Oil and Gas Imaging Bruce VerWest, PhD Research Manager – External & Strategic R&D CGGVeritas Pumps & Pipes 1 November 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 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

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 Forward problem Inverse problem Non-unique Incomplete Unstable Acquisition Seismic data Model building Imaging

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

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 Time (sec) Receiver station Source

Multiplicity of data helps in noise removal

Traveltimes from data at varying offsets yields information about medium velocity

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

Kirchhoff Beam 1-way Wave Equation Jack Discovery – Different 3D Imaging Algorithms

Changing the acquisition geometry to improve imaging Narrow Azimuth Acquisition Wide Azimuth Acquisition N S N S Jack #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 Totals Cpu’s >15060 Memory >32 TBytes Disk > 3676 TBytes

Supercomputer Peak Performance 1980 1990 2000 2010 Year Introduced 1 Pflop Peak Speed (flops) 1 Tflop 1 Gflop 1 Mflop CRAY-1 CRAY-2 X-MP4 Y-MP8 SX-4 SX-5 T3D T3E Doubling time = 1.5 yr. Blue Gene (367 Tflops) CGGVeritas Houston

Recent Advances to Improve Imaging More accurate (and expensive) imaging algorithms Better tools for velocity model determination Increased acquisition aperture

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

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 1 November 12, 2007