Surface Geochemical Studies over Stratigraphic Traps: Examples from the Neuquen Basin, Argentina

Daniel C. Malizia¹, Luis Álvarez², Graciela Prestia¹, and Luigi Clavareau^3
1 Geo-Microbial Technologies Sudamerica, Buenos Aires, Argentina
² Repsol-YPF Argentina
³ Geo-Microbial Technologies, Paris, France

A high percentage of the new prospects and developing oil fields in the Neuquen basin possess a strong stratigraphic component in their trapping mechanism. Detailed surface geochemical surveys of such fields and prospects have proven to be highly effective, since they can delineate the hydrocarbon distribution within reservoirs that in many cases are difficult to predict or image with other methods. Surface geochemical surveys can be applied (1) to high grade the plays or exploration prospects on the basis of their hydrocarbon charge as determined by the presence of positive surface geochemical anomalies, (2) in development projects by identifying bypassed pay, reservoir heterogeneities, and reservoir compartment boundaries, and (3) to monitor reservoir drainage over time through use of repeat geochemical surveys. These applications are especially useful in field with multiple reservoirs, reservoir compartments, and bypass zones that are not being effectively drained.

In the Neuquen basin, where probably 50% of the traps are represent stratigraphic traps or combined structural-stratigraphic traps, this technology has been successfully used to identify new exploration leads and prospects as well as to high-grade seismically-defined prospects on the basis of probable hydrocarbon charge. Additionally, surface geochemical methods are effective in imaging hydrocarbon microseepage from traps in those parts of the basin overlain by basalts, areas in which seismic data are of poor quality due to the unfavorable geology and surface conditions. These various applications will be illustrated with examples from the Neuquen Basin.