Join Seismic Image Processing from 27th to 29th November at PETEX Olympia London Booth D8.

1. Kirchhoff eGWMKirchhoff eGWM
Polarity Reversal at Base
Small issue with near angles on steep
dips, which is being fixed in R&D
Correct AVO (No Leakage in the grabens and
structure below is better amplitude image Polarity Reversal at Base
FALSE AVO (Leakage in the grabens and
below is poorly imaged
0 - 15º inTime
RTM 50Hz Image eGWM 50Hz Image
15 - 30º inTime 30 - 40º inTime 0 - 15º inTime 15 - 30º inTime 30 - 40º inTime
eGWM: multipath, one-way wave equation
• Steep dip source term, VTI, TTI & Q
Kirchhoff: single path, high-frequency approximation
• Velocity models must be smooth
RTM: multipath, multimode, two-way wave
• Velocity model must be precise
Migration Algorithm
• Naturally images broadband data
• Attenuates multiples and surface waves
• Computation in the slowness domain
• Self-adjoint operator
• Space and slowness (angle) available during migration
• Increased accuracy and stability
eGWM Advantages
Kirchhoff vs eGWM - Zoom 3Kirchhoff vs eGWM - Shallow Zoom 1
PSDM Stack - Overlay VelocitiesSIP eGWM (50Hz) vs RTM (50Hz) - Colour Display
Kirchhoff Angle Gathers StackeGWM Angle Gathers Stack
Input:
• Industry standard RTM used to run 50Hz
• Input - processed shot gathers
• Input maximum offset - 10km
• Aperture used - 20km full aperture
Observations:
• Generates noise at the interface of large velocity
contrast top/base salt
• Require more time to complete one iteration of
RTM
• Doesn’t honour true amplitudes
• Expensive to output gathers and not practical
Input:
• SIP eGWM used to run 50Hz
• Input - processed shot gathers
• Input maximum offset - 10km
• Aperture used - 20km full aperture
Observations:
• Noise free compared to RTM, due to implementation of
absorbing boundary conditions
• 15 times faster to output eGWM stack image
• Very cheap to output gathers
• Honours true amplitudes
• Output offset and angle gathers simultaneously
Pwave Swave Density
eGWM vs Kirchhoff Offset Gathers in DepthAngle Gathers 0-30° in Time - eGWM vs Kirchhoff
Fluid Factor in Depth - eGWM vs KirchhoffAngle Gathers 0-30° in Time - eGWM vs Kirchhoff
Shots and CMPS from Synthetic WavefieldElastic Wavefields to Generate Synthetic Shots
Fluid Response
AVO Response
Class-3 atTop
Class-2P at Base
Noise from near
angles ~0-3˚
Top: Class-3
Base: Class-2P
Fluid Response
RTM eGWMThis example is a 2D broadband acquisition from the
Inner Moray Firth area of the UKNS acquired for the
OGA in 2015.The comparison is an RTM vs eGWM
both migrated usingVTI assumption.
Unmigrated SHOTS
eGWM Kirchhoff
eGWM Kirchhoff
eGWM Angle Gathers 0-30°
eGWM Kirchhoff
Kirchhoff Angle Gathers 0-30°
Unmigrated CMPS
CDP Location
CDP Location