Page 217 - Petroleum Geology

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rock or carrier bed. Closed contours of low potential are possible areas of
accumulation, and the contours are possible oil/water contacts.
If we take the structural contour interval to be 100 m, then u can be mapped
with 100 m contour intervals by choosing Ah so that Ahp/(p - p,) = 100 m.
Contours constructed from the intersection of the structural contours and
the contours of u are oil equipotential lines on the base of the cap rock, the
top of the carrier bed.
Fig. 9-10 is a structure map on the top of a carrier bed, and it shows a
nose plunging to the southeast. If the water is at rest, all horizontal surfaces
are equipotential and each structural contour coincides with an oil equipoten-
tial line at the intersection of an equipotential surface with the top of the
carrier bed. Oil would migrate updip and accumulate in an area of minimum
potential defined by closed equipotential contours. This would be off the
map to the north-west. The oil/water contact would be horizontal.
Figure 9-11 is a map of the potentiometric surface of the water in the carrier
bed, with a slope of indicating flow down the nose to the south-east.
Figure 9-12 is a map of u = hp /(p - p,) assuming a mass density such that
po/p = 0.8, the contour interval being equal to that of the structure map,
superimposed on the structure map.

Fig. 9-10. Structure contour map on nose plunging South-East.
Fig. 9-11. Map of potentiometric surface with slope lo-’ superimposed on the contour
map of nose (Fig. 9-10).