Inversion - 3-D Seismic Interpretation - page 165

Fig. 6.6 Section from an inverted 3-D dataset.

planning development, for example in choosing locations for producers and water-
injection wells.
Another example is shown in fig. 6.8 . In this case the reservoir is the Upper Jurassic
Magnus sand of the UK Northern North Sea. The figure shows the location of a cal-
ibration well and the picked top and base of the reservoir sequence. In this case the
reservoir unit contains interbedded sands and shales. The upper part of the figure shows
an inverted section from the 3-D volume. The sands are hard relative to the shales,
and the application of an impedance cutoff allows separation of sands from shales; in
the lower part of the figure this has been applied to separate sands (shown in grey)
from shales (in pink). The next step would be to estimate porosity in the sands; in this
particular study a stochastic approach was used, and the results will be shown after
explaining the underlying principles in the next section.
Inversion is also a useful tool for the study of carbonate reservoirs. For example,
Story et al . ( 2000 ) were able to use an inverted dataset to map zones of high and
low porosity within a producing reef. Because of its shallow depth (3800 ft), high
seismic frequencies could be recorded, and a resolution of 14 ft was achieved in the
inverted dataset. Mapping of low-porosity, low-permeability tight zones was critical to
an understanding of reservoir behaviour during production; the tight zones turned out