Gravimetry and gravity gradiometry technologies at CGG Multi-Physics

Tianyou Chen*, Mark Dransfield

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

3

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

4

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

5

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

6

Einstein

Galileo

Feynman

6 FALCON AGG Systems are in Operation

Cavendish

Newton Newton

7

Kepler

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

8

FALCON Plus

Gravity Wavelength and Amplitude

9

sGrav – strapdown airborne gravimeter

sGrav

10

sGrav comparison with ground truth

From Chris v. Galder & Mark Dransfield, 2016

Difference, RMS 1.5 mGal sGrav Ground gravity

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sGrav repeatability

From Chris v. Galder & Mark Dransfield,2016 12

Full Spectrum Falcon – wide bandwidth, all applications!

0.3 3 30 300

0

1

2

3

4

5

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

13

Nickel exploration - West Musgraves, Australia

GDD directly detects the gabbronorite intrusion (3g/cc)

14

Improvements of using helicopter over fixed wing platform

Dransfield 2007

Fixed wing

Helicopter

Fixed wing

Helicopter

15

Example: North Perth Basin

16

• 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

17

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

Thank you