Modelling and Characterization of a Fluvial Low Net-to-Gross Reservoir: The Case Study of a Mature Oil Field for EOR in the Bajo Barreal Formation, Golfo San Jorge Basin, Argentina

Abstract

The Golfo San Jorge Basin in Argentina represents an intraplate basin related to the Mesozoic aperture of the Atlantic Ocean. The Upper Cretaceous Bajo Barreal Formation (BB Fm), objective of this study, consists of ∼600 to 1500 meters-thick continental fluvial succession, interbedded with variable proportion of volcanic material. This reservoir, producing hydrocarbons since 1920s, still appears to be underexploited, due to variable degree of success of primary and water-flooding campaigns possibly explained by poorly connected reservoir sandstones and presence of heavy oil. Traditionally, sand bodies were interpreted and correlated as isolated reservoirs, with limited lateral extension and low vertical heterogeneity. Some recent studies have been developed to better understand reservoir connectivity and heterogeneity in order to improve oil primary and secondary recovery. This include seismic analysis, spectral and multivariate attribute analysis for facies distribution, geochemical logs for chronostratigraphic correlations, and the use of conceptual models honoring outcrops and core descriptions. This work aims at developing a robust understanding of the depositional system, needed as input to 3D geological models for EOR. Our modelling strategy is based on sector models that capture the highest reservoir heterogeneity, in order to follow realistic hydrocarbon and polymer paths in the subsurface. A characterization of the distribution, geometry, and properties of sandstone reservoirs is proposed, leading to new depositional 3D models for the BB Fm. Based on detailed cores, logs, and seismic geometries analysis, the BB Fm can be interpreted as deposited in an extended fluvial fan system. Depositional cycles are here determined by the vertical stacking of genetically related units, mostly defined by a sharp erosive base and fining and thinning upwards trends. Such high frequency reservoir architecture suggests the predominance of autocyclic processes combined with the presence of lower frequency allocyclic factors such as intense volcanic eruptions. We consider these paroxistic events as playing one of the roles in triggering sediment availability and supply to the fluvial-dominated reservoir system. Integration of information from different sources with a conceptual model, detailed numerical 3D models was built that could describe quite well rock properties spatial distribution. This led to reliable predictions for decision support in EOR projects.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016