A qualitative-quantitative approach for studying the impact of facies and diagenesis control on the rudist biostrome of the Sarvak formation, Abadan plain, SW Iran

Abstract

Carbonate reservoir properties and their heterogeneities are of the main issues in reservoir qualitative and quantitative studies. In this paper, the role of facies and diagenesis processes on reservoir quality in the Cenomanian-Early Turonian Sarvak formation of SW of Iran was studied using 1504 samples from the core and a set of full suite logs from three wells. The depositional setting ranges from grain-rich reefal to lagoonal facies with grain-dominated and mud-dominated textures. Several diagenetic realms such as meteoric vadose, phreatic (vadose and marine) and mixing were identified based on petrographic observations. Compared to the mud-dominated facies of the Sarvak formation, the grain-dominated facies were intensely subjected to diagenetic processes. Furthermore, dissolution and neomorphism resulting from the subaerial exposure during meteoric diagenesis enhanced the reservoir quality, while further cementation, compaction and micritization have a negative impact on reservoir characteristics. The quantitative approaches show the eustatic sea-level rise in the Cenomanian-Turonian and the regional Turonian unconformity provide a textural and diagenetic pathway towards enhancing/reducing the reservoir quality. Reservoir properties are highly dependent on the sedimentary processes of the Rudist biostromes where secondary diagenetic agents are probably contributed through the selective leaching of aragonitic grains and matrix under the meteoric water environment.