Electrofacies modeling as a powerful tool for evaluation of heterogeneities in carbonate reservoirs: A case from the Oligo-Miocene Asmari Formation (Dezful Embayment, southwest of Iran)

Abstract

The Asmari Formation comprises carbonate successions in the east and southeast of the Dezful Embayment, SW Iran. Besides, this Formation has undergone complicated diagenetic events. The Asmari reservoir shows high variation in quality and hydrocarbon production across the Bibi Hakimeh oilfield. Contrary to core data, petrophysical well-logs are almost available for all drilled wells in the oilfield. Therefore, electrofacies (EF) clustering was applied to divide well-log data into distinct clusters with individual petrophysical and geological attributes using Multi-Resolution Graph-based Clustering (MRGC) method. For the definition of diagenetic rock classes (DR), in which both depositional and diagenetic textures have been contributed, the main diagenetic modifications were analyzed in all sedimentary facies belonging to various depositional environments to know whether depositional environments have played a controlling role in reservoir heterogeneities of the Asmari Formation. The quality of electrofacies clusters was evaluated using the distribution of diagenetic rock classes and porosity-permeability data through these clusters. This study reveals that diagenetic rock classes, in which dolomitization and touched pores have prevailed, are more consistent with high-quality electrofacies, while low-quality electrofacies clusters are characterized by dense and cemented matrix together with some isolated pores. As a result, the reservoir heterogeneities of this reservoir have been widely controlled by diagenetic modifications, while depositional environments provided the required circumstances for domination of these modifications within each sedimentary facies. Finally, geostatistical modeling of electrofacies clusters reveals that domination of dolomitization and touched pores, as a consequence of dolomitizing fluids, together with microfracture systems improved reservoir quality of western/northwestern and central parts of the oilfield.