Page 171 - Petroleum Geology

TABLE 7-5

The world’s ten largest oil fields in 1968 ranked according to ultimate recoverable reserve
estimates (from Halbouty et al., 1970, table I, facing p. 504). Figures in thousands of
millions of barrels
__
Reserves Zipf constant

1 Ghawar 75 75
2 Burgan 66 122
3 Bolivar 30 90
4 Safaniya-Khafji 25 100
5 Prudhoe Bay 20 100
6 Samotlor 15 90
7 Kirkuk 15 105
8 Romashkino 14.3 114
9 Rumaila 13.6 122
10 Abqaiq 12.0 120
100 Quirequire 1 .o 100

150 Santa Fe 0.615 92
____ __.__

TABLE 7-6
The sizes of the ten largest oil accumulations in the world predicted by Zipf’s law if the
total ultimate recoverable reserves are 1800 X lo9 bbl. Figures in thousands of millionsof
barrels
-
1 2 3 4 5 6 7 8 9 10
150 75 50 38 30 25 21 19 17 15

If the ultimate recoverable reserves are 1450 thousand million barrels,
Rank 300 would contain 400 million barrels of recoverable oil and Rank
100,000 would contain 1.2 million. If there are 1800 thousand million barrels,
Rank 300 would contain 500 million, and rank 100,000 would contain 1.5
million. We have already found more than 300 fields with more than 400
million barrels - indeed, nearly 300 with more than 500 million - so even
the larger figure may be conservative. This figure of 1800 X lo9 bbl is compa-
rable with the 2000 X lo9 bbl estimated by Moody and Esser (1975) by other
means. The largest 15 accumulations would contain 28% (3.32/12) of the
total, and the 264 largest accumulations would contain 51% (6.16/12). The
1975 figures (Moody and Esser, 1975, p. 17, table IV) are 35 and 72%, re-
spectively, suggesting that if Zipf’s law is valid for oil accumulations, there
has been a successful bias towards the larger accumulations. The ten largest
accumulations predicted by Zipf’s law for total ultimate recoverable reserves
of 1800 X lo9 bbl are shown in Table 7-6. This is a plausible result, and