Difference between revisions of "Procesamiento sísmico"

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==Habilidades técnicas en geofísica==
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=Convetional Seismic data processing=
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Le contrôle qualité des données sismiques (cartes, positionnement, couverture, statiques, offset)
 
  
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Building earth velocity models for a variety of geophysical applications, including depth conversion of interpretation data, 2D and 3D isotropic and anisotropic pre-stack depth migration.
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==Yilmaz (2001)==
  
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Créer des rapports de QC
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{| class="wikitable"
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! align="center" | '''"1'''
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Connaissance des principaux formats de données sismiques et de positionnement (SEGY, SEGD, UKOOA, normes OGP, etc.)
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! align="center" | ''''''
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! align="center" | ''''''
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Reviews and inspects QCs in archiving processes.
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|-
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| Pre-processing" || Démultiplexage || "Demultiplexing
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Send to the client test jobs for validation, prepares weekly reports
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| Orders seismic data by seismic trace instead of being ordered by time. Multiplexed recording is still found in older data or in current data shots with old recording instruments." ||  ||
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|-
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==Otras==
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|  || Reformatage || "Reformatting (SEG-Y/SEG-D)
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|-
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Generate and present results both through written reports and oral presentations.
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| Puts the data in a format that is understandable by computers (e.g. SEG-Y format, SEG-D format, etc.)." ||  ||
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|-
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|  || Édition || "Seismic data edition
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|-
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| Searchin for noisy, monofrequency and incorrect polarities traces. ||  ||
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|-
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| examines seismic data for bad, noisy, and\or monofrequency traces, and deletes them, and also spots any traces with incorrect polarities and corrects them." ||  ||
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|-
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|  || Correction de la dispersion géométrique || "Geometrical spreading correction
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|-
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| It is also called amplitude correction. Because the signal becomes weaker as it moves away from its source (i.e. its amplitude decreases with time), amplitude correction is needed to count for this lose, and to make amplitudes stronger." ||  ||
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|-
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|  || Géométrie de terrain || "Set-up of field geometry – Geometry QC
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|-
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| Incorporates field geometry with seismic data processing. Coordinates, shot\ receiver locations and spacing must be entered to the system carefully and precisely because processes like CMP sorting, for example, highly depend on this. ||  ||
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|-
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| http://radexpro.com/scope/qc/" ||  ||
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|-
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|  || Corrections statiques || "Application of field statics corrections
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|-
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| This is needed for land data collected on non-flat areas. It reduces the travel times into a common datum level. The datum could be the sea level or any other local datum." ||  ||
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|-
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| 2 || Déconvolution et normalisation des traces || "Deconvolution and trace balancing
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|-
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| Deconvolution makes the signal look better by increasing the temporal resolution and removing echoes. Trace balancing makes the amplitude uniform." ||  ||
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|-
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| 3 || Triage par CMP || "CMP sorting
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|-
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| Sorts the data into CMP gathers, so it can be corrected for the NMO and stacked after that (see step 7)." ||  ||
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|-
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| 4 || Analyse de vitesse || "Velocity analysis
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|-
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| Gives info about velocities in the subsurface layers. It finds the stacking velocity (very close in value to the RMS velocity) that best fits our data (This step may be delayed after step 5)." ||  ||
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|-
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| 5 || Corrections statiques résiduelles || "Residual statics corrections
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|-
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| Counts for near-surface velocity variations that causes some static and dynamic distortion problems." ||  ||
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|-
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| 6 || Analyse de vitesse || "Velocity analysis
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|-
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| (see step 4). If we have residual statics problems, we do velocity analysis after we count for them." ||  ||
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|-
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| 7 || Correction NMO || "NMO Correction
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|-
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| Counts for the increase in travel time with increasing offset distance. This increase makes flat reflectors look dipping, and makes dipping reflectors look even more dipping. The amount of correction needed decreases with depth, so that shallower reflectors get more “stretched” than do the deeper ones. ||  ||
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|-
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| Muting: It is just a fancy word for deleting a part of a trace. Muting a whole trace is called “killing”." ||  ||
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|-
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|  || Correction DMO ||
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|-
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|  || Correction NMO inverse ||
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|-
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|  || Analyse de vitesse ||
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|-
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|  || Correction NMO ||
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|-
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| 8 || Sommation || "Stacking
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|-
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| After sorting the data into CMP gathers and applying the NMO correction, reflectors line up nicely and hence their stacking gives a stronger signal. Multiples\ random noises do not line up. Stacking increases S/N ratio by decreasing multiples\ random noise from the data which enhances the overall quality. It also reduces the seismic data volume to the plane of the seismic section" ||  ||
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|-
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| 9 || Déconvolution ||
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|-
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| 10 || Blanchiment de spectre à temps variable ||
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|-
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| 11 || Filtre à temps variable || "Time- variant band-pass filtering
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|-
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| Filters unwanted “signals” based on their frequencies. For example, ground roll has a lower frequency (and higher amplitude) compared to the rest of the section, so we can filter it out based on that fact." ||  ||
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|-
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| 12 || Migration || "Migration
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|-
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| So far, each trace is plotted under its CMP location which puts reflectors in the wrong subsurface location. Migration process moves those reflectors into their true subsurface locations, and that improves lateral resolution. Migration also collapses diffractions into identifiable points on the seismic section." ||  ||
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|-
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| 13 || Gain || "Gain recovery
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|-
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| Seismic energy gets lost in many different ways (e.g. scattering, frication, etc.). Gain is the inverse function of energy loss. It is very hard to predict the attenuation function because primary reflections, multiple reflections, and random noise have different decay functions. Instead, we examine (test) different gain values, and see which value gives a better looking data. " ||  ||
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|}

Revision as of 22:48, 21 February 2016

Convetional Seismic data processing


Yilmaz (2001)

"1 ' '
Pre-processing" Démultiplexage "Demultiplexing
Orders seismic data by seismic trace instead of being ordered by time. Multiplexed recording is still found in older data or in current data shots with old recording instruments."
Reformatage "Reformatting (SEG-Y/SEG-D)
Puts the data in a format that is understandable by computers (e.g. SEG-Y format, SEG-D format, etc.)."
Édition "Seismic data edition
Searchin for noisy, monofrequency and incorrect polarities traces.
examines seismic data for bad, noisy, and\or monofrequency traces, and deletes them, and also spots any traces with incorrect polarities and corrects them."
Correction de la dispersion géométrique "Geometrical spreading correction
It is also called amplitude correction. Because the signal becomes weaker as it moves away from its source (i.e. its amplitude decreases with time), amplitude correction is needed to count for this lose, and to make amplitudes stronger."
Géométrie de terrain "Set-up of field geometry – Geometry QC
Incorporates field geometry with seismic data processing. Coordinates, shot\ receiver locations and spacing must be entered to the system carefully and precisely because processes like CMP sorting, for example, highly depend on this.
http://radexpro.com/scope/qc/"
Corrections statiques "Application of field statics corrections
This is needed for land data collected on non-flat areas. It reduces the travel times into a common datum level. The datum could be the sea level or any other local datum."
2 Déconvolution et normalisation des traces "Deconvolution and trace balancing
Deconvolution makes the signal look better by increasing the temporal resolution and removing echoes. Trace balancing makes the amplitude uniform."
3 Triage par CMP "CMP sorting
Sorts the data into CMP gathers, so it can be corrected for the NMO and stacked after that (see step 7)."
4 Analyse de vitesse "Velocity analysis
Gives info about velocities in the subsurface layers. It finds the stacking velocity (very close in value to the RMS velocity) that best fits our data (This step may be delayed after step 5)."
5 Corrections statiques résiduelles "Residual statics corrections
Counts for near-surface velocity variations that causes some static and dynamic distortion problems."
6 Analyse de vitesse "Velocity analysis
(see step 4). If we have residual statics problems, we do velocity analysis after we count for them."
7 Correction NMO "NMO Correction
Counts for the increase in travel time with increasing offset distance. This increase makes flat reflectors look dipping, and makes dipping reflectors look even more dipping. The amount of correction needed decreases with depth, so that shallower reflectors get more “stretched” than do the deeper ones.
Muting: It is just a fancy word for deleting a part of a trace. Muting a whole trace is called “killing”."
Correction DMO
Correction NMO inverse
Analyse de vitesse
Correction NMO
8 Sommation "Stacking
After sorting the data into CMP gathers and applying the NMO correction, reflectors line up nicely and hence their stacking gives a stronger signal. Multiples\ random noises do not line up. Stacking increases S/N ratio by decreasing multiples\ random noise from the data which enhances the overall quality. It also reduces the seismic data volume to the plane of the seismic section"
9 Déconvolution
10 Blanchiment de spectre à temps variable
11 Filtre à temps variable "Time- variant band-pass filtering
Filters unwanted “signals” based on their frequencies. For example, ground roll has a lower frequency (and higher amplitude) compared to the rest of the section, so we can filter it out based on that fact."
12 Migration "Migration
So far, each trace is plotted under its CMP location which puts reflectors in the wrong subsurface location. Migration process moves those reflectors into their true subsurface locations, and that improves lateral resolution. Migration also collapses diffractions into identifiable points on the seismic section."
13 Gain "Gain recovery
Seismic energy gets lost in many different ways (e.g. scattering, frication, etc.). Gain is the inverse function of energy loss. It is very hard to predict the attenuation function because primary reflections, multiple reflections, and random noise have different decay functions. Instead, we examine (test) different gain values, and see which value gives a better looking data. "
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