Reservoir Facies Development and Depositional Models of the Mixed Carbonate/ Clastic Asmari Formation in the Northern Margin of Dezful Embayment

Abstract

ABSTRACT The Oligo-Miocene Asmari Formation in the North Dezful Embayment of SW Iran is comprised of mixed carbonate/ clastic facies associations. The lower part of Asmari Formation is characterized by a variation of clastic facies and the upper part is dominated by carbonate shallow marine facies types. The main purpose is to investigate a regional reservoir facies changes (lateral and vertical facies variations) and also to define a relationship between sequence stratigraphy and reservoir facies quality among the three selected wells, which are located in the North magin of Dezful Embayment. During this case study, at least ten reservoir facies types were identified and classified in the study area using all available geological subsurface data. As well as, the six third-order depositional sequences (carbonate and clastic dominated cycles) have also been distinguished and correlated in the study area, representing particular sedimentary regime and relevant reservoir characteristics, which are controlled by local tectonic events and eustatic sea level fluctuations. Theses facies types directly make the significant aggraded to prograded systems tracts that can be separated by correlable surface boundaries, influenced by local disconformity events. The reservoir facies quality of these depositional sequences is drastically controlled by sedimentary regime, facies types and different diagenetic impacts on the reservoir. Local collisional tectonic events and relevant erosional features had a big role to influx the clastic sediments in the study area. The early and late diagenetic events generated the reservoir carbonate facies. The novelty of facies this case study is to define a new reservoir facies classification of the mixed Asmari reservoir stacks in the northern part of Dezful Embayment, which is affected by several influxes of the clastic sediments, multiple diagenetic events on the upper carbonate and tectonic events.