Alternativas para modelos de velocidades sísmicas dos rafts no Complexo de Marlim - Bacia de Campos - e os impactos na volumetria dos reservatórios do pré-sal

Abstract

Seismic velocity modeling is part of the seismic image building process, and the seis- mic images are the foundations for subsurface studies, having significant importance especial- ly when inserted in the structurally deformed geological contexts. In some regions of the Campos Basin, offshore Brazil, the sedimentary overburden above the pre-salt reservoirs sec- tion presents this structural complexity, mainly due to raft tectonics that laterally poses salt domes, carbonate rafts and siliciclastic sediments. This work is developed using nan available and extensive wells´ database, inserted in the Marlim Complex, which allowed seismic ve- locities analysis of the carbonate rafts, providing a general idea about the related impacts over the gross-rock volumetric estimations of the pre-salt reservoir package. The well data com- bined with a detailed seismic interpretation led to the proposition of seven alternative seismic velocity scenarios for the rafts, driving the uncertainties analysis regarding forecast of the pre- salt reservoir depth, as well as the volumetric variation of the rocks where hydrocarbons is inserted in. The geological motivations for each scenario are discussed providing a compre- hensive understanding of how the gross-rock volume may vary depending on the presence of these rafts as well as because the internal composition of the rafts. The resulting models are quantitatively compared in terms of depth predictions and gross-rock volume, which are some of the standard uncertainty metrics for decision making in the oil industry, particularly in re- gions where the well information is absent. The obtained results confirmed that the topogra- phy of pre-salt reservoirs can vary considerably, even in scenarios built from well data and geological constraints. The description of the reservoir topography impacts on several as- sumptions about the field subsurface interpretation, with consequences for the seismic geolog- ical exploration, characterization, development, and production of the pre-salt section.