Influência da composição mineral e fluida sobre as propriedades petrofísicas de folhelhos negros, estudo de caso: Bacia do Araripe

Abstract

Shale deposits are the main sources of oil and natural gas, because they contain the organic content that, under special conditions, originates hydrocarbons. The main technique used in the oil industry for the discovery of hydrocarbon deposits is reflection seismic, although there have been great advances in both acquisition and processing, and in this there have been errors in predictions regarding lithology. Low velocity shales, often due to their shale generator condition, have been erroneously interpreted as being reservoirs composed of porous sandstones saturated with hydrocarbons. The petrophysical properties, especially the elastodynamic properties, are affected by variables such as mineral composition, state of tensions, geometry (size and shape) of grains and pores, fluid saturation and quality of the contacts between the mineral grains. In order to characterize mineralogy, four samples of the Araripe Basin were selected, which were tested by x-ray microtomography (μcT), two of these samples also undergoing x-ray nanotomography (ncT) assays. The analysis of the mineral composition of the black shales of the Araripe Basin showed that the DRX, μcT and ncT methods are complementary and the comparison of their results assists in the decision on mineral fractions that present a more difficult recognition.