Fire in Ice Milkov

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Gas Hydrate Resource Potentialin the Gulf of Mexico

Alexei V. Milkov

BP America, Houston TX

This work has been done at Texas A&M University and

Woods Hole Oceanographic Institution.

The presented interpretations and ideas do not

necessarily reflect the viewpoint of BP.



U.S. natural gas demand and supply

Provided by DOE



What is gas hydrate?

Pictures provided by ODP, GEOMAR, A.V. Milkov, and R.Sassen



Global distribution of gas hydrates

After Milkov and Sassen, 2002



Global submarine gas hydrate estimates

Milkov (in press, Earth-Science Reviews)

Kvenvolden

(1988)ODP 164

ODP 204



Looking for trends




Organic carbon in the Earth

Kvenvolden, 1988




Gas hydrates in the Gulf of Mexico

Modified from Milkov and Sassen, 2003 (bathymetry courtesy of Dr. W.Bryant)



Conceptual model for gas hydrate occurrence

0

2

4

6

8

10

12

14

16

18

20

22

Abyssalplain

Sigsbee ScarpShelfIsolated

stocks

Minibasin

D e p t h ,

k m

Area of gas hydrate occurrence

SaltBacterial methanehydrates in minibasins

Bacterial and thermogenicstructurally-focused gas hydrates

Milkov and Sassen, 2001

G l i l ifi i f h d



Geologic classification of gas hydrateaccumulations

Gulf of Mexico

Hydrate Ridge(southern summit)

Blake Ridge

Nankai Trough(???)

Haakon Mosby

mud volcano

Caspian Sea

Blake Ridge(???)




Origin of gas hydrates

Data from Paull et al., 2000 and Sassen et al., 1999



Area of gas hydrate resource estimation

Gas hydrates, seeps, and fields after Sassen et al., 1999



Data and assumptions (1)

• Gas availability and composition (%)

Sample C1 C2 C3 i-C4 n-C4 i-C5 n-C5

1 100 0 0 0 0 0 0

2 95.9 2.4 1.2 <0.1 0.3 0.2 <0.1

3 90.4 4.5 3.7 0.6 0.6 0.2 <0.1

Data after Sassen et al., 1999



Data and assumptions (2)• Pore water salinity - 35 g/l

• Hydrostatic pressure gradient - 10 MPa/km

• The effect of porous media is not considered

Sloan’s (1998) CSMHYD Hydrate Program was used



Bathymetry of the study area

East Breaks

Alaminos Canyon Keathley Canyon

Garden Banks

Walker Ridge Lund

Atwater

MississippiCanyon

50 km Green Canyon

2 1 0 0

7 0 0

9 0 0

1 1 0 0

1 3 0 0

1 5 0 0

1 7 0 0

1 9 0 0

7 0 09 0 0

1 1 0 0

1 3 0 0

7 0 0

9 0 0

1 1 0 0 1 3 0

0

1 5 0 0

1 9 0

0

9 0 0

7 0 0

Shallow thermogenic gas hydrate

Oil and gas seeps with chemosynthetic communities

Shallow and deep biogenic gas hydrate

Boundary of the gas hydrate resource estimation area7 0 0

Bathymetry contour lines

After Bryant et al., 1990



Bottom water temperature vs. water

depth in the study area

T = 295.08xB-0.5727

R2 = 0.9664

25

20

15

10

5

00 1000 2000 3000

Water depth (B), m

W a t e r t e m

p e r a t u r e ( T ) , 0 C

Data after Wash et al., 1998



Geothermal gradients in the study area

East Breaks


Garden Banks

Walker Ridge

Green Canyon

Lund

Atwater

Mississippi

Canyon

50 km

34.123.7 19.3

30.6

18.1 18.1 18.3

20.9

18.8

23.618.5

22.0 24.2 20.6

27.7

21.7 23.0

18.125.4

22.1

30.1

17.0

20.0

8.0

Geothermal gradients calculated from BHT

Boundary of the gas hydrate resource estimation area

Geothermal gradients calculated from heat flow measurements

Data courtesy of MMS and from Epp et al. (1970)



Geothermal gradients vs. water depth

in the study area

G = -9.6092xLn(B) + 88.4

R2 = 0.5917

25

20

15

10

5

0 1000 2000 3000

Water depth (B), m

G e o t h e r m a l g r a d i e n t ( G ) , o C / k m

30

35

40

Data courtesy of MMS and from Epp et al. (1970)



Gas hydrate stability conditions

25

20

15

10

5

00 1000 2000 3000

Depth (D), m

T e m p

e r a t u r e ( T s t

) , 0 C

Tst_90.4 = 6.6877xLn(D) - 27.637

R2 = 0.9942

Tst_95.9 = 7.1458xLn(D) - 33.908

R2 = 0.9963

Tst_100 = 8.9449xLn(D) - 50.148

R2 = 0.9991

30

4000

100% CH4:

95.9% CH4:

90.4% CH4:

Calculated using Sloan’s (1998) CSMHYD Hydrate Program

G h d bili



Gas hydrate stability zones vs.

water depth in the study area




Thickness of the methane GHSZ

East Breaks


Garden Banks

Walker Ridge Lund

Atwater

MississippiCanyon

50 kmGreen Canyon


Thickness of GHSZ (100% CH4) contour lines

2 0 0

2 0 0

0

4 0 0

6 0 0

1 0 0 0

800

1 2 0 0

0

2 0 0

400 6 0

0

8 0 0

1 0 0 0

2 0 0

0 4 0 0




Thickness of the thermogenic

(95.9% C1) GHSZ

East Breaks


Garden Banks

Walker Ridge Lund

Atwater

MississippiCanyon

50 km Green Canyon


Thickness of GHSZ (95.9% CH4) contour lines

1 0 00

1 2 0 0

1 2 0 0

6 0 0

8 0 0

2 0 0

400

2 0 0

2 0 0

6 0 0

8 0 0

1 0 0

0

400

2 0 0

4 0 0

6 0 0

8 0 0




Thickness of the thermogenic

(90.4% C1) GHSZ

3 0 0

500

7 0 0

9 0 0

5 0 07 0 0

9 0 0

1 1 0 0

1 3 0 0

1 5 0 0

5 0 0

7 0 0

3 0 0

9 0 0

110 0

1 3 0 0

1 5 0 0

East Breaks


Garden Banks

Walker Ridge Lund

Atwater

MississippiCanyon

50 kmGreen Canyon


Thickness of GHSZ (90.4% CH4) contour lines




Salt distribution map

50 kmEast Breaks


Garden Banks

Walker Ridge

Atwater

Mississippi

Canyon

Green Canyon


Top salt less than 1.0 sec subseafloor

Top salt 1.0 - 2.0 sec subseafloor

Top salt 2.0 - 4.0 sec subseafloor

Top salt >4.0 sec subseafloor




After Watkins et al., 1996

Mi ib i



Minibasin geometry map

East Breaks

Alaminos Canyon Keatley Canyon

Garden Banks

Walker Ridge Lund

Atwater

Mississippi

Canyon

50 km

Green Canyon

Minibasins

Allochthonous salt




Mississippi Fan


Compiled from Koch et al., 1998 and Risch, 1995

St t ll f d h d t



Structurally-focused gas hydrate

between minibasins• The total volume of the GHSZ between minibasins:

- ~12,000 km3 for 95.9 % of C1

- ~16,000 km3 for 90.4 % of C1

• Gas hydrate saturation: 0.5 vol.% of sediments

• Gas hydrate yield: 140 m3 of gas per 1 m3 of gas hydrate at STP

8-11 x 1012 m3 (280-390 TCF) at STP

(methane + C2+ hydrocarbon gases)



Gas hydrate in minibasins

• The total volume of the GHSZ between minibasins:

- ~12,000 km3 excluding Mississippi Fan

- ~17,000 km3 including Mississippi Fan

• Gas hydrate saturation: 0.1 vol.% of sediments

• Gas hydrate yield: 150 m3 of gas per 1 m3 of gas hydrate at STP

2-3 x 1012 m3 (70-105 TCF) of methane at STP



Summary of GoM regional estimation

• Combined estimate of the gas hydrate resource in the Gulf ranges from 10 to 14 trillion m3 (~350-495 TCF) :

- Significantly less than previous (Collett, 1995) estimate;

- ~ 30-40 times more gas than in conventionalreservoirs.

• Bacterial gas hydrate in minibasins is disseminated and noteconomically significant.

• Structurally-focused gas hydrate accumulations are

economically viable and should be a priority for further researchin the GoM.

See Milkov and Sassen (2001, Marine Geology) for details

Estimates of hydrate bound gas in



Estimates of hydrate-bound gas in

individual accumulations

Oil&Gas Journal., 1999

Seismic



Seismic

profiles acrossgas hydrate

accumulations Lee, 1995

Lee, 1995

Sager and Kennicutt, 2000

S b i h d t t bilit



Submarine gas hydrate stability zone

Bottom water temperature

Geothermal gradient

Pressure

Pore water salinity

Gas composition


Southern summit of Hydrate Ridge



Juan de Fucaplate

B l a n c o T r a n s f o r m

Mendocino Transform

Gordaplate

Explorerplate

Oregon

HydrateRidge

North Americanplate

Southern summit of Hydrate Ridge

• A poor but the only availabledrilled analogue for GoM high-flux

accumulations?

• Southern summit: high seafloor

reflectivity, gas vents, exposed gashydrate, and a chemosynthetic

community surrounding a 50-m-

high carbonate pinnacle

• Sites 1249 and 1250 lie beneath778–796 m of water

• A strong BSR at ~110-115 mbsf

• Brine (>106 g kg-1) present in

shallow sediments• Gas hydrate was sampled and

inferred to occur throughout the

section

But what are theconcentrations???

Images from Tréhu et al., 2002

ODP Pressure Core Sampler



p

• PCS is a downhole tool developed at

ODP (Pettigrew, 1992) to samplemarine sediments under in situpressure (up to ~70 MPa).

• If the recovered sediment core is notpressurized, about 99% of gas may belost (Paull and Ussler, 2001). Thus,the PCS is a great tool to measure the

in situ concentration of natural gases.• Data obtained from the PCS degassing

experiments and properly analyzed

may be used to estimate gas and gashydrate concentration in situ.

• PCS has been successfully used onLegs 164, 201, and 204.

Milkov et al., 2003

Volume of hydrate bound gas



Volume of hydrate-bound gas

• Gas hydrate concentrations at

Sites 1249 and 1250:

~1% to 43% of porosity (average

~11%) above the BSR (all corestaken)

• Area: 0.19 km2 (high seafloor

reflectivity)

• Thickness of the hydrate-bearingsediments: 115 m

• Gas yield of hydrate-bearing

sediments: ~13.5 m3 /m3

Images from Tréhu et al., 2002

V=VGHZ

×D = 0.19×106 m3 ×115m × 13.5 m3 /m3=

= ~3 ×108 m3 = ~0.01 tcf See Milkov et al. (2003, Geology) for details

Gas hydrate concentrations



Gas hydrate concentrations

Hydrate Ridge offshore OR(summit = high gas flux setting)

Chen and Cathles, 2003


Gulf of Mexico

Milkov et al., 2003

Green Canyon (GC) 184/185) )



Green Canyon (GC) 184/185

Water depth: 540-650 mArea:

Bush Hill mound – 101,300 m2

Hazy reflections – 350,700 m2

GHSZ:

Thickness – 370-390 m

Volume – 0.175×109

m3

GH concentration: 1-10%

GH composition: 77.5% C1

Volume of gas: (0.5-1.6)×109

m3

0.017-0.056 tcf

M i l k o v a n d S a s s e n ,

2 0 0 3

( b a s e d o n N e u r a u t e r

a n d B r y a n t (

1 9 9 0 ) , C o o k

a n d D ’ O n f r o

( 1 9 9 1 )

Major uncertainty:

Gas hydrate distribution

Mississippi Canyon (MC) 852/853




Water depth: 1080-1120 mArea: 1,935,500 m2

GHSZ:

Thickness – 780 m

Volume – 1.5×109 m3



Volume of gas:

(11.4-22.7)×109 m3

0.4-0.8 tcf M

i l k o v a n d S a s s e n , 2

0 0 3

( b a s e d o n S a g e r a n

d K e n n i c u t t ( 2 0 0 0 ) a n d p r o p r i e t a r y d a t a )

Major uncertainty: GHSZ

Effect of migrating brines?

Green Canyon (GC) 204



Green Canyon (GC) 204

M i l k o v a n d S

a s s e n , 2 0 0 3

( b a s e d o n B r o

o k s e t a l . ( 1 9

8 6 ) , S a s s e n e

t a l . ( 2 0 0 3 ) ) Water depth: 850-1000 m

Area: 26,131,000 m2

GHSZ:

Thickness – 640 m

Volume – 16.7×109 m3



Volume of gas:

(25.1-126)×109 m3

0.9-4.5 tcf

Major uncertainty:Gas hydrate distribution

Atwater Valley (AT) 425/426



Atwater Valley (AT) 425/426

Water depth: 1920-1940 mArea: 5,650,000 m2

GHSZ:

Thickness – 380 m

Volume – 2.2×109 m3



Volume of gas:

(16-32)×109 m3

0.6-1.1 tcf M

i l k o v a n d S a

s s e n , 2

0 0 3

( b a s e d o n S a g e r a n

d K e n n i c u t t ( 2 0 0 0 ) a n d p r o p r i e t a r y d a t a )


Effect of migrating brines?

Resource and economic potential



Resource and economic potential

Characteristic GC184/185

GC234/235 B

88

MC798/842

GC204

MC852/

853

AT425

Water depth (m) 500-650 500-670 650-750 807-820 850-1000 1080-

1120

1920-

1940

Resource

(m3 (×108))

(tcf)

4.9-15.9

0.017-

0.056

18.4-36.8

0.065-0.13 1.2-237

.11-0.84

.7-14

.017-0.050

251-1260

0.9-4.5114-

227

0.4-0.8

160-

320

0.6-1.1

Recovery factor High High High High High High High

Development and

production costs

Low Low Low Average Average Aver. High

Infrastructure Good Average Good Average Good Good Poor

Economic potential

(rank)Low

(6)

Low

(5)

Aver.

(3) ow

7)

Average

(2)

High

(1)

Aver

(4)

See Milkov and Sassen, 2003 (Marine and Petroleum Geology) for details

Major exploration challenges



Major exploration challenges

• Define gas hydrate plays and types of accumulations:

- No data below 6 mbsf at high flux sites;

- To date, no significant concentrations at depth <40 mbsf awayfrom high flux sites.

- Are there other gas hydrate plays? Are there shallow sandreservoirs within the GHSZ accessible to hydrocarbon charge?Are there free gas accumulations trapped by hydrates?

• Understand the variations in the GHSZ:

- What is the composition of hydrocarbon charge?

- What is the salinity of migrating fluids?

- What is the heat flow?

A new gas hydrate play?



g y p y

Gas accumulations

trapped by gas hydrates?

Image from Snyder et al. (NETL Gas Hydrate web site)

Major technological challenges



Major technological challenges

• No proven recovery technologies:

- Onshore (polar) accumulation may not be an appropriateanalogue? Depressurization is not a viable mechanism?

- Thermal stimulation with chemical inhibition? But tooshallow for horizontal wells?

• Seafloor instability. Gas hydrates appear to be relativelystable and cementing sediments at present, but theirdecomposition during recovery may result in seafloorinstability.

• Chemosynthetic communities. What are the environmentalimplications of gas hydrate recovery?

See Milkov and Sassen, 2003 (Marine and Petroleum Geology) for details

Conclusions



• The results and interpretations of gas hydrate resource potential in

the GoM bear huge uncertainties.

• Significant progress has been made during the last 5 years through

integration of available “academic” information on gas hydrate

distribution and geochemistry.

• The volume of hydrate-bound gas in the GoM may be large, but

smaller than previously thought.

• Some shallow structural accumulations in the GOM may provide

gas reserves and deserve both attention and investment. New gas

hydrate plays may emerge but need to be tested.• The academia lacks many capabilities and sometimes lacks focus.

More active involvement of industry and collaboration between

industry, academia and government are the keys to the betterevaluation of the prize.

A k l d t



Acknowledgments

Applied Gas Hydrate Research Program at GERG/TAMU

Postdoctoral Scholarship at WHOIBP America for continuous support

The scientists and crew of the R.V. Edwin Link and the Johnson Sea-Link research submersibles, University of

North Carolina at Wilmington and NOAA/NURP for

assistance in collecting deep sea floor samples.



Additional Slides

Green Canyon (GC) 234/235



y ( )

Water depth: 500-670 mArea: 612,400 m2

GHSZ:

Thickness – 400 mVolume – 0.25×109 m3



Volume of gas:

(1.8-3.7)×109 m3

0.065-0.13 tcf

Major uncertainty:

Gas hydrate distribution M i

l k o v a n d S a s s e n , 2

0 0 3 ( b a s e d o n R e i l l y

e t a l . ( 1 9 9 6 ) )

Garden Banks (GB) 388



Water depth: 650-750 m

Area: 3,200,000 m2

GHSZ:


Volume – (0.4-1.6)×109 m3


GH composition: ??-99.5% C1

Volume of gas:

(3.1-23.7)×109 m3

0.11-0.84 tcf


Gas composition?

Effect of migrating brines? M

i l k o v a n d S a s s e n ,

2 0 0 3 ( b a s e d o n R e i l l y e t a l . ( 1 9 9 6 ) )


) )



M i l k o v a n d S a s s e n ,

2 0 0 3 ( b a s e d

o n N e u r a u t e r a n d B r y a n t ( 1 9 9 0

Water depth: 807-820 mArea:

Mound – 55,600 m2

Hazy reflections – 217,400 m

2

GHSZ:


Volume – 0.16×10

9

m

3


GH composition: ?? C1

Volume of gas: (0.5-1.4)×109

m3

0.017-0.050 tcf

Major uncertainty:

Gas hydrate distribution

Documents

Fire in Ice Milkov