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