Reservoir properties distribution in the framework of sequence stratigraphic units: A case study from the Kangan Formation, Iranian offshore gas field, the Persian Gulf basin

Abstract

The Lower Triassic Kangan and Upper Permian Dalan Formations have large volumes of gas and condensate reservoirs in the southern part of Iran and nearby countries. Shallow carbonate and evaporate succession of the gas bearing Kangan Formation in the Salman field was deposited in a shallow water carbonate ramp. The Salman field is a shared structure from which two-thirds is owned by Iran and the remaining portion is under territories of United Arab Emirates (UAE). The Kangan reservoir is traditionally subdivided into K2 and K1 zones. However, it has been divided into two depositional sequences based on the integration of seismic data criteria which are supposed to be a third-order sequence. In this study, the relationship between depositional sequences and reservoir properties have also been investigated. This paper mostly aims at finding and documenting the relation between depositional sequences and reservoir properties as well as constructing the related 3D geological model. Using and comparing three-dimensional (3D) seismic data and five well data particularly petrographic studies allow the recognition of 9 microfacies and two 3rd order sequences which are part of the Permian–Triassic Khuff Formation. In this study, three-dimensional models of sequences framework were constructed based on seismic and well data. Moreover, porosity and water saturation property models have constructed considering the sequence stratigraphic framework. According to the models, the high reservoir quality units mainly consist of grain-dominated rock fabrics, which are associated with shoal facies developed in the Late TST (transgressive system tract) and Early HST (highstand system tract). These results indicated high energy conditions in the transgressive sea-level rise. The supratidal, intertidal and lagoonal facies, presenting anhydrite and mud dominated rock fabrics showing a lower reservoir quality developed in the Late HST and Early TST. Therefore, the reservoir quality of HST is lower than TST. The reservoir quality of K2 is also much better than K1 and it is considered as the most prolific pay zone in the South Pars gas field. Based on the findings, the sequence stratigraphy framework in reservoir characterization plays a significant role in the better understanding of reservoir quality as well as reservoir property modeling.