GRT Imaging for Seismic AVO/AVA Inversion

GRT Imaging for Seismic AVO/AVA Inversion
significantly reducing amplitude uncertainty and
obtaining more accurate elastic attributes
Seismic Image processing Ltd is offering our velocity model building and GRT solutions to many clients across Norway and UK. All our PSDM projects have been through GRT imaging.
Any questions and clarifications please send an email to admin@seismicimageprocessing.com; Jagat.deo@seismicimageprocessing.com;
Please visit our website: http://www.seismicimageprocessing.com/

As the down-turn in the oil and gas industry started 2 years ago, SIP took a
brave and strong decision to invest in R&D to implement the next generation
of imaging algorithms to address the major seismic data challenges, reducing
risk and uncertainty for our clients, and obtaining the highest quality seismic
products for hydrocarbon exploration and production. SIP have focused on
the following 3 major developments:
1. Ray based imaging algorithms- single arrival vs multi arrival (Kirchhoff vs
GRT)
2. Wave based imaging algorithms- Extended full guided wave imaging
(RTM/WEM/Beam vs eGWM-much faster than current industry imaging
algorithms- results to be published soon)
3. Velocity Model Building – eFWI using AutoImager velocity model as
starting model (Tomography vs eFWI- includes refraction and reflection
energy)
This article explains the raytracing methods and the advantages of multi
arrival imaging for AVO/AVA exploitation.
Introduction

Standard imaging workflows and algorithms using Kirchhoff have led to the
following:
A multitude of examples of the industry drilling dry holes on AVO prospects.
It could be due to genuine rock physics ambiguity or misconceptions on the
gathers output from Kirchhoff Time or Depth migration:
Anisotropy, Tuning, denoise, RMO, TRIM Statics, Offset balancing
Modelling gathers to look for match with seismic
There is considerable effort to make gathers appear clean & flat using data
conditioning tools instead of asking more fundamental questions on the
accuracy of the velocity model and imaging. Our expectations from any
migration code is:
Denoise using absorbing boundary conditions.
Accurate Velocity & Eta -- so no requirement for subsequent RMO.
Spherical divergence corrections -- so no requirement to match modelled gathers with offset scaling.
Ability to accurately handle and image multi-arrival travel times.
We compare the current standard Kirchhoff code to a more advanced multi
arrival imaging algorithm. We refer to this as GRT- Generalized Radon
Transform- angle domain depth Imaging.
Issues

Kirchhoff will image only one arrival, whereas GRT is a multi-arrival code
hence preserves the amplitudes and the structural definition with much more
clarity and detail. As shown in the figure below.
GRT Concept

Why the seismic industry needs a multi arrival imaging code?
It is apparent that many of companies in the industry are putting a lot of effort in getting the right
seismic data by adopting the latest and greatest acquisition techniques coming on to the market.
For example – dense cables / dense receivers / dense nodes / dense shooting patterns / sim
sources or blended acquisitions / etc. Most (more than 40%) of the acquired data is redundant
and discarded during the regularization stage of the seismic processing, and also when the
remaining data is passed through Kirchhoff PSDM. This is where the imaging code will only image
single arrivals thus generates a lot of noise and most importantly loses the information from the
arrivals of different ray paths, which may contain the true amplitudes of the reflected events of
the subsurface.
GRT Concept

So far SIP (Seismic Image processing Ltd) have completed numerous production jobs to validate
the GRT PSDM against the industry Kirchhoff PSDM imaging code. GRT produces more reliable
true amplitude information where the AVA theory holds true. Project after project we have
experienced significantly higher quality images to map new exploration targets, including proof of
dry holes that had been originally drilled using Kirchhoff PSDM images, which had falsified the
amplitudes (see the examples below)
The Solution and Examples

NOTE: the ringing event on the Kirchhoff
image (below left)looks like a residual
multiple which is not present on the image
with multi-arrival code (GRT). Also the faults
are clearly sharper with less noise and less
smearing across the fault boundary
The Solution and Examples

AVA- Elastic attributes example
Conclusions: So far all the GRT projects have delivered superior results compared to Kirchhoff. It
is time for the industry to move on to a new generation of imaging codes and workflows to
reduce the risk and uncertainty of understanding the amplitudes of the true reflectivity of the
subsurface.
Conclusions

GRT Imaging for Seismic AVO/AVA Inversion

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