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7th Middle East Geosciences Conference and Exhibition
Manama, Bahrain
March 27-29, 2006
1 EOR/Harweel, Petroleum Development Oman, PO Box 81, Muscat, PC 113, Oman, phone: 968-24675448, fax: 968-24673707,
[email protected]
2 Occidental of Oman, PO Box 532, Muscat, 113, Oman
3 Exploration/Geophysics, Petroleum Development Oman, Po Box 81, Muscat, PC 113, Oman
Seismic
tuning is often considered to be an insidious effect that overprints and masks key reservoir information. However, in
the Oman Harweel Cluster of nine oil and gas fields, we are using tuning effects to better define reservoir edges and
structural geometry. In addition, our
modeling
suggests that caution must be applied to reservoir property inferences from
acoustic impedance inversions when significant
seismic
tuning is present.
Recent drilling in the Harweel Cluster yielded a challenging result when a 100m thick carbonate reservoir was completely
absent despite the appearance of simple structural continuity on the seismic
data. The post-drilling analysis showed that
noise, side-lobe effects and multiples contributed to the original illusion of continuity. However,
modeling
and
seismic
attribute analysis showed that tuning between the reservoir horizon and an overlying anhydrite unit (with intervening salt)
could very precisely delineate the termination of the reservoir.
From this work, we now understand that tuning is one of the primary controls on the reservoir's seismic
amplitude
variations. And we use these anomalies to more precisely define pinch-outs, structural truncations, and thickness variations.
Of particular value have been horizon amplitude ratios – using one horizon as a “reference” and one as a test horizon.
In addition, of interest to many inversion projects, our
seismic
modeling
shows that standard acoustic impedance inversion
may not adequately “de-tune” the
seismic
data and that amplitude artifacts may exist in the inversion volume. These
artifacts, where not properly recognized, could easily be misinterpreted as reservoir property variations.