Caracterização de unidades de fluxo multi-escala em reservatórios fluviais: o exemplo do campo de Alto Rodrigues - Bacia Potiguar, Brasil

Abstract

Petrobras' divestment plan for mature fields created a new scenario for oil exploration and production in Brazil's onshore and shallow water sedimentary basins. Several small and medium-sized companies are acquiring these fields with the challenge of implementing projects that increase production and the recovery factor of these accumulations. Mature fields typically have more than 30 years of production and have dozens or even hundreds of producing wells, with an immense amount of rock, fluid, and associated production data. Therefore, data integration studies to generate knowledge about the producing reservoirs are mandatory, so that new production development projects can be implemented, aiming to maximize the return on capital invested in the revitalization of these fields. This study integrates geological/geophysical, petrographic/diagenetic, and petrophysical data to individualize rocks with different flow capacities producing oil in a field in the Potiguar Basin, NE, Brazil. The work used information from more than 800 vertical wells, 19 of which have rock data and petrophysical analysis. Seven wells provided most of the data for the present study because of the greater thickness of cores recovered. Implementing the multiscale approach that we presented was essential in understanding the geological aspects that influence the reservoir production capacity. At the micro scale, for example, through the study of thin sections, it was possible to identify and recognize clay minerals that occur may obstruct pore throats and, consequently, affect the permeability and productivity of the rocks. At the meso scale, the study of cores in different portions of the field allowed us to characterize the depositional systems in the area and identify factors that influence the entry of oil into the reservoir. Finally, through the correlation of rock vs. logs at the macro scale, we estimated the distribution of the flow units defined for the other wells, thus allowing the construction of maps and petrofacies sections with geological and dynamic significance. At this last scale, we visualize the geometry of the sedimentary deposits and their heterogeneities, whose understanding directly influences the planning and development of an accumulation (for example, in the definition of the production wells grid and water or steam injection in case of application of secondary recovery methods). Additionally, a methodology was developed to quantify the production capacity of the rocks from a reservoir quality index (RQI) that we validated with field production data.