The purpose of this study is to identify the pore types and distinguish the pore facies based on the diagenetic performance. The petrographic examination of 230 thin sections lead to the identification of a variety of primary and secondary porosities and show that the vuggy, moldic and intercrystalline pores have more frequency than the intraparticle, interparticle and fenestral pores. The plot of data obtained from thin sections on the ternary porosity graph used for determining the pore facies and their diagenetic trends and led to the identification of6 pore facies including depositional (PF1), moldic (PF4), and vuggy (PF6) pore facies, and also mixture pore facies PF2 (mixture of PF1 and PF4), PF3 (mixture of PF1 and PF6) and PF5 (mixture of PF4 and PF6). The comparison of petrography results with the well logs, core permeability and the calculated RQI and FZI values show that the pore facies which have touching pores, especially PF6 and PF1, have played the most important role in improving the quality of the reservoir, especially in the upper part of the studied zone. Also the pore facies which have separate pores, especially PF4, have the most influence in the reduction of reservoir quality relative to other pore facies, especially in the lower part of the studied zone. Most of the pores identified in the studied zone are the secondary porosity and diagenetic in origin. This demonstrates that the reservoir characteristics in the studied zone have been strongly modified by diagenetic overprinting. The most important diagenetic processes affecting the pore systems of the Asmari reservoir are cementation, selective and massive dissolution and dolomitization. Massive dissolution plays the most active role in the formation of touching vugs as well as enhancement of reservoir quality. Cementation and fabric selective dolomitization play the most active role in decrease of the reservoir quality.

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