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Gas Hydrate Resource Assessment
U.S. Outer Continental Shelf
Independence Hub photo from Anadarko Petroleum Corp.
Matthew Frye – BOEM, Herndon, VA
Kenneth Piper – BOEM (retired), Camarillo, CA
John Schuenemeyer – SWSC, Cortez, CO
Contributors: John Grace, Gordon Kaufman, Ray Faith, William Shedd, Jesse Hunt, Pulak Ray
•Total OCS = 7.1 million km2
• ~ 15% natural gas, 27% oil
BOEM manages the exploration and development of the nation's offshore resources. It seeks to appropriately balance economic development, energy independence, and environmental protection through oil and gas leases, renewable energy development and environmental reviews and studies.
Bureau of Ocean Energy Management
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Resource Assessments: Conventional O&G v. Unconventional
Conventional Oil and Gas(existing methods)
Discovery MethodSubjective Method
Limited Spatial Resolution
Unconventional Gas Hydrate
(No Existing Methodology)
Mass Balance Method
Significant Spatial Component
What is Gas Hydrate?
What is Gas Hydrate?
Gas hydrates are ice-like crystalline substances occurring in nature where a solid water lattice accommodates gas molecules (primarily methane, the major component of natural gas) in a cage-like structure, known as a clathrate.
•Gas Hydrates are stable only in high pressure - low temperature environments
•P/T conditions are favorable on OCS where water depth > 350 meters
•Hydrate Stability Zone thickness increases as water depth increases (HSZ exceeds 1000 m thick in GOM)
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Why Are We Interested ?
Why are we interested in Gas Hydrate?
Gas hydrate dissociates into methane and water as temperature increases or pressure decreases.
• Potentially recoverable energy resource !!!
Estimated U.S. in-place gas resources – all non-hydrate
reservoirs (25,000 Tcf)
Remaining “Recoverable” (1,400 Tcf)
U.S. Methane Hydrate in-place resource
(200,000 Tcf)
Gas Resources
Produced Methane (900 Tcf)
*1995 USGS
Gas Hydrate Model Description
Model Specifications
•Stochastic - 1,000 Monte Carlo trials (capable of 4,000 trials)
•Mass Balance allows for extreme variable disaggregation / modification
•Inputs – combination of spatial and empirical data
•Outputs are GIS-ready and easily mappable
•Programmed in FORTRAN version 90 (Compiled as v. GOM3.38)•R used for summary statistics and graphics
Example Study Area – Gulf of Mexico
•Multi-channel seismic data (2D and 3D) •Wellbore data (Industry & science wells)•Modeled rates, functions, etc. 2
5°00
'
25°
00'
30°
00'
30°
00'
95°00'
95°00'
90°00'
90°00'
85°00'
85°00'
3-D coverage (~200,000 km2)2-D coverage (~225,000 km2)
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Spatial Inputs to Model
Water Depth Mobile Salt / Basement morphology
Sand Distribution Seafloor Anomalies
Example: Walker Ridge protraction area
•GOM study area ~ 450,000 km2
•202,079 model cells - each cell 2.32 km2 (5000’ x 5000’)
Model Cell Structure – Gulf of Mexico
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Gas Hydrate Model Methodology
Charge Distribution
Rock Volume Distribution
ChargeModule
Hydrate Saturation Distribution
ContainerModule
ConcentrationModule
In-Place Methane Hydrate
Distribution
IntegrationModule
Charge Distribution
Rock Volume Distribution
ChargeModuleChargeModule
Hydrate Saturation Distribution
ContainerModule
ConcentrationModule
ContainerModule
ContainerModule
ConcentrationModule
ConcentrationModule
In-Place Methane Hydrate
Distribution
IntegrationModule
IntegrationModule
In-PlaceMethane Hydrate
Distribution
Charge Module
Charge Distribution
Rock Volume Distribution
ChargeModule
Hydrate Saturation Distribution
ContainerModule
ConcentrationModule
In-Place Methane Hydrate
Distribution
IntegrationModule
Charge Distribution
Rock Volume Distribution
ChargeModuleChargeModule
Hydrate Saturation Distribution
ContainerModule
ConcentrationModule
ContainerModule
ContainerModule
ConcentrationModule
ConcentrationModule
In-Place Methane Hydrate
Distribution
IntegrationModule
IntegrationModule
Charge Module
Generation Model Migration Model
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Generation Model
Generation Productivity
Function
Asymptotic TOC Conversion Efficiency
Total Organic Carbon Mass
Base Methanogen Productivity
Sediment Temperature
Water Bottom Temperature
GeothermalGradient
Time
Thickness
GeneratedMethane
Mass
SedimentPermeability
Output
Function
Scalars
Input
FunctionArguments
Generation Productivity
Function
Asymptotic TOC Conversion Efficiency
Total Organic Carbon Mass
Base Methanogen Productivity
Sediment Temperature
Water Bottom Temperature
GeothermalGradient
Time
Thickness
GeneratedMethane
Mass
SedimentPermeability
Output
Function
Scalars
Input
FunctionArguments
Pro
babi
lity
Den
sity
Weight percent TOC
0.0 0.5 1.0 1.5 2.0
0.0
0.5
1.0
1.5
Pro
babi
lity
Den
sity
Weight percent TOC
0.0 0.5 1.0 1.5 2.0
0.0
0.5
1.0
1.5
Generation Model Output
Charge: Generation model Output
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Migration Model
Charge: Migration model two end members100% vertical and 100% dip-driven
At 100% vertical, all gas generated in a model cell remains in that cellGeneration per cell = gas charge per cell
Top of Salt spatial input
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GIS Analysis
Top Salt structure map
Flow Direction
Basin
GISHydrologic
Tools
Top Salt structure withHydrodynamic catchments
Curvature GIS tool
Curvature map w/ catchments
White = negative curvatureBrown = positive curvature
Dip-Driven Gas Migration
100% dip-driven migration continued…….
At 100% dip migration, all gas within a catchment basin is redistributed to cells with + curvature
Curvature Map 100% Dip Migration Map
Sum Generation, by Catchment
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100% dip-driven migration continued…….
At 100% dip migration, all gas within a catchment basin is redistributed to cells with + curvature
Dip-Driven Gas Migration
Migration Model
Which migration method is correct?
100% Dip Driven
Gas migrates to margin of basins
100% Vertical
Gas remains in cell of origin
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Migration model
Based on sensitivity analysis using known seafloor seeps…….
Mixing Ratio 60:40 dip v. vertical
Mean Charge
Container module
Charge Distribution
Rock Volume Distribution
ChargeModule
Hydrate Saturation Distribution
ContainerModule
ConcentrationModule
In-Place Methane Hydrate
Distribution
IntegrationModule
Charge Distribution
Rock Volume Distribution
ChargeModuleChargeModule
Hydrate Saturation Distribution
ContainerModule
ConcentrationModule
ContainerModule
ContainerModule
ConcentrationModule
ConcentrationModule
In-Place Methane Hydrate
Distribution
IntegrationModule
IntegrationModule
Container Module
Gross HSZ ‐ UZ = Net HSZ
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where, B = water depth in meters C = thickness of the hydrate stability zone in meters
geothermal gradient water bottom phase stabilitytemperature expression
f(B) = -(-9.6 x ln(B) + 88.4) x C/1000 – 295.1 x B-0.6 + 8.9 x ln(C + B) – 50.1
Stability Equation (from Milkov and Sassen, 2001)
sediment temperature expression
Container Module
GrossHSZ
Salt
Undersaturated Zone (UZ)
Net HSZ
High Charge = Thin UZ Low Charge = Thick UZ
thickness inversely related to Charge:
Container Module
UZ
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Net HSZ (= Gross HSZ – UZ)
Container Module
Charge Distribution
Rock Volume Distribution
ChargeModule
Hydrate Saturation Distribution
ContainerModule
ConcentrationModule
In-Place Methane Hydrate
Distribution
IntegrationModule
Charge Distribution
Rock Volume Distribution
ChargeModuleChargeModule
Hydrate Saturation Distribution
ContainerModule
ConcentrationModule
ContainerModule
ContainerModule
ConcentrationModule
ConcentrationModule
In-Place Methane Hydrate
Distribution
IntegrationModule
IntegrationModule
Concentration Module
HSZ porosity, by lithologic facies
Pore space saturated by gas hydrate
Concentration Module
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Concentration Module
5000’
zT
Shale Void = (Volume)(Porosity)Volume Shale = (x)(y)[(T)(1-sand%)]Porosity Shale = f(d)
Sand Void = (Volume)(Porosity)Volume Sand = (x)(y)[(T)(sand%)]Porosity Sand = f(d)
From Container Module:(T) Net HSZ thickness(d) Midpoint depth net HSZ
From input file:sand %
Sand %
x
Concentration Module
Mean = .095
Concentration
*decimal % of the bulk rock volume
*
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Integration Module
Integration Module
For each model cell, we:
•Compare charge to available container retain smaller of two
•Except at surficial anomalies manually fill if undercharged
•Convert from RTP to STP: P
roba
bilit
y D
ensi
ty
Conversion Factor
140 145 150 155 160 165 170
0.0
0.5
1.0
1.5
2.0
2.5
Beta(5,1.6) mean=164,mode=168
Pro
babi
lity
Den
sity
Conversion Factor
140 145 150 155 160 165 170
0.0
0.5
1.0
1.5
2.0
2.5
Beta(5,1.6) mean=164,mode=168
Charge Distribution
Rock Volume Distribution
ChargeModule
Hydrate Saturation Distribution
ContainerModule
ConcentrationModule
In-Place Methane Hydrate
Distribution
IntegrationModule
Charge Distribution
Rock Volume Distribution
ChargeModuleChargeModule
Hydrate Saturation Distribution
ContainerModule
ConcentrationModule
ContainerModule
ContainerModule
ConcentrationModule
ConcentrationModule
In-Place Methane Hydrate
Distribution
IntegrationModule
IntegrationModule
Assessment Results - Graphical
0
20
40
60
80
100
50 150
250
350
450
550
650
750
850
950
1050
1150
1250
1350
Mor
e
In-Place gas Hydrate (TCM)
Fre
qu
ency
0%
20%
40%
60%
80%
100%
Cu
mu
lati
ve P
rob
abil
ity
Frequency Cumulative %100%
80%
60%
40%
20%
0%0
20
40
60
80
100
50 150
250
350
450
550
650
750
850
950
1050
1150
1250
1350
Mor
e
In-Place gas Hydrate (TCM)
Fre
qu
ency
0%
20%
40%
60%
80%
100%
Cu
mu
lati
ve P
rob
abil
ity
Frequency Cumulative %100%
80%
60%
40%
20%
0%
Mean Total = 607 TCM (21,444 TCF)
U.S. GOM In-Place Results (1,000 trials)
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Assessment Results - Spatial
New Orleans
o In Place resource estimate – not necessarily technically/economically recoverable
o No introduction of geologic risk – petroleum system success on all trials
Summary
Conclusions - GOM:
•Resource assessment methodology different than typical O&G assessmentsSpatial rather than strictly empirical
•Advanced GIS tools used to model gas generation and migrationFlow Direction, Basin, Curvature
•Approach applicable to other O&G basins around the world with proper modifications to account for local subsurface geometries and data availability
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Pacific OCS
Pacific Outer Continental Shelf
• Complex tectonics (subduction, spreading, wrench)• Several point source sediment systems• Near-shore basins• Relatively thin sediment cover in places• Paucity of seismic data
Model Changes
• 100% vertical gas migration• Crust age & BSR incorporated• Mixed spatial/empirical inputs• HSZ constrained by sediment thickness
*Official results release expected 3Q 2012
Pacific OCS – Spatial Inputs
2D Seismic Data DSDP/ODP wells
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Pacific OCS – Spatial Inputs
Water Depth Sediment Thickness
Crust Age
Pacific OCS – Spatial Inputs
Bottom Simulating Reflectors (BSR)
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Pacific OCS – (partial) Spatial Inputs
Sand DistributionTotal Organic Carbon
Pacific OCS - Outputs
Gas ChargeHydrate Stability Zone (HSZ)