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4_TIKIM_basics

By Jonathan Ferguson,2014-05-27 15:04
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4_TIKIM_basics

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     TIKIM The Basics

     Part 3: Contents TIKIM Basics:

     What it does! Basic Tenets

     Use of Header words

     Main features

     Migration aperture Acquisition irregularity handling

     Basic run time issues

     February 2009

     TIKIM - The Basics

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     TIKIM : What it does! BASIC TIKIM performs Kirchhoff Time Migration

     On pre-stack 2D or 3D data.

     Outputs can be Migrated traces corresponding to different offsets as gathers (e.g. CMPs) Migrated traces corresponding to different velocity perturbations (can be stacked to provide velocity scans) Stack of all the individual migrated traces generated by the algorithm.

     For use in structural velocity analysis or AVO studies.

     Migrated stacked volume

     February 2009

     TIKIM - The Basics

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     1

     TIKIM in Context: PreSTM sequences

     TIKIM

     One Pass Kirchhoff migration using 3D VRMS velocity field

     At first sight the fact that TIKIM is a ??one-pass?? solution indicates ??onea simpler job flow. However th abilities of TIKIM to act as a velocity analysis tool, H the biliti f t t l it l i t l and to handle anisotropy mean that the job flows can be complex - with several (typically 3) runs of TIKIM being applied.

     February 2009

     TIKIM - The Basics

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     TIKIM : What it does! 3 STEPS or ALL in 1

     How TIKIM works??

     There are three main steps??..

     1. Input of seismic data, with associated auxiliary data 2. Distribution of data to the processing CPUs and

     migration computation

     3. 3 Output of the migrated data

     TIKIM can run all of these steps in one job, for job, instance in 2D or, especially where large 3D surveys are concerned, in separate jobs

     February 2009

     TIKIM - The Basics

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     TIKIM : What it does! FAST TURNAROUND

     For fast turnaround TIKIM can be run simultaneously on numerous processors ? Either on ??clusters?? or traditional multi-CPU machines.

     Th output d The data are split into ??Chunks??. li i ??Ch k

     February 2009

     TIKIM - The Basics

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     2

     TIKIM: Basic Tenets

     Some basic principles of TIKIM parameterisation are fundamentally different to that normally used in Geocluster.

     The definition of the data to be processed by TIKIM is referenced to the OUTPUT, not the INPUT. 3D TIKIM DOES NOT use the input data header words associated with the processing grid (4 and 19). i t d ith th i id d 19) If the parameter DCDP is coded, TIKIM performs a 2D migration. The trace position is defined according to the content of word 4. TIKIM DOES refer to Word 6 (mutes) This is used as a start time for migration

     February 2009

     TIKIM - The Basics

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     TIKIM: Pre-TIKIM QC

     WARNING

     When reprocessing data obtained from other contractors be aware that the provided ??topographic references?? may be different to CGG convention.

     At the start of the pre-processing stage??.

     It is strongly recommended (or mandatory!) to re-compute the relevant trace header words from Source/receiver co-ordinates.

     February 2009

     TIKIM - The Basics

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     TIKIM Main Features

     Let us now review most of the major features of TIKIM??.

     Input requirements Hyperbolic move-out assumptions and ??migration aperture?? moveFull pre-stack time migration preAcquisition irregularities compensation

     February 2009

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     TIKIM : Inputs

     Processing inputs are pre-NMO traces pre(corrected for spherical divergence).

     Their input sort order is of no importance to TIKIM.

     It is therefore usually determined by the requirements of the p prepre-TIKIM processing flow p g

     February 2009

     TIKIM - The Basics

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     Hyperbolic Moveout : Migration Aperture

     TIKIM a Kirchhoff Diffraction Summation Method migration ??. works by summing along locally defined hyperbola.

     ?C if the velocitis above the diffractor are not isotropic the diffraction will not be truly hyperbolic

     We assume a limited

     approximation to a hyperbola ??.

     ??..defined by the migration aperture

     February 2009

     TIKIM - The Basics

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     Hyperbolic Moveout : Migration Aperture

     The migration aperture is chosen in conjunction with the velocity large enough to encompass the dip but small enough to be unperturbed by lateral velocity variations

     Slow velocities = narrower aperture

     Fast velocities = wider aperture

     the migration aperture

     the migration aperture

     Lateral variations to Vrms are permitted and result in variations to the hyperbola from place to place??.however, there are constraints and laterally smooth velocity fields are preferred

     February 2009 TIKIM - The Basics 12

     4

     Acquisition Irregularity Compensation

     TIKIM input offsets 150m150m-250m

     Difference when only using 50 % of the input traces

     Difference after random noise removal

     Conclusion: TIKIM is robust in that certain acquisition irregularities can be compensated for without significant loss of quality.

     February 2009 TIKIM - The Basics 13

     TIKIM : Outputs

     TIKIM can output migrated gathers or stacks. TIKIM can be used as a migration velocity scanning tool??

     Percentage Velocity Scanning giving the so called Perturbed velocity scans (structural velocity analysis)

     The output sort order can be the same as the input, or different from the input

     February 2009

     TIKIM - The Basics

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     TIKIM velocity scans

     97%

     100%

     103% Initial velocity TIKIM velocity scan using perturbed initial model velocity model Final velocity model for production run Velocity picking on the resulting velocity scans

     February 2009 TIKIM - The Basics 15

     5

     Full Kirchhoff PSTM ?C TIKIM

     106% 103% 96% 93% 100%

     February 2009

     TIKIM - The Basics

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     TIKIM : Cluster/Parallel Implementation

     TIKIM has been designed to efficiently use large ??PC clusters to allow processing of the many millions of output traces created during the migration of large 3D surveys.

     TIKIM can also be run on ??conventional?? multi-CPU machines or, for very small surveys (probably 2D lines) on single CPU machines.

     February 2009 TIKIM - The Basics 17

     TIKIM status: Run Time Issues Run time issues

     Total run time may be conveniently regarded as due to two components?? ? Actual CPU computation time ? May be influenced by user by choice of parameters (e.g. aperture size) ? I/O (Overhead trace transfer) time

     May be influenced by user by choice of data handling method (e.g. use of TIKIM IN) For the programmers these are interrelated: A program change to decrease computation time may cause an increase in I/O time!

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     Summary

     TIKIM

     No sorting actually needed

     ?C although sorting may be advisable for best machine use / and crash

    job recovery / restarts

     Coherent NMO & migration velocity field

     Handles reasonable velocity variations

     Target oriented

     Flexible algorithm ? elevations, converted waves, anisotropy

     February 2009

     TIKIM - The Basics

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