This paper presents the application of reservoir geochemistry for the study of an unconventional reservoir, the Vaca Muerta Formation, in three oil fields located in Neuquén Basin, Argentina.
The main objective of this study consisted in the characterization of production oils from different levels of the Vaca Muerta Formation. 99 oils corresponding to different production levels, Cocina, Upper Organic and Lower Organic, were analyzed: to establish differential geochemical characteristics of each landing zone. Additionally, the monitoring of molecular composition changes over time was performed.
The oils from Cocina, Lower Organic and Upper Organic levels were geochemical identified in the three studied fields. The n- and iso-paraffins, isoprenoids and Iso-Heptane value, among others, allowed to differentiate the productive levels vertically and regionally, in accordance with the maturity conditions. Oil's compositional variation/evolution over 12 months of production was tested, where the first samples showed the lowest °API density and the highest C20+.
The results allowed, in each field, to evaluate the geochemical characterization of oils in each level and to differentiate between them. Due to these results, it was also possible to analyze the composition of the produced oil over time as well as to perform production allocation that would allow inferring possible interference between Landing Zones at the startup of the wells. These approaches combined with other techniques would improve the understanding of the Vaca Muerta Formation at different scales (well, pad and reservoir), providing information to optimize the vertical and horizontal spacing of wells.
The use of geochemistry to solve production problems has been demonstrated in Argentinian reservoirs, as shown for Neuquén Basin by the work of Labayén et al. (2004 and 2005), Milicich et al. (2016) and Fasola et al (2005) in the Golfo de San Jorge Basin. All these studies have focused on the characterization and allocation of oil production in conventional reservoirs.
