Page 215 - Geochemical Remote Sensing of The Sub-Surface

192 V. 7". Jones, M.D. Matthews and D.M. Richers
TABLE 5-XVI

Success rates of surface gas geochemistry in petroleum prospecting in Azerbaijan (Zorkin et al.,
1982)

Province Positive prognosis Negative prognosis
Areas Correct % Areas Correct %
Apsheronskaya 8 7 87 - - -
N izh n i ek uri n skaya 4 3 75 - - -
Kirovobadskaya 10 7 70 8 7 87
Kobystano-Shemahinskaya 4 2 50 6 6 100
Total 26 19 70 14 13 90

however, the risk that information about spatial variability within a cell is lost and so is
the information about the absolute magnitude of individual samples.
On the basis of anomalous magnitudes, Zorkin et al. (1982) showed that, in 90% of
cases, the soil-gas technique correctly identified areas lacking hydrocarbon potential in
Azerbaijan, and correctly identified areas with hydrocarbon potential in 70% of cases
(Table 5-XVI). Although the distinction of ambient from secondary background is often
relatively straightforward, the distinction becomes ambiguous in areas with effective
seals, such as stable intracratonic salt basins.

CASE HISTORIES

Numerous case histories illustrating the relationship of surface seeps to their
associated production are given in the cited references. Four surveys, three onshore and
one offshore, are selected here to demonstrate and confirm the compositional
relationships defined above. The first onshore example consists of calibration grids
conducted over two fields in the Neuquen Basin of Argentina, and the second example is
a sniffer survey conducted for calibration purposes over gas-productive areas in the High
Island area of the Gulf of Mexico. The two other onshore surveys are located in the
Great Basin of Nevada and in the Overthrust Belt of Wyoming-Utah.

Neuquen Basin, Argentina

Detailed soil gas geochemical surveys were conducted for calibration purposes over
two fields, Filo Morado and Loma de La Lata, in the Neuquen Basin in Argentina. These
two fields were chosen for this calibration study because of their differences in both
reservoir composition and entrapment mechanisms.
Filo Morado is an anticlinal oil field producing from the Agrio Formation at a depth
of 3000 m (10,000 feet). Loma de La Lata consists of two stratigraphically-trapped