FLOW UNIT CHARACTERISATION IN THE PERMIAN-TRIASSIC CARBONATE RESERVOIR SUCCESSION  AT SOUTH PARS GASFIELD, OFFSHORE IRAN

A.H. Enayati-Bidgoli*, H. Rahimpour-Bonab*⁺ and H. Mehrabi*

* School of Geology, College of Science, University of Tehran, Tehran, Iran.

⁺ Corresponding author, email: hrahimpor@gmail.com; rahimpor@ut.ac.ir

The South Pars gasfield (offshore southern Iran) has been investigated in detail in recent studies in terms of depositional, diagenetic and reservoir properties of the Permian-Triassic carbonate succession. In the present paper, a variety of flow unit approaches were applied to identify reservoir (flow) and non-reservoir (baffle or barrier) units within the Permian-Triassic carbonates. The zonation scheme was based on three approaches; (i) flow units were identified using the stratigraphic modified Lorenz plot (SMLP) method; (ii) hydraulic flow units were identified using a parameter known as the flow zone indicator (FZI); and (iii) petrophysical flow units (PFUs) were determined using the pore throat radius (R₃₅) and water saturation (S_w) parameters. Studies of flow units at both macro- and micro-scales showed that flow properties were controlled by both depositional and diagenetic features. In order to construct a reservoir flow model, the flow units and PFUs were correlated between the four wells studied within a sequence stratigraphic framework. SMLP-derived flow units appeared to be distributed homogenously within the reservoir succession resulting in a layer-cake architecture. By contrast, the FZI-derived hydraulic flow units drew attention to the presence of small-scale heterogeneities within the reservoir. A comparison between these methods showed that the flow model derived from PFUs included greater vertical and horizontal heterogeneities, especially in the Upper Dalan Member (upper K4 reservoir unit).  This was due to depositional/diagenetic heterogeneities in both lateral and vertical directions, and the parameters applied in the PFU method. The PFU-derived flow model showed a closer relationship to the actual reservoir performance than the flow units derived by the other methods and can therefore be used as the basis for future dynamic flow simulation.

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