3203307
Description
Flashcards by misstasvir, updated more than 1 year ago
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Created by misstasvir
over 8 years ago
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| Question | Answer |
| COHERENCE ATTRIBUTE | WHAT IS COHERENCE ATTRIBUTE? |
| - Measurement of similarity among the seismic traces/wavelets - calculate localised waveform similarities in both in-line and cross-line | Highly coherent: indicate laterally continuous lithologies Low coherent: indicate changes in waveform (fault/fractures) |
| Why use coherence? | a) Traditional seismic TSL are used for interpreting fault that are perpendicular to the strike b) Becomes complicated when fault runs parallel to strike - lineaments look alike c) Stratigraphy features are unidentifiable with small scale |
| Methods of measuring coherence | a) represent the trace - to - trace similarity and produce interpretable changes b) similar traces are mapped with high coherence coefficients and discontinuities have low coherence c) works based on spatial window of neighbouring traces |
| Cross - correlation based coherence - sensitive to waveform - operates in 3 neighbouring traces (2 targets, 1 master) - value = 1 = high coherence | |
| Semblance based coherence i) Define space and a time aperture ii) Define dip and azimuth for each point iii) Calculate ratio of energy of all the traces along a specified dip iv) Measure degree of similarities to each other of all the traces along the selected dip within the selected square or elliptical outline v) might include noise and low frequency unwanted data | |
| Variance based coherence > most popular > almost identical to semblance method > Variance = 1 - semblance estimate coherence > measure of how well each trace fits the mean trace > if all traces are identical/similar = 0 > if all traces are identical but of different amplitude = > 0 | Variance = 1 - |
| Coherence enhances : * Faults and fracture system *Channels *Edge detection *Other geological features | > easy visualisation of geological feature > sharp detection of reef, channel boundaries and deltaic sediments > unbiased view of the features in seismic volume > no interpretation required > extract meaningful details, improve accuracy & time effectiveness |
| THANK YOU | TASVIR KAUR , 17987 |
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