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 

The geochemical data come from 239 shallow probe (1.2 metre, 4 feet) soil-gas samples collected on 500 - 1000 m grids placed directly over these two fields, with 95 sites over Filo Morado and 144 sites over Loma de La Lata. The free soil gases were analysed for methane, ethane, ethylene, propane, propylene, iso-butane and normal butane by gas chromatography using a flame ionisation detector. 

The compositional subdivisions are derived from the published literature (Nikonov, 1971 Jones and Drozd, 1983) and are the same as those shown in Table 5-VIIl. The shade of each of the anomaly clusters suggests the oil versus gas potential of the anomaly according to these empirical divisions alone. 

Ratios of methane/ethane, methane/propane and methane/total butanes for all sites that exceed the median of the data are also shown in Figs. 5-31 and 5-32, in order to provide a visual illustration of the composition of the anomalous data. The bimodal nature of the Loma de La Lata soil-gas data is clearly shown by the red (gas) and green (oil) populations whilst Filo Morado stands in stark contrast, with its unimodal oily (green) population and lack of gas-type anomalies. 

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