Sedimentary Environment and Sequence Stratigraphy of the Kangan Formation in Kish Gas Field (Kish Well A1 Subsurface Section)

Abstract

Kangan formation is one of the most important gas reservoirs of south and southwest Iran which it belongs to Dehram group and its age is Lower Triassic (Scythian). It was formed in an extensional basin in the expanded Neotethys Ocean. The basin was formed as a result of the Late Permian continental drift between Cimeria and Gondwana. The Kangan Formation is mainly composed of dolomite, dolomitic limestone with shale and anhydrite. It is unconformably underlain by the upper Permian Dalan formation and is conformably overlain by the upper Triassic Dashtak formation. In order to study facies, sedimentary environment and sequence stratigraphy in the Kish gas field, subsurface section of well A1 have been studied. Based on microfacies analysis, three facies belts include Tidal flat (A), Lagoon (B) and Shoal (C) were recognized in the Kangan formation. Facies analysis and those comparisons with modern and ancient environments indicate that the Kangan formation was deposited in an inner part of a homoclinal ramp platform. The sequence stratigraphy studies on the Kangan formation in this gas field led to assessment of three main sedimentary sequences of the Third-order in the Kish Well A1. The boundary between the Third-order sequences with each other and also the boundary between Third-order sequences with Dashtak formation were unconformity boundary of type 2 (SB2) and the boundary between Third-order sequences with Dalan formation which is the Permian-Triassic boundary is an unconformity boundary of type 1 (SB1). The main diagenetic processes in this formation are dissolution, cementation, micritization, anhydritization, dolomitization, recrystallization, physical and chemical compaction which played a significant role in improving reservoir quality. The dominantly ooid grainstone facieses with intercrystalline, moldic and Fracture porosity comprise the main reservoir facies of the Kangan Formation. Keywords: Dehram Group, Homoclinal Ramp, Kangan Formation, Scythian, Sequence Stratigraphy, Unconformity Boundary