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Fig. 11-2. Map of La Brea-Pariiias, Peru, showing relationship between structural eleva-
tion in feet (solid lines) and sand/shale ratio (dashed lines). (After Youngquist, 1958, pp.
700-701, figs. 4 and 5.)

so of overburden on the productive Oficina Formation.
These are strong arguments for the source-accumulation relationships of
eastern Venezuelan crude oil, and are worth studying because similar arguments
are applicable to other areas.
Youngquist (1958) concluded that migration had been short in the La Brea-
Pariiias field, Peru, and that the faults, which moved contemporaneously (or
nearly so) with sediment accumulation, acted as seals. The oil and gas are
found in Eocene sandstone reservoirs at depths between 1000 and 2000 m,
but there is no discernable reason for the occurrence of oil, gas, or water, in
a particular sand because there is no discernable pattern to their distribution.
Nor does structural relief have its usual influence because, in general, the
sands in the highest structural positions are wet.
Most remarkable of his findings (and one well worth investigating in other
areas) is that the sand/shale ratio has a controlling influence (Fig. 11-2 and
11-3). Sandfshale ratios greater than 1.2 in LaBrea-Pariiias are not conducive
to the generation and pooling of petroleum, and he concluded that sedimen-