The role of fracturing and mineralogical alteration of basement gneiss in the oil exhsudation in the Sousa Basin (Lower Cretaceous), Northeastern Brazil

This work focuses the geological context of an oil sample obtained from an exhsudation in a superficial well, located at Salguinho Farm, Sousa Basin, at the central Borborema Province, Brazil. It is a light oil, with 81,1% of saturated compounds and a predominance of C17 and C23 n-paraffins, in which biomarkers point out to a non-biodegraded mature oil. Although the source rocks of this oil are unknown, the reservoir are metamorphic rocks from the basement, in a structural arch nearside the depocenter area of the basin. This lithology corresponds to ortho-derived gneiss strongly modified by ductile and brittle deformation (fracturing), as well as mineralogical alteration due to retrometamorphic and hydrothermal reactions. Here we emphasize and discuss the importance of such modifications underwent by the gneiss in the development of a propitious porosity and permeability for the further oil accumulation.