Analysis of the Efficiency of Petroleum Systems in Fluvial Environments in the Rift Context of the South and North Atlantic: Brazil and Portugal

Abstract

The present article exhibits the achieved results based on the evaluation of two petroleum systems, which compares reservoirs of fluvial environments of sedimentary basins located in the south and north Atlantic, in Brazil (Recôncavo Basin) and in Portugal (Lusitanian Basin), respectively. The main contribution of this study is the survey of the static (source, reservoir, and sealing rocks, in addition to traps) and dynamic elements (tectonic, migration, thermal, and diagenetic processes) of the two studied petroleum systems, seeking to understand the reasons for the success and failure of the analyzed reservoirs in relation to the accumulation of hydrocarbons. The following materials were used for this study: lithostratigraphic charts, event charts of petroleum systems, interpreted 2D seismic reflection lines, lithological profiles, outcrop data, geochemical analysis of source rocks, petrographic analysis, and description of diagenetic processes, which acts in the reservoir rocks. The methodology presents two phases: the first with a multiscale characterization of the elements of petroleum systems and economic aspects, and another with an integrated analysis of the reservoir potentials, based on the efficiency analysis table of the petroleum system elements and interpretative diagrams of the petroleum system elements. The occurrences of hydrocarbon accumulations indicate that the structuring of the Recôncavo Basin in horsts and grabens provides the formation of efficient migration routes, combined with an excellent source rock, reservoirs with good permo-porous characteristics, and effective seal rocks. On the other hand, in the Lusitanian Basin, the Paleozoic source rocks occur in mini-basins, with little lateral continuity, which negatively affects the generation of hydrocarbons. Besides this fact, saliferous tectonics were the main cause of hydrocarbon migration along faults or their walls towards the upper strata and to the surface. The fluvial reservoir rock shows a strong action of diagenetic processes, which affects its petrophysical properties. The main implication of this work is its contribution to the analysis of analogous reservoirs, based on the detailed investigation of the static and dynamic elements of petroleum systems.