRs (Bottom Simulating Reflectors) are considered the most diagnostic.

The ocurrence of gas hydrates is generally associated to specific features in seismic records. BSRs (Bottom Simulating Reflectors) are considered the most diagnostic.

Associated features in seismic recordsAssociated features in seismic records

Adapted from Clennell, 2000

Other related features are: gas chimneys, acoustic blanking and turbidity, high amplitude reflectors mounds, pockmarks, and acoustic plumes in the water column.

Other related features are: gas chimneys, acoustic blanking and turbidity, high amplitude reflectors mounds, pockmarks, and acoustic plumes in the water column.

Gas hydrate stability curve

Gas hydrate stability zone

Free gas zone

Seafloor

Seismic velocity

Geothermal gradientFree gas

Grains Porewater

Gas hydrate

Mosher, 2008

Seismic section from the Canadian continental margin displaying a BSR.Seismic section from the Canadian continental margin displaying a BSR.


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.

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


Potential as an energy sourcePotential 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.

- 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.

Boswell e Collett, 2006

Estimated gas volumes from gas hydrates and other sources.Estimated gas volumes from gas hydrates and other sources.


Dallimore, 2008

Numasawa, 2008

Production tests carried out in Mallik 2L-38 e Mallik 5L-38 wells (NW Canada) in 2007 e 2008, respectively, using depressurization.Production tests carried out in Mallik 2L-38 e Mallik 5L-38 wells (NW Canada) in 2007 e 2008, respectively, using depressurization.

Test in 2007: 830 m3 in 15 hours.

Test in 2008: 840 m3 in nearly six days.

Test in 2007: 830 m3 in 15 hours.

Test in 2008: 840 m3 in nearly six days.

Well with test assemblyWell with test assembly

Sandy reservoir: nearly 30 metersSandy reservoir: nearly 30 meters

Potential as an energy source – production from permafrost

Potential as an energy source – production from permafrost

- 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).

- 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).

Potential as an energy source – production from deepwater sands

Potential as an energy source – production from deepwater sands

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.

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.


Rio Grande Cone – Pelotas Basin Area ~ 45,000 km2

Bathymetry – from ~ 500 to 3,500 mEstimated volume ~ 780 TCF

Inferred occurrences in Brazil - BSRInferred occurrences in Brazil - BSR

(Sad et al., 1998)

Inferred occurrences in BrazilBSR at the Rio Grande Cone


Upper to middle continental slope.Upper to middle continental slope.



Mid to lower continental slope.Mid to lower continental slope.

Continental Rise below the thrust and fold belt.Continental Rise below the thrust and fold belt.



Amazon Cone – Foz do Amazonas BasinArea ~ 28,000 km2

Bathymetry – from ~ 600 to 2,800 mEstimated volume ~ 430 TCF

(Sad et al., 1998)


BSR

Inferred occurrences in BrazilBSR at the Amazon Cone


Thrust and fold belt.

BSR




SW NE




Other BSRs along the Brazilian continental margin.Other BSRs along the Brazilian continental margin.


Other areas in the Brazilian continental margin to be investigated for gas hydrate accumulations:Other areas in the Brazilian continental margin to be investigated for gas hydrate accumulations:

Potential settings in Brazil for future gas hydrate investigationsPotential settings in Brazil for future gas hydrate investigations

Parnaíba River delta - PIParnaíba River delta - PI São Francisco River delta – SE/ALSão Francisco River delta – SE/AL

Jequitinhonha River delta – BAJequitinhonha River delta – BA

Doce River delta – ESDoce River delta – ES

GoogleEarth Ab’Saber, 2003

Ab’Saber, 2003

Ab’Saber, 2003Strahler, 1981

Occurrences in Africa – BSR isopach at the Niger Delta.Occurrences in Africa – BSR isopach at the Niger Delta.

Cunningham and Lindholm, 2000

Occurrences in Africa – BSR in seismic line from the Niger Delta.Occurrences in Africa – BSR in seismic line from the Niger Delta.


Occurrences in Africa – BSR isopach at the Congo slope.Occurrences in Africa – BSR isopach at the Congo slope.


Occurrences in Africa – BSR in seismic line from the Congo slope.Occurrences in Africa – BSR in seismic line from the Congo slope.


Current investigations in BrazilCurrent 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.

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.

ConclusionsConclusions

- 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).

- 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).

www.soundwaves.usgs.gov

Seismic line from the Pelotas Basin processed using the VA Technique (Petrobras).Seismic line from the Pelotas Basin processed using the VA Technique (Petrobras).

Thank you for your attention.Thank you for your attention.

Documents

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