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Oil and Gas Imaging
Bruce VerWest, PhDResearch Manager – External & Strategic R&DCGGVeritas
Pumps & Pipes 1November 12, 2007
Goal of Seismic Imaging
Seismic Imaging – a primary tool for oil & gas exploration Determine reservoir geometry, shape, position Determine reservoir properties – lithology, pore fill
(brine, oil or gas)
Approach and challanges
Seismic Acquisition – Listening for Echos
Marine Acquisition
Plan view
Seismic Acquisition – Listening for Echos
The Tool Acoustic echos (5-80 Hz.) Image reflected energy Subsurface velocity unknown Velocity complex -> ray path distortion
Limitations of data acquisition Data acquired on one side of target – the earth’s surface Reservoir details are on order of meters – seismic
wavelengths are tens to hundreds of meters We are interested in subsurface properties but we
measure property contrasts
Seismic Imaging
Acquisition
Seismic data
Model building
Imaging
Forward problem Inverse problem
Non-unique
Incomplete
Unstable
Non-unique
Incomplete
Unstable
Seismic Imaging is a Two Step Process
Determine velocity -> Acquire data with varying source receiver separation Use stereo tomography to determine velocity Traveltimes yield low resolution view of subsurface
velocity
Image data -> Back propagate measured sound wavefield to form
image Various approximations to the acoustic wave equation
are utilized
Iterative process since the velocity is part of the image
Multiple source receiver separation data
Multiplicity of data helps in noise removal
Traveltimes from data at varying offsets yields information about medium velocity
Receiver station
Tim
e (
se
c)
Receiver stationSource
An Example - Subsurface Model
An Example – Complex Wave Propagation
An Example – Seismic Data
x
t
An Example – Imaging Velocity
x
z
An Example – Imaged Output
x
z
KirchhoffKirchhoff BeamBeam 1-way Wave 1-way Wave EquationEquation
Jack Discovery – Different 3D Imaging AlgorithmsJack Discovery – Different 3D Imaging Algorithms
Changing the acquisition geometry to improve imaging
Narrow Azimuth Acquisition Wide Azimuth Acquisition
NS NSJack #1 Jack #1
x
X X
Repeat Over 1000’s of sq. km.
Detailed depth top salt interpretation covering 19,000 sq km
CGGVeritas Town Park Computer Center
Computer TotalsCpu’s >15060
Memory >32 TBytesDisk > 3676 TBytes
Supercomputer Peak Performance
1980 1990 2000 2010
Year Introduced
1 Pflop
Pe
ak
Sp
ee
d (
flo
ps
)
1 Tflop
1 Gflop
1 Mflop
CRAY-1CRAY-2
X-MP4 Y-MP8
SX-4
SX-5
T3D
T3EDoubling time = 1.5 yr.
CGGVeritas Houston
Blue Gene(367 Tflops)
Recent Advances to Improve Imaging
More accurate (and expensive) imaging algorithms
Better tools for velocity model determination
Increased acquisition aperture
Current Problems in Seismic Imaging
Poor illumination – shadows, absorption
Complex velocity model determination (including anisotropy)
Imaging steep dips and complex structure
Resolution –> loss of high frequencies and higher velocity at depth
Multiple reflections
Other Noise
Oil and Gas Imaging
Pumps & Pipes 1November 12, 2007
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