Effect of diagenesis on the petrophysical properties of the Miocene rocks at the Qattara Depression, north Western Desert, Egypt

Abstract

This study focuses on the effect of diagenetic processes on the petrophysical characteristics of the Miocene rocks exposed east of the Qattara Depression, north Western Desert, Egypt. Several techniques were applied on the collected rock samples in order to determine their mineralogic composition and the diagenetic processes they have undergone. The petrophysical analyses are conducted on horizontal plugs representing the Miocene Formations in the study area. They mainly include porosity, permeability, and density. Petrographic analysis revealed that the Moghra Formation is composed mainly of quartzarenites with few shale and limestone intercalations. The Marmarica Formation, on the other hand, is composed mainly of sandy dolomicrite, sandy biodolomicrite, and sandy biomicrite facies. The main diagenetic processes encountered are neomorphism, dolomitization, dissolution, cementation, compaction, and replacement. Values of porosity, permeability, grain, and bulk densities for the studied plugs derived from the Moghra Formation range from 14.7 to 27.8 %, from 0.01 to 35.39 mD, from 2.51 to 2.79, and from 2.01 to 2.32 g/cm3, respectively, while they range from 2.9 to 40.8 %, from 0.002 to 14739.15 mD, from 2.67 to 2.8 g/cm3, and from 1.62 to 2.65 g/cm3 for the samples of Marmarica Formation. Both petrographical and petrophysical studies revealed primary and secondary origins of the sample porosity and permeability and that the studied sandstones can be considered as good hydrocarbon reservoirs. In addition, the studied carbonate rocks are characterized by high effective porosity and permeability due to the secondary enhancement through the dissolution of fossils and other components implying that their corresponding subsurface occurrences represent good reservoir rocks. © 2016, Saudi Society for Geosciences.