Impacts of Depositional Facies and Diagenesis on Reservoir Quality:A Case Study from the Rudist-bearing Sarvak Formation,Abadan Plain,SW Iran

An integrated geological-petrophysical analysis of the rudist-bearing sequence of the Cretaceous Sarvak Formation is given one giant oilfield,and provides an improved understanding of this main reservoir in the Abadan Plain,in the Zagros Basin,SW Iran.The main objective of this study is to evaluate reservoir potential of the Sarvak Formation,and then to utilize the calibrated well log signature to correlate reservoir potential in un-cored wells.Eight main facies are recognized and categorized in five facies groups:lagoon,shoal,rudist-biostrome,slope,and shallow open marine,deposited on a shelf carbonate platform.Given the distribution of diagenetic products and their effects on pore systems,three diagenetic facies namely,(DF-1)low dissolution and cementation;(DF-2);high dissolution;and(DF-3)high cementation are differentiated.The initial sedimentary characteristics in combination with distribution of diagenetic products play an important role in reservoir quality heterogeneity.The effect of diagenetic processes related to disconformities mainly depends on the facies nature below these surfaces.Grain-dominated facies of shoal and rudist debris,observed below the Cenomanian–Turonian disconformity,are mostly characterized by high dissolution and interconnected pore systems.Finally,depositional and diagenetic facies in the studied wells are correlated by petrophysical well log data,leading to distribution of the reservoir zones.Data obtained can be utilized for efficient reservoir characterization of the Sarvak Formation and its equivalent units in the Arabian Plate.

On the occurrence of Neoplanorbulinella Matsumaru, 1976(Foraminifera) from the late Oligocene of Central Iran(Qom Formation):Palaeobiogeographic implications

The shallow marine carbonates of the upper Oligocene Qom Formation yielded several occurrences of the foraminiferan genus Neoplanorbulinella Matsumaru. Neoplanorbulinella saipanensis Matsumaru has so far been recorded from the late Eocene-early Miocene of Japan and late Oligocene of NE Italy whereas N. malatyaensis Gedik is only reported from the Oligocene from its type locality in the Malatya Basin, eastern Turkey. The new records reported here from the Qom Formation indicate that both species occur in the Dobaradar section, ca. 10 km south of the city of Qom in North-Central Iran. The palaeogeographic distribution of these two species therefore has to be extended as far as the palaeolongitude of current Central Iran.The accompanying larger benthic foraminifers, including Miogypsinoides complanatus(Schlumberger),M. formosensis Yabe and Hanzawa, Spiroclypeus margaritatus(Schlumberger), Operculina complanata(Defrance), and Risananeiza pustulosa Boukhary et al., indicate the upper Chattian SBZ 23 Zone. The coexistence of the N. saipanensis and N. malatyaensis points to suitable palaeobiogeographic conditions of Central Iran to host Western and Eastern Tethyan taxa.

Stratigraphy of the Alveolina elliptica group from the Middle Eocene of Iran:Calibration with calcareous nannofossils biozones and description of Alveolina ozcani n. sp.

Precise taxonomy and the chronostratigraphic calibration of the Middle Eocene Alveolina from Central Iran is here undertaken from the Chah-Talkh section of the southern Sabzevar region(Central Iran). We have identified Alveolina kieli, Alveolina stercusmuris and Alveolina nuttalli along with the new species Alveolina ozcani n. sp. that we include into the Alveolina elliptica group. We have also found Nummulites uroniensis, Nummulites obesus and Nummulites cf. verneuili and associated calcareous nannofossils that look reliable to make thoughtful correlations with the Shallow Benthic Zones(SBZ). The foraminiferal biostratigraphy suggests an assignment to the upper part of the lower Lutetian-lower part of the middle Lutetian,SBZ13(Middle Eocene), further strengthened through the identification of the calcareous nannofossil NP14b-NP15b or CNE8-CNE10 biozones, providing a solid correlation with the global stratigraphic standards.

Postmiogypsinella intermedia Sirel and Gedik 2011 from the upper Oligocene of Central Iran(Qom Formation):Paleogeography and paleoenvironmental implications

Postmiogypsinella intermedia Sirel and Gedik,2011 is reported for the first time from the shallow-marine limestones of the upper Chattian Qom Formation,Central Iran.This miogypsinid species has so far only been recorded from the upper Oligocene of Malatya(type locality)and Sivas(Central Anatolia)in eastern Turkey and from the upper Oligocene of the Prebetic Domain,SE Spain.The new record from Central Iran,paleobiogeographically located at the Eurasian margin of the Tethyan Seaway between the Western and Eastern Tethys realms,indicates that the paleogeographic distribution of this species has to be extended eastwards as far as Central Iran.This observation is not unexpected,since miogypsinid foraminifers with eccentric embryonic-nepionic apparatus(e.g.,Miogypsinella,Miogypsinoides,Miogypsina)are usually widely distributed.The accompanying larger benthic foraminifera,including Miogypsinoides complanatus(Schlumberger),Miogypsinoides formosensis Yabe and Hanzawa,Spiroclypeus margaritatus(Schlumberger),Operculina complanata(Defrance),and Risananeiza pustulosa Boukhary et al.,indicate the late Chattian age(corresponding to SBZ 23 Biozone).Postmiogypsinella intermedia is indicative of a shallow-marine middle ramp environment with oligotrophic conditions and inhabited the relatively deeper part of the photic zone.