Efeito da composição mineral e orgânica na petrofísica de folhelhos negros

Effect of mineral and organic composition on petrophysics of black shales

Abstract

A new landscape for the expansion of the global energy matrix has emerged with the exploration of unconventional resources derived from rocks whose petrophysical characteristics do not allow extraction through traditional methods. Among these rocks, black shales stand out as reservoirs with high hydrocarbon generation potential, although they exhibit complex properties. This study evaluates the black shales of the Araripe Basin through basic and advanced petrophysical tests, as well as material characterization techniques, to understand the effect of mineral and organic composition on the petrophysical properties of this type of rock. The results indicate that these shales are predominantly composed of minerals such as calcite and feldspar — a mineralogical composition that favors hydraulic fracturing, an essential technique for enabling hydrocarbon production in unconventional systems — and also contain high levels of organic matter. The samples exhibit low permeability but considerable porosity, although much of it is formed by micropores, mainly present in the organic matter and clay minerals. The analysis of the relationship between porosity and elastic wave propagation velocity revealed the important role of microporosity, which is mainly responsible for the elastic impedance contrast between the unconventional reservoir and host rocks in that basin, favoring the application of the seismic method for mapping this important type of hydrocarbon reservoir.