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Contents
Introduction to CGG Multi-Physics
Airborne gravity gradiometry
Adding airborne gravimetry
Examples of Applications
2
CGG Multi-physics CGG Multi-Physics focuses on non-seismic methods including gravity,
gravity gradiometry, frequency and time domain electromagnetics and magnetics
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Air • Gravity • Magnetic • EM
Land • Gravity • Magnetic • EM / MT
Sea • Gravity • Magnetic
Minerals: Base metals, Uranium, Diamonds, Precious metals, Iron, Aggregates Oil & Gas: On & offshore Government: Ground water mapping, regional mapping Environmental: Engineering studies, contaminants
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Locations o Two geographical business areas
NW Hemisphere and SE Hemisphere.
o 6 operational hubs : Toronto, Johannesburg, Rio de Janeiro, Perth, Houston, Paris
Multi-Physics Footprint
Aviation, operational, S&M hubs
Operational & sales hubs
Gravitational potential and its gradients
Gravimeters measure the gradient of the potential Gradiometers measure the gradient of gravity. Measure one, calculate the other.
U(x,y,z)
scalar field potential
Y
X
Z
U
Gxx
Y
X
Z
Gxy
Gxz Gyx
Gyy
Gyz
Gzx
Gzy
Gzz
tensor field gradient
spatial derivative
gy
gx
gz=g
Y
X
Z
vector field acceleration
spatial derivative
z
y
x
gz
U
gy
U
gx
U
=
=
=
∂∂∂∂∂∂
zzzyzx
yzyyyx
xzxyxx
GGGGGGGGG
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Airborne Gravity Gradiometry (AGG) improved data quality
IPTC-18006-MS • AGG for Rapid Mapping of Hydrocarbon Exploration Plays • David Moore
AGG acquires the lowest noise and highest resolution airborne gravity data available
6 times lower noise – 6 times better resolution
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Falcon AGG Sensitivity and Resolution
Sensitivity – RMS error in GDD at given bandwidth Resolution – half the bandwidth wavelength
– depends on aircraft speed as well as filter
Fixed-wing Falcon – 6 eotvos at 150 m
– Standard product
Fixed-wing Falcon Plus – 3 eotvos at 150 m – Only available with 2nd generation systems, more expensive
HeliFALCON – 6 eotvos at 50 m – Only available with 2nd generation systems, most expensive – Where best spatial resolution is needed or for constant height in rugged terrain
In gravity, 0.1 to 0.2 mGal RMS sensitivity
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sGrav comparison with ground truth
From Chris v. Galder & Mark Dransfield, 2016
Difference, RMS 1.5 mGal sGrav Ground gravity
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Full Spectrum Falcon – wide bandwidth, all applications!
0.3 3 30 300
0
1
2
3
4
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Shallow salt
Pressure Zones
Rifting
Bedrock
Seamounts
Mountains
Roots
Deep sedimentary basin structure
Plateaus
Underplating
Oceanic Lithosphere
Continental Lithosphere
Mantle
Ice
Oil & Gas Exploration
Mass balance
Ocean ridges
Anticlines & faults
FALCON AGG
GR
AVIT
Y ER
RO
R [m
Gal
]
WAVELENGTH [km]
Shallow statics
deep salt geometry Intra-sedimentary faults
Shallow basement
Rifts
sGrav
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Nickel exploration - West Musgraves, Australia
GDD directly detects the gabbronorite intrusion (3g/cc)
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Improvements of using helicopter over fixed wing platform
Dransfield 2007
Fixed wing
Helicopter
Fixed wing
Helicopter
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Example: North Perth Basin
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• Onshore and Offshore basin 375km NW of Perth, Western Australia.
• A FALCON survey was flown over the oilfield at 500m line spacing.
• The vertical gravity image maps out key controlling structures known from seismic surveys.
• Region of high gravity coincident with a basement horst – the main oil-trapping mechanism.
Abrolhos sub-basin Dandaragan Trough Beagle Ridge
Fault structures derived from interpretation of 2D seismic data
Example: Aptian salt over West African rifting
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High resolution gravity in regional context with full areal coverage. – Tie 2D seismic – Constrain time-to-depth conversion – Joint inversion for bottom-of-salt
Schematic geology in similar area. (Cameron & Gill, Leading Edge, 2002)
Free-air gravity. (Satellite gravity overlain by Falcon gravity.)
After Dransfield, TBP
Rifting
Salt
Recommended