Near surface study at the Valhall oil field from Ambient Noise Surface Wave Tomography.

A. Mordret, M. Landes, N. M. Shapiro, S. C. Singh, P. Roux and O. I. Barkved.

Wednesday 20 March 2013, by briandx // Publications

Near surface study at the Valhall oil field from Ambient Noise Surface Wave Tomography.

A. Mordret, M. Landes , N. M. Shapiro, S. C. Singh, P. Roux and O. I. Barkved

Abstract

We used 6 hours of continuous seismic noise records from 2320 4-components sensors of
the Valhall Life of Field Seismic network to compute cross-correlations of ambient seismic
noise. A beamforming analysis showed that at low frequencies (below 2 Hz) the seismic
noise sources were spatially homogeneously distributed, whereas at higher frequencies
(2-30 Hz), the dominant noise source was the oil platform at the center of the network.
Here we performed a 3D ambient noise surface-wave tomography at frequencies below 2
Hz. We used vertical-component geophones cross-correlations to extract and measure the
Scholte waves group velocities dispersion curves that were then processed with a set of
quality criteria and inverted to build group velocity maps of the Valhall area. Although
Scholte wave group velocity depends on S-wave, our group velocity maps show features
similar to that was previously obtained from P-wave velocity full-waveform inversion
of an active seismic dataset. Since the dominant noise source at high frequency (above
3 Hz) was the oil platform we determined a 2D S-wave velocity model along a profile
aligned with the platform by inverting group velocity dispersion curves of Love waves
from transverse-component geophones cross-correlations. We found that S-wave velocity
down to 20 m was low and varied along the profile, and could be used to estimate S-wave
static.

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