Combined Geochemical Methods for the Surface Exploration of the Neuquén Basin, Argentina*

The following discusses exploratory research of surface geochemistry in an area located 30 km west of Senillosa town, Neuquen Province, Argentine (Figure 1). The petroleum system is composed by Jurassic source rocks and Jurassic-Cretaceous clastic and carbonatic reservoirs. The exploration survey comprised a number of transects with equidistant sampling stations where soil samples were taken for microbial (buthanotrophic bacteria) and trace elements analysis. In addition, vegetation indexes (Shannon Diversity (H) and Species Richness (S)) were obtained at each sample station (Figure 2). Several transects and maps were obtained to identify potential biomarkers of micro-leakages. The results obtained from bacterial analysis show high background values (those less than 2,500 cfu/g), while those corresponding to the blocks (structures north middle and south) were in the range of 2,500 to 17,500 cfu/g (Figure 3). The fault-associated anomalies cover up to 180,000 cfu/g (Figure 4). Abnormally high background values could be due to the activity of deep petroleum systems that emit signals from both source rocks (Vaca Muerta and Molles Formations) and associated reservoirs (Larriestra et al., 2010a, b). Soil trace elements like vanadium, nickel, chromium and copper were found related to elevated blocks and faults and they were associated with the oil generated in the Vaca Muerta Formation source rock, whose main feature is the presence of vanadium, nickel