Geophysical data acquisition - OGS

from different data vintages, is unique. At the reservoir, the P and S velocities
should not be constrained at all, because their variations (and the resulting ratio)
is the primary information that we are looking for. Thus, we will have a set of
coupled models, one of each vintage year, that are mostly identical, except in the
upper layer and at the reservoir. When a proper amplitude-preserving surfaceconsistent
processing is carried out, including a vintage cross-calibration, we can
carry out a pre-stack depth migration of each vintage, and compare the reflectivity
changes at the reservoir. AVO can add further details, and guide the design of the
tomographic grid.
Sound speed in the seawater estimated by the joint inversion of
reflected and head waves in the year 1989 (above) and 1992 (below)
in the same area at the North Sea.
Seismic tomography for environmental studies
G. ROSSI
F. ACCAINO
G. BÖHM
G. DAL MORO
G. MADRUSSANI
M. PERONIO
A. VESNAVER
The oil and gas industry pushed seismic technology at advanced levels by
significant investments, which rarely are available for environmental studies.
However, except for a scale factor, many practical problems encountered in
hydrology within the shallowest Earth layers are very similar to those ones
considered in the hydrocarbon reservoirs. Seismic tomography is a possible
example: the inversion of velocity anomalies can be generally related to lateral
facies variations of the geological formations and, sometimes, to variation of other
properties of hydraulic interest – as permeability and porosity. If both P and S
waves can be jointly inverted, various analytic expressions exists which related
these velocity fields to the fluids’ pressure and saturation.
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