The role of burial history in the evolution of the porosity of sandstones in brazilian marginal basins

Abstract

A new parameter - the time-depth index - is defined and applied to a quantitative and empirical investigation of the influence of burial history on the evolution of sandstone porosity in some basins of the Brazilian continental margin (i. e., the Santos, Campos, Espírito Santo, Cumuruxatiba, Recôncavo, Sergipe-Alagoas, and Potiguar). The time-depth index for a reservoir is calculated based on burial history diagram. It is equivalent to the area enclosed by the reservoir burial curve and the axes of the diagram. Used in conjunction with textural and compositional characterizations, the concept explains the main variations m the porosity of sandstones in the basins studied, which makes it a useful forecasting tool. The reservoirs presenting the best porosity values are those that display better grain sorting, greater quartz contents in terms of detrital composition, and smaller time-depth indices.