Stratigraphy and Palaeontology
Somayeh Baharlouei Yancheshmeh; Ebrahim Ghasemi Nejad; Hossain Rahimpour-Bonab; Seyyed Ali Aghanabati
Abstract
Permo- Triassic subsurface section at Lavan 3 Well in Lavan Gas Field exhibits a 85 m-thick succession of limy dolostone and dolomitic limestone bearing anhydrite in the upper Dalan Formation, as well as a 154 m-thick succession of limy dolostone and dolostone with anhydrite ...
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Permo- Triassic subsurface section at Lavan 3 Well in Lavan Gas Field exhibits a 85 m-thick succession of limy dolostone and dolomitic limestone bearing anhydrite in the upper Dalan Formation, as well as a 154 m-thick succession of limy dolostone and dolostone with anhydrite intercalations in Kangan Formation. In the present study, 116 species belonging to 55 foraminifera genera were identified which were divided into two biozones, namely Charliella altineri- Paraglobivalvulina mira- Dagmarita chanackchiensis Assemblage zone (Dzhulfian in age) and Claraia aurita- Spirorbis phlyctaena Assemblage zone (Anisian in age). Nine primary microfacies were identified in the upper Dalan Formation, while, 13 microfacies were detected in Kangan Formation, together with different sub-environments (sabkha, tidal flat, lagoon, submarine ridge, and open marine) which were found to be deposited in a shallow marine carbonate platform in the form of a homoclinal ramp. Based on microfacies changes, aggradational, progradational and retrogradational stacking patterns of deposits and by conformation with the Gama-ray log, these strata could be divided into a couple of third-order sedimentary sequences for the upper Dalan Formation, as well as a couple of third-orders for the Kangan Formation, including two system tracts (TST and HST). On a global scale, the findings are comparable to the upper part of the Absaroka supersequence.
R. Kadkhodaie-Ilkhchi; B. Nouri; R. Jodeyri
Abstract
The Upper Dalan and Kangan formations with the late Permian- early Triassic age are considered as the main reservoir rocks of some fields in the Persian Gulf. These formations with carbonate-evaporate interval are composed of shoal, lagoon and tidal flat facies deposited in shallow parts of a carbonate ...
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The Upper Dalan and Kangan formations with the late Permian- early Triassic age are considered as the main reservoir rocks of some fields in the Persian Gulf. These formations with carbonate-evaporate interval are composed of shoal, lagoon and tidal flat facies deposited in shallow parts of a carbonate ramp under the warm and arid climate condition. In these facies, dolomitization is a common diagenetic process which has been discussed in terms of the formation, distribution and its relationship with the reservoir quality. This process with regard to the original sedimentary properties, and also the effect of such diagenetic processes as dissolution and anhydrite cementation, has different effect on the reservoir characteristics. Dolomite has been mainly distributed as replacement with an insignificant part as cement. Fine crystalline replacive dolomites in mud dominated facies of tidal flats, have been formed by surface evaporation and pore water concentration in early diagenesis. In contrast, replacive dolomites in grain dominated facies, as fabric selective and non-fabric selective, have been developed by the effect of evaporate brines penetration during the burial diagenesis. In these facies, anhydrite has been formed as patchy and pervasive cement. Dolomitic facies with pervasive anhydrite, similar to fine crystalline facies of tidal flats, show low reservoir quality. Dolomitic facies with patchy anhydrite and also coarse crystalline replacive dolomites have higher reservoir quality. The results show that dolomitization when is associated with development of fabric destructive and coarse replacement dolomites, especially within the grain dominated facies, has an effective role on reservoir quality improvement.