A Sedimentary Quantitative Model for the Bajo Barreal Formation (Cretaceous): Integration between Outcrops and Subsurface Data. San Jorge Basin, Santa Cruz, Argentina

FERREIRA L., GEORGIEFF S.M., SANTANGELO A. , KAMERBEEK Y.

San Miguel de Tucumán

Conferencia; 9th International Conference on Fluvial Sedimentology; 2009

Universidad Nacional de Tucumán - IESGLO

The outcrops around the La Sin Nombre Lake belong to the Bajo Barreal Formation (Cretaceous, Chubut Group). These deposits are analogs to the hydrocarbon-bearing reservoirs in the adjacent Cerro Guadal Norte oil field (YPF SA). At the present day, the Bajo Barreal Formation is the major oil unit in the San Jorge Basin (Santa Cruz Province, Argentina). The distance between outcrops and the nearest oil well is about 600m and this one is towards the East-Northeast direction of the outcrops. In the outcrops, the dip ranges from 45ºE (in the base) to 15ºE (at the top). A vertical stratigraphic profile was measured in the outcrops and 15 fluvial sandstone bodies were recorded. The thicknesses of the sandstone bodies vary from 1.5 to 3 m and the width from tens to hundreds meters. The paleocurrent measurements indicate that the outcrops are normal to oblique to the paleoflow direction and the sinuosities were obtained. In the other hand, a detailed analysis was performed in the oil-well by using microresistive log images, cuttings and a set of log-curves. The log images allowed defining the synthetic sandstone-bodies; besides, the sedimentary structures, the thickness, and estimations of paleocurrent directions were recorded. By comparing the surface deposits with the images, it was possible to make a facies analysis and define the presence of fluvial bars and channels. Thus, the stratigraphic correlation between outcrops and the oil well mentioned above is performed by using the seismic sections. A set of seismic horizons were developed, which is considering the amplitude as a seismic attribute and useful tool to define fluvial geoforms (Santangelo et al., 2009). The integration among data (outcrops, oil-well and 3D seismic) allowed obtaining important fluvial parameters. The width is from 150 to 250 m, while the sinuosity varies from 1.15 to 1.35. The Bridge and Tye’s (2000) equation was applied to calculate the channel-width from log images, although these values were 25% higher to those measured in outcrops and seismic horizons. The data coming from different sources (surface and subsurface) enable to optimize the quantitative sedimentary model for the Bajo Barreal Formation and improve the oil and gas reservoir characterizations.