A modern analog for meandering rivers of the Mina del Carmen Formation (Albian) at Cañadón Seco oilfield, Golfo San Jorge Basin, Patagonia

Abstract

Fluvial sandstone reservoirs within the Mina del Carmen Formation (Albian) currently produce up to 10% of the liquid hydrocarbons of the Golfo San Jorge Basin, mainly from isolated channel belts encased in a fine-grained, pyroclastic-rich floodplain. In spite of their economic importance, no modern analogs for the subsurface fluvial reservoirs have been proposed yet, mainly due to the reduced thickness of the channels in relation to the vertical resolution of available 3-D seismic surveys. At Cañadón Seco oilfield (South Flank of the Golfo San Jorge Basin), the planform of a meandering channel belt in Upper Mina del Carmen Formation has been imaged in a 3-D seismic dataset using seismic attributes. The meandering channel belt is up to 13 m thick and 3200 m width, with a sinuosity of 3.61 and has an average channel width of 192 m. Using the measured parameters obtained from the seismic dataset, we tested the applicability of empirical relations developed for modern rivers; the results of the statistical equations showed a close correspondence with seismic measurements and allowed us to estimate data of formative river discharge and upstream catchment area for the subsurface example. Both values were then parallel with a database of river discharge and area of up to 1018 hydrometeorological stations in drainage catchments around the world. Nine rivers of the database show discharge-area values comparable to those obtained using empirical equations. After a review of satellite imagery of the nine areas, a modern analog for the subsurface example was found in the Middle Ebro River (Spain). The analog consists of a meandering fluvial depositional system in a foreland basin setting, with seasonal discharge variability. The approach followed in the research can be of use to any fluvial basin, but considering that fluvial systems are highly variable in scale, geometry, pattern and composition, the extrapolation of results to other regions or even to other strata within the Mina del Carmen Formation, should be done with caution.