AGU 2015 Fall Meeting Session ID: 8656 Session 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 Majdański Institute of Geophysics, Polish Academy of Sciences Loučeň Castle,

People involved in grant DEC-2012/05/B/ST10/00052 PI: Majdański Main investigators: Malinowski, Środa Investigators: 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 experiment Standard 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 domain Joint interpretation Borehole data verification Section in depth domain PSDM

Industrial reflection data examples Shot gathers CDP gathers SHOT 10091SHOT CDP 706CDP 2424

Seismic imaging Processing:  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 domain NWSE

Wide-angle data Surprisingly strong observations at first interpreted as a high velocity refractions. Latter identified as a wide- angle postcritical reflections

WARR interpretation > 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] Depth [m*10] Mean velocity profiles Depth [m*10] Vt/Vs Velocity ratio

PSDM result Porownac migracje: Migracje glebokosciowa po skladaniu RRRmigra.stack – stack RRR903v2 FDMIG z predkosciami RRR0903v4.nmo I migracje glebokosciowa przed skladaniem (MM_depth_migra.stack) Wyczyscic stack (poststack fk, semblance, itp.) Z migracja anizotropowa ??? Wczytac segy do matlaba (grd z Vz zrobiony na segy w /dssm/data/tmp), oraz model jive (wyniki.txt) i zapisac przegridowany model jiva do segy żeby się dalo wczytac do GC, tam się zrobi grd i będzie można poscic migracje – cos zle zadzialalo, bo się ilosc cdp nie zgodzila i nie ma naglowkow w segy :/

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