Reservoir rock typing using integrating geological and petrophysical properties for the Asmari Formation in the Gachsaran oil field, Zagros basin

Abstract

The Gachsaran oilfield is one of the largest oilfields in the Zagros basin and the Asmari Formation is a primary reservoir rock in it. In this study, the reservoir rock typing has been carried out by a combination of microscopic (microfacies and diagenesis) and petrophysical (electrofacies and hydraulic flow units) studies. Microscopic studies of 478 thin sections from core samples led to identification of 11 microfacies belonging to 4 facies belts including tidal flat, lagoon, shoal, and open marine as well as diagenetic phenomena such as micritization, bioturbation, neomorphism, compaction, dissolution, cementation, dolomitization, and anhydrzation. In order to determine the rock types, the effects of diagenesis on distribution of porosity-permeability data in the petrophysical diagram were investigated and eventually 12 geological rock types introduced. Concepts of electrofacies and hydraulic flow units have been used to determine the petrophysical rock types and then their propagation in non-cored depths and wells. In this context, by means of the well logging data cluster analysis in the Paradigm ™ Geolog 6.7.1 software, 4 electrofacies were determined and modeled. The validity of these electrofacies was examined through their correlation with 12 geological rock types, core porosity-permeability data, and capillary pressure curves. Furthermore, by using core porosity-permeability data, the flow zone indicators were calculated and accordingly 6 flow units identified in the framework of discrete rock types. Subsequently we tried to validate these flow units by using estimation of permeability for each of them and their comparison with core permeability, and also correlating flow units with capillary pressure curves. Finally, in order to predict the flow zone indicators and propagation of the flow units in the non-cored depths and wells, modeling of flow zone indicators was carried out by establishing a quantitative relation between calculated flow zone indicators and well logging data in the software. The results of this research can be useful for hydrocarbon development and production in the future of this oilfield and similar fields.