Effects of depositional and diagenetic characteristics on carbonate reservoir quality; a case study from the South Pars gas field in the Persian Gulf

The largest non-associated gas reserve of the world is hosted by the Upper Dalan-Kangan (Upper Khuff equivalent) Permo-Triassic carbonate-evaporite successions. Detailed characterization of these strata in the South Pars Field has shown that the reservoir properties are a function of both sedimentary and diagenetic processes at the field scale. Facies analysis of the studied units indicates that the sediments were deposited in the inner regions of a homoclinal carbonate ramp and were subsequently subjected to shallow diagenesis and minor burial. The vertical distribution of the facies shows cyclic patterns that impact reservoir quality. The rock type classes have been grouped on the basis of the dominant pore spaces, and have enabled distinct fields to be identified. This approach has demonstrated a relationship between poroperm values and rock type groups. Diagenetic overprinting has significantly affected the reservoir properties. Although the original poroperm heterogeneities in the studied reservoir are inherited from the Upper Dalan-Kangan paleoplatform, they have been modified strongly by diagenetic overprinting. Consequently, tentative correlation may be possible between facies types and reservoir properties based on diagenetic effects. Therefore, for precise characterization of the Upper Dalan-Kangan Reservoir properties it has been necessary to integrate both the depositional history and diagenetic features.