Scattering effect on shallow gas-obscured zone imaging in Bohai PL19-3 area

X Zhu, K Wallace, Q Zhu, R Hofer - Geophysics, 2012 - pubs.geoscienceworld.org
X Zhu, K Wallace, Q Zhu, R Hofer
Geophysics, 2012pubs.geoscienceworld.org
Seismic imaging is challenging in the Bohai Bay PL19-3 area, offshore China. Bohai Bay
Field is seismically obscured, making well penetrations the only reliable source of data for
subsurface interpretation. With the help of turning-ray tomography, we are able to obtain a
reliable near-surface velocity model approximately down to 700 m below sea level, using
the first arrivals picked from streamer data. Depth migration using velocities estimated from
turning-ray tomography has improved shallow structures and fault definition. However …
Abstract
Seismic imaging is challenging in the Bohai Bay PL19-3 area, offshore China. Bohai Bay Field is seismically obscured, making well penetrations the only reliable source of data for subsurface interpretation. With the help of turning-ray tomography, we are able to obtain a reliable near-surface velocity model approximately down to 700 m below sea level, using the first arrivals picked from streamer data. Depth migration using velocities estimated from turning-ray tomography has improved shallow structures and fault definition. However, reservoir level structures from 800 to 1500 m are still poorly imaged. A viscoelastic modeling study with assigned variable Q and shallow velocity profiles, with and without shallow gas-induced scatterers, demonstrates that scattering is the primary controlling phenomenon causing imaging difficulty within the obscured zone. Due to scattering, imaging tests at the target level were unsuccessful even with precise knowledge of velocity.
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