Dolomitization and burial history of lower triassic carbonate reservoir-rocks in the Persian Gulf (Salman offshore field)

Abstract

Shallow marine carbonate sedimentation prevailed during the Early Triassic in the northern part of the Persian Gulf (Kangan Formation; offshore Iran). Associated near surface and (to a lesser extent) burial diagenesis had significant impacts on the evolution of reservoir properties of the Kangan Formation. In some Iranian offshore fields such as Salman, pervasive, early dolomitization of the Kangan carbonate rocks is believed to have played an important role in improving the reservoir characteristics of this unit. Detailed petrographic and geochemical analyses indicate that such dolomitization could be explained by means of the sabkha/seepage-reflux model. Furthermore, three types of dolomites, found in Kangan rocks in the Salman Field, have been described: (1) fabric-retentive, (2) fabric-destructive, and (3) cement. Fabric-retentive dolomites are the most frequent commonly found in the studied field, with respect to the other types. Oxygen and carbon-stable isotopic analyses confirm that the fabric-retentive dolomites and associated anhydrites formed at surface and near-surface conditions, whereas the fabric-destructive dolomite formed at temperatures above 50 °C. The burial history of the Salman Field is divided into three major phases (tectonic quiescence and low subsidence rates, and two active phases with high subsidence rates). The fabric-retentive dolomites are mostly related to the first phase, while the fabric-destructive and dolomite cements are related to the second and third phases including shallow and deep burial, respectively.