Soil Gas Calibration Surveys over the Filo Morado and Loma de La Lata Oil and Gas Fields in the Neuquen Basin, Argentina

JONES, VICTOR T., Exploration Technologies, Inc., Houston, TX

Detailed soil gas geochemical surveys were conducted for calibration purposes over two fields: Loma de La Lata and Filo Morado in the Neuquen basin in Argentina during November, 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 separate gas-consensate reservoir.

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

The geochemical soil gas data exhibit clearly defined compositional subpopulations that match the composition of the underlying reservoirs and change in direct response to the major structural and/or stratigraphic features that control the location of the suburface reservoirs. A single oil source is predicted at Filo Morado, in agreement with the known oil field. 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 Loma de La Lata field where the Quintuco oil reservoir is the only known producing horizon. A change in composition from oil to gas condensa e type signatures over the Loma de La Lata field occurs across a permeability pinch-out at depth that controls the updip limits of the deeper gas condensate reservoirs.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)