Interpreting Time-lapse Information

Time-lapse analysis and interpretation

Reservoir changes observed in 4D seismic images (see figure to right). The 1999 (bottom) survey clearly shows the effect of production when compared with the baseline survey of 1985 (top). The change in the seismic reflection strength of the top of the reservoir is related not only to the saturation change, but also to the original oil-column height. When water replaces oil, the acoustic impedance in the reservoir increases, causing a dimming effect on what used to be a strong response from the top of the reservoir. The strong seismic response from the oil-water contact (OWC) in 1985 has also been dimmed due to production. Red and yellow represent a decrease in acoustic impedance, while blue colors represent an increase. Structure, lithology, and fluid content are shown in the cross-sectional models on the right.

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