Sarvak Formation with Albian-Cenomanian age is one of the major oil producing units in the Zagros Basin. In the studied wells, Sarvak is about 637 meters thick and can be divided into two parts in ascending order: the lower part is 257 meters and is composed of interbedded fine grained limestone with pelagic fauna and shale and the upper part is 380 meter thick and consists of dolomitized neritic limestones with interbedded of fine grained limestones. Based on petrographic (207 thin-sections of cutting) and petrophysical studies of well logs, the effects of dolomitization on reservoir characteristics of the sarvak Formation have been evaluated. According to crystal size and shape as well as presence of dolomite in different lithofacies, three types of dolomite have been identified. Type one is fine grained (5-60 microns) that has formed at the early stage and type two is medium grained (60-250 microns) and type three is coarse grained (250-500 microns) that both of them formed the burial at the later stage of diagenesis. Based on petrography and well log analysis, the second type dolomite has increased the quality (porosity and permeability) of the reservoir rocks in this field.

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