Flow Units Identification of the Sarvak Carbonate Reservoir, a Case Study from an Oil Field, SW Iran

The Sarvak Formation is one of the most important carbonate reservoirs of Iran. This study presents an integrated geological and petrophysical reservoir characterization of the Sarvak Formation in a giant oil field in the Abadan Plain, SW Iran. On the basis of porosity-permeability data, core description and petrographic studies from two key wells, flow units were identified and interpreted. To identify flow units within the Upper Sarvak Formation, three different petrophysical methods including (1) Flow Zone Indicator (FZI), (2) Pore Throat Radius (R35) and (3) stratigraphic modified Lorenz plot (SMLP) were applied. The results indicate that the FZI and R35 methods cannot efficiently discriminate the different reservoir zones and flow units for this reservoir, because of the high changes in petrophysical properties have mainly inherited from the internal geological heterogeneity. In contrast, SMLP method successfully classifies the studied reservoir into discrete flow units by considering the relationship between petrophysical properties and depositional and diagenetic features. From depositional facies point of view, the best flow units are related to talus, shoal-biostrome and shallow open marine depositional facies, while lagoon and distal open marine commonly show low reservoir quality. In low reservoir quality units, calcite cementation and compaction are the dominant diagenetic processes, while dissolution is the main agent for enhancing of the reservoir quality in the reservoir units with high quality. The results indicate that the interpretation of flow units based on the depositional and diagenetic characteristics provides the crucial insight on distribution of reservoir zones within the heterogeneous carbonate reservoirs, such as, the Sarvak Formation.