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6 DEPOSITIONAL SYSTEMS
Fig. 6.45. An example of a complex petroleum reservoir in coastal sands. Isopach map of the Aux Vases Formation (Upper Mississipian) sands in the Rural Hill field, Illinois, USA. Well locations are not shown, but the
field has been drilled up with a well-spacing of some 300 m, so the contours are tightly constrained. Shoreline
sands trending NE-SW along the paleostrike are cross-cut at right angles by channel sands aligned along the
paleodip. (After Weimer et al., 1982, American Association of Petroleum Geologists Bulletin, AAPG 9 1982,
reprinted by permission of the American Association of Petroleum Geologists whose permission is required
for further use.)
for a sand may be proved. Reference has already been m a d e to instances of p e t r o l e u m
t r a p p e d in "shoe-string" barrier island sands in the Cretaceous basins of the Rocky
Mountains of C a n a d a and the USA.
Figure 6.45 illustrates the problems of producing p e t r o l e u m from a reservoir composed of paleostrike trending barrier bar sands into which are cut paleodip aligned channel sands. These two types of reservoir are interbedded with impermeable nonreservoir
shales.