Relationship between clay mineralogy and thermal maturity of Neogene-Quaternary shales in Ras El-Barr well, offshore Nile Delta, Egypt

Abstract

The basin of the Nile Delta contains a thick section of Neogene-Quaternary strata that have different values of thermal maturity as determined by vitrinite reflectance. The study area in the eastern part of the offshore Nile Delta basin is represented by the Ras El-Barr well No.1. Clay mineralogy, the half-width of the 10Å illite and 7Å chlorite peaks, and the A H values (area under peak/peak height) are systematically related to thermal maturity. The most important changes in clay minerals with increasing depth of burial are the regular reduction of expandable layers and the gradual increase in the crystallinity of illite and chlorite (decrease of the half-width value) with depth. The results of this study suggest that, in the absence of vitrinite, the values of the half-width of the 10Å peak and the A H value of illite (especially glycolated) may be used to quantitatively estimate the levels of thermal maturity and consequently as indicators to differentiate source rocks above and below the oil generation threshold and to approximate the hydrocarbon generation and preservation stages of potential source rocks.