Corinne Haines Managing Director, Trimble Speaking at Seismics and the City 2015
Waveform inversion and rock physics methods for quantitative 4D seismics€¦ · ·...
Transcript of Waveform inversion and rock physics methods for quantitative 4D seismics€¦ · ·...
Waveform inversion and rock physics methods for quantitative 4D seismics
Morten Jakobsen, University of Bergen and IRIS
Outline• Acoustic waveform inversion
• for Vp
• for changes in Vp
• Elastic waveform inversion
• for elastic parameters
• for rock physics parameters
• Uncertainties in the rock physics model
Numerical experiment
• The DBIT inversion method in differential time-lapse mode will be used in an attempt to reconstruct the monitor model and the corresponding time-lapse changes, with the baseline model as the initial model.
• The grid sizes for modelling and inversion is (25m x 5m) and (100m x 5m), respectively.
• Local minima are avoided by using a multi-scale regularization technique with the following selected frequencies: (1, 3, 5, 7.5, 12, 15, 18, 20) Hz. 30
Inverted model at 40 Hz40 Hz
Velocity model inverted from noiseless seismic waveform data (DBIT)
Velocity model inverted from noisy seismic waveform data (DBIT, SN = 20 dB)
Seismic waveform inversion for rock physics parameters
Zooming in on a single grid block:
Pilskog, Lopez and Jakobsen (2014)
References• Pilskog, I., Lopez, M. and Jakobsen, M., 2015.
Linearized waveform inversion for fracture density. Extended abstract, 16th International Workshop on Seismic Anisotropy, Brazil.
• Jakobsen, M. and Pilskog, I., 2016. Gassmann-consistent Born inversion for fracture density. Extended abstract, 78th EAGE annual meeting, Vienna.
Elastic constants of the inverted model obained by ignoring the effects of pore
fluid pressure communication
Elastic constants of the inverted model obtained including the effects of pore fluid
pressure communication
Uncertainties in the rock physics model
• Are Gassmann’s formulae always valid?
• How do we model pressure effects?
• How about clay content and other parameters.
• Contact theory vs inclusion models.
Concluding remarks• The DBIT method of Jakobsen and Ursin (2015) =
a powerful tool for seismic FWI in time-lapse mode, suitable for uncertainty analysis (Eikrem et al., 2015).
• An elastic version of the DBIT method is currently under development.
• Rock physics can help FWI in anisotropic media.
• Uncertainties in the rock physics model can be dealt with in a systematic manner.