Tirgan formation of the Kopet-Dagh Basin (northeast Iran) represents one of the Urgonian carbonate platforms that were deposited during the Early Cretaceous time in the northern Alpine Tethys and ...deformed during the Alpine orogeny. In this study, six stratigraphic sections of the shallow-water platform sediments (Tirgan formation) were measured based on microfacies and fauna abundance. Detail study of petrography, fossil content, and sedimentary structures led to the identification of fifteen microfacies belonging to four facies belts including open marine, shoal, protected lagoon, and tidal flat. The sediments of the Tirgan formation exhibit calcareous green algae, abundant ooids, oysters, bryozoans, and crinoids in inner and middle platform ramp facies and planktonic bivalves and sponge spicules in outer-platform facies. Furthermore, the absence of basinal deposits and lack of evaporate evidence point to deposition under warm-temperate and humid climate conditions. Sequence stratigraphy analysis of Tirgan formation led to distinguish a single depositional sequence in all of the sections which are composed of transgressive and highstand systems tracts with sequence boundaries of type II (SB2). The lowermost lower Aptian Tirgan sequence in the study area relatively shows a similar trend in comparison with the global curve. This basin was deepened over time so that shaly and marly sediments of Sarcheshmeh formation were placed over Tirgan conformably and may suggest a drowning event that was likely related to unusual global warming. Last, this study contributes to the better understanding of the high distribution of facies assemblages in the Urgonian carbonate platforms.
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.
•We used, a combination of microscopic (12 rock types) and petrophysical studies (4 electrofacies and 6 hydraulic flow units), to reservoir Rock-Typing in the Asmari reaservoir.•Electrofacies and flow units modeling can be implemented on the field.•The results of this research can be useful in hydrocarbon development and production this field and similar fields.
