Interpretation and analysis of sandstone bodies of the Castillo and Bajo Barreal Formations (Cretaceous) in the Cañadon Vasco Oil Field, Golfo San Jorge Basin, Santa Cruz, Argentina

GRIGNOLA, S.; GEORGIEFF, S.M.; FERREIRA, L.

Mendoza

Congreso; 18th International Sedimentological Congress; 2010

International Association of Sedimentologists

The Cañadón Vasco oil field is located in the southern border of the Golfo San Jorge Basin (Argentina); near to the oil field, the Ballena Hill shows extensive fluvial deposits belonging to Bajo Barreal Formation. Thus, a stratigraphic correlation between them was proposed by using seismic data. The Ballena Hill and the Cañadón Vasco oil field show a strong tectonic control by a NW-SE normal fault reversed during Late Cretaceous. The resistivity imaging logs allowed identifying sedimentary structures, thicknesses, contact hierarchies, measure paleocurrent directions and other details (e.g. biotubation, intraclasts, root fragments and grain size). These data were compared with cutting samples and outcrops data in order to improve the sedimentological model for Bajo Barreal and Castillo Formations (Cretaceous). The integration of cutting samples (grain size and color) and resistivity image logs allowed obtaining a stratigraphic log. Twelve sandstone bodies belonging to Bajo Barreal and Castillo Formations were analyzed following this method and ten litho-facies were defined from this study. The litho-facies assemblages were assigned to channel, crevasse channel, channel bar, splay and floodplain deposits. The sandstone bodies thickness, trough cross stratification and paleocurrent directions were used specific equations to obtain the channel belt width. The sandstone bodies were also associated with the SP and resistivity wire-logs to define a group of electro-facies. Finally, seismic horizon slices related with the sandstone bodies studied were also analyzed as intent to merge litho– and electro-facies assemblages and seismic geoforms. As paleocurrent directions coming from image logs as seismic horizon slices are coincident in to point out several changes in the channel pattern and sinuosity. Most noticeable change occurs for those strata belonging to the lower section of Bajo Barreal Formation (informally named “tobácea section”). The sinuosity increases from 1.15 to around 2 and the channel belt wide reaches 500 m. The sedimentary model of electro-facies may apply to wells (in the same or another oil field) without assistance of image logs but with available 3D seismic information.