AGU 2015 Fall Meeting

Session ID: 8656Session Title: New development in open source and academic seismic software

Conveniors: Majdański, Polkowski

Velocity in the sedimentary layers from post-critical reflections

dr hab. Mariusz MajdańskiInstitute of Geophysics, Polish Academy of Sciences

Loučeň Castle, 12.06.2015

People involved in grant DEC-2012/05/B/ST10/00052

PI: MajdańskiMain investigators: Malinowski, ŚrodaInvestigators: Czuba, Gaczyński, Białas, Trzeciak

Field team: Okoń, Dec, Grzyb

Thanks to

1. Amplitudes of seismic observations in layered models

2. Postcritical reflections idea and synthetic test

3. Braniewo piggyback experiment

4. Field data application (seismic imaging & tomography)

5. Conclusions

6. Extra – joint interpretation

Plan

Amplitudes of observations

Majdański et al., 2006, Tectonophysics

Amplitudes of observations

Unusual observations in the sediments(Koło 2013 experiment, profile 15)

Amplitudes of observations

Typical crustal

structure

High velocity

contrasts

Sedimentary structure

Postcritical reflections in sediments

Velocity in the second layer:

from refraction

from postcritical

reflections

The shape of boundary:

From near-vertical

reflections

Synthetic data

Equally spaced 11 shots 99 receivers

Synthetic results

Refraction

Refraction & short offset reflection

Refraction & post-critical reflection

Braniewo experimentStandard prospecting profile (PGNiG

S.A.)

20 km long

516 shots (477 vibroseis, 39 TNT)

50m shot spacing

480 active channels

12.5 m receiver spacing

Piggyback experiment (IGF PAS)

60 stations (vertical 1C 4.5Hz)

300 m spacing

Full spread acquisition (max. 20 km)

Full-spread recordings

Data interpretation scheme

Wide-angle data

Industrial reflection data

Imaging

Travel time tomography

Section in time domain

Layered velocity model

Structure model in

depth domainJoint interpretation

Borehole data

verification

Section in depth domain

PSDM

Industrial reflection data examples

Shot gathers

CDP gathers

SHOT 10091 SHOT 10774

CDP 706 CDP 2424

Seismic imagingProcessing:

Geometry from sps Spectral equalization of vibroseis nad

dynamite shots Static corrections Ground roll attenuation by fk filtering Noise attenuation by fx deconvolution cdp sorting Velocity analysis Bandpass filtering Predictive deconvolution Nmo correction Random noise attenuation by fk

filtering Stack Post-stack fk filtering Semblance smoothing

Result in time domainNW SE

Wide-angle data

Surprisingly strong observationsat first interpreted as a high velocity refractions.

Latter identified as a wide-angle postcritical reflections

WARR interpretation

> 25 000 picks

3000 cdp

Inversion of traveltimes

Conclusions

Traveltime inversion in sediments is different comparint to the crustal scale – we need to change our habits

Full-spread recording of refraction – cheap and easy to perform

Combination of refraction and reflection data – easy way to significantly improve our recognition of velocity distribution

Work in progress …

How we can make use of those velocities?

Simple post-stack transformation to depth domaim using Vrms

Velocity fields – depth domain

Difference in velocities

Velocity [m/s]

Dep

th [m

*10]

Mean velocity profiles

Dep

th [m

*10]

Vt/Vs

Velocity ratio

PSDM result

Anisotropic (VTI) PSDM result

Initial results of VTI type anisotropic PSDM

PreStack Depth Migrations

Initial tests – effect of the low velocity layer

To do …

Correct PSDM using anizotropic velocities (vertical from Vrms & boreholes, horizontal from tomography)

Test the effect of low velocity layer of PSDM

Estimation of the uncertainty of the seismic interpretation

This work has been financed by the Ministry of the Higher Education in form of a NCN grant DEC-2012/B/ST10/00052

I would like to thank the PGNiG S.A. for providing us with the reflection data from the Braniewo experiment, and a great help with performing refraction measurements

Thanks to the organizers for the great workshop in the Loučeň Castle

Acknowledgement