Depositional facies, diagenetic overprints and sequence stratigraphy of the upper Surmeh reservoir (Arab Formation) of offshore Iran

Abstract

This study uses petrography, stable isotopes, petrophysics and wireline logs to constrain depositional facies, diagenesis, reservoir quality and sequence stratigraphy of the late Jurassic Upper Surmeh Formation (Arab Formation), in one of the northern Persian Gulf oil fields.Petrographic studies led to discrimination of nine microfacies which represented supratidal, intertidal, lagoon and shoal sub-environments of a carbonate ramp. In the un-cored wells five electro-facies were distinguished using Hierarchical Cluster Analysis (HCA) method. These electro-facies were correlated with the microfacies in a well which had both cores and logs data. Reservoir quality of the facies was determined by porosity and permeability data available from the cores.Among recognized diagenetic phenomena, fracturing, dissolution and dolomitization had an enhancing effect, but cementation, anhydritization and compaction had a deteriorating effect on reservoir quality. Stable isotope data were used to decipher the dolomitization process which is the most effective diagenetic process on the reservoir quality.For temporal and spatial reservoir quality prediction, the studied formation is investigated in the sequence stratigraphic framework. In this regard, four 3rd order sequences were determined which include a deepening-up transgressive systems tract (TST) in their lower part and a shallowing-up highstand systems tract (HST) in their upper part. Correlation of the identified sequences with those of equivalent formation in the Arabian plate is carried out to discuss the order of sequences and their major controls.