FLOW UNIT DISTRIBUTION AND RESERVOIR MODELLING IN CRETACEOUS CARBONATES OF THE SARVAK FORMATION, ABTEYMOUR OILFIELD, DEZFUL EMBAYMENT, SW IRAN

H. Rahimpour-Bonab^1*, H. Mehrabi¹, A. Navidtalab¹ and E. Izadi-Mazidi²

¹ Department of Geology, Faculty of Science, University of Tehran, 14176-14411 Tehran, Iran.

² Geological Operation Office, Karoon Industry Area, N.I.S.O.C.,  Ahwaz, Iran.

* author for correspondence, email:  rahimpor@khayam.ut.ac.ir; or hrahimpor@gmail.com

Carbonate sediments within the Mid-Cretaceous Sarvak Formation form an important reservoir at the Abteymour oilfield in the western Dezful Embayment, SW Iran. The poroperm characteristics of this reservoir were controlled by factors including deposition under tropical climatic conditions and early diagenesis, repeated phases of subaerial exposure due to local, regional and global-scale tectonism, and diagenetic modification during burial. From microfacies analysis, the Sarvak Formation carbonates in the Abteymour field were interpreted in a previous study as having been deposited on a homoclinal ramp-type platform. Three third-order sequences were recognized in the middle Cenomanian to middle Turonian part of the formation. The reservoir quality of the carbonates was enhanced both by dissolution (comprising separate phases of eogenetic and telogenetic meteoric dissolution) and dolomitization (especially stylolite-related dolomitization).

In this paper, a rock/pore type approach was used in order to integrate petrophysical data with facies and diagenetic models within a sequence stratigraphic framework. Two different rock-typing methods for the determination of flow units were considered. Hydraulic flow units (HFUs) were identified firstly using flow zone indicators and secondly using a stratigraphic modified Lorenz plot. The flow units resulting from these two methods are compared, and their close correspondence within the sequence stratigraphic framework is discussed. In addition, the previously-used large-scale reservoir zonation scheme for the Abteymour field is correlated with the defined flow units, and four new Integrated Reservoir Zones are introduced. By integrating geological information with petrophysical parameters (including porosity, permeability and saturation) within a sequence stratigraphic framework, field-scale variations and controls on reservoir quality are described.

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