Application of attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) to evaluate impact of rock heterogeneities on hydrocarbon distribution in deltaic reservoir sandstones

Abstract

Hydrocarbon functional groups distribution have been analyzed on 1*1cm grid on sample surfaces using ATR-FTIR spectroscopy to determine hydrocarbon bond type variation and factors controlling it. Micropermeability measurements have been carried out to determine relationship between absorbance of hydrocarbon functional groups and permeability. The main hydrocarbon functional groups recorded in the samples are the aliphatic C-H and aromatic C=C-C bonds. The aromatic functional groups are more concentrated in the silt-dominated laminations of the laminated sandstones and burrows in the bioturbated sandstones compared to the sand-dominated laminations and nonburrowed zones respectively. Textural, structural and bioturbation induced heterogeneities that influence pore size and permeability distribution in the samples is found to be the main factor controlling distribution of hydrocarbon bonds. In samples that lack any form of macro scale heterogeneities, hydrocarbon and permeability distribution are found to be random. High permeability generally correlates negatively with absorbance of hydrocarbon bonds and vice versa.