Detailed soil gas geochemical surveys were conducted for calibration purposes over two fields, Loma de La Lata and Filo Mirado, in the Nequen Basin, Argentina, during November of 1989 for Trend Argentina, S.A. by Exploration Technologies, Inc. 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, while Loma de La Lata is a stratigraphic trap containing an oil and gas reservoir partially underlain by a separate gas condensate reservoir.

The geochemical data consists of samples collected on 500 to 1000 meter grids placed directly over these two fields using ETI's proprietary soil gas probe technique. The free soil gases were analyzed for methane, ethane, ethylene, propane, propylene, iso-butane, and normal butane by flame ionization gas chromatography, and for helium and hydrogen by thermal conductivity gas chromatography.

The geochemical soil gas data exhibits clearly defined compositional subpopulations which match the composition of the underlying reservoirs and change in direct response to the major structural and/or stratigraphic features which control the location of the subsurface reservoirs. A single oil source is predicted at Filo Morado, in agreement with the known oilfield. Much gassier soil gas data is noted over the Loma de La Lata field where there exists an oil and gas field underlain by a gas condensate reservoir. However, a very striking change to fairly large-magnitude oil type compositional anomalies occurs directly over the northwest portion of the Lorna de La Lata field where the Quintuco oil reservoir is the only known producing horizon. A change in composition from oil to gas condensate type signatures over the Loma de La Lata field occurs across a permeability pinchout at depth which controls the updip limits of the deeper gas condensate reservoirs.

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