Neuquen Basin

Sedimentological heterogeneities in fluvial reservoirs constitute significant flow barriers, which can be described on a variety of scales. The main elements to consider for an integrated evaluation of multi-scale heterogeneities in fluvial successions are disparities in stratigraphic distribution, the nature of bounding surfaces, spatial changes in facies associations and lithofacies. Moreover, porosity and permeability distributions based on a multi-scale reservoir characterization shows a better representation of the effective permeability architecture. However, the impact of multi-scale heterogeneities on reservoir properties are usually underestimated during modelling workflows, and may eventually affect the recovery of hydrocarbons. To address these issues, this study reports the sedimentological heterogeneities recognized in the Mulichinco Formation fluvial succession, which is exposed in the Sierra de la Vaca Muerta Anticline and Cerro Mesa, in the southern-margin of the Neuquén Basin, Argentina. Although these fluvial deposits are included in the main tight-gas reservoirs of the basin, variations between large- to small-scale sedimentary elements and their potential role as a flow barrier have not yet been analyzed in an integrated way. 

The studied interval includes five main sedimentary units, which defines a population of 148 channel-units represented by 64 (43,2%) gravelly-sand braided channel bodies, 51 (34,5%) sandy braided channel bodies, 28 (19%) meandering channel bodies and 5 (3,4%) terminal channel bodies. They are all interbedded between floodplain deposits. The channel-units were described using a width/thickness ratio, the scale of bounding erosive surfaces (small- to large scale), vertical storey development, dominant in-channel accretion style (the presence of downstream or laterally accrediting bars), dominant lithofacies and petrophysical properties (porosity, permeability, and density). Four potential scales of sedimentological heterogeneities have been identified: lamina, lithofacies, facies association and the stratigraphic distribution of channel-units. This work shows that a multi-scale characterization approach could be implemented to estimate changes in property distribution in a braided to meandering fluvial reservoir type. 

Leading scientist: Dr. Mariana Olivo. Project in cooperation with Dr. Diego Kietzmann (University of Buenos Aires, Argentina).