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Abstract
Dalan Formation is one of the most important gas reservoirs of south and southwest Iran which it belongs to Dehram Group and its age is Middle to Late Permian. The Dalan formation is interpreted as reflecting a major tectono-eustatic event related to the onset of rapid thermal subsidence of the early Neo-Tethys passive margin in Arabia and Iran, and the drowning of its rift shoulders. The Dalan formation consists mainly of medium to thick-bedded oolitic to micritic shallow-marine carbonate, with intercalations of evaporates. This formation overlies the Faraghan formation and extends up into the Lower Triassic kangan formation. The current paper is focused on the facies, sedimentary environment and sequence Stratigraphy study of the Middle to Upper Permian Dalan formation in the West Assaluyeh gas field the subsurface section of well ASL-A. Based on microfacies analysis and significant founa and flora, nineteen major facies in five facies associations including Tidal flat (A), Lagoon (B), Shoal (C), Open marine (D) and Mid ramp (E) were recognized in the Dalan formation. Facies analysis and those comparisons with modern and ancient environments indicated that the Dalan formation was deposited inner to mid parts of a homoclinal ramp. The sequence stratigraphy studies on the Dalan formation in this gas field led to assessment of seven main sedimentary sequences of the third-order in the Assaluyeh field, well ASL-A. The boundary between the third-order sequences with the Faraghan formation and between the Nar and Upper Dalan members are Subaerial Unconformity (SU) and the boundaries between the third-order sequences with each other and also with the Kangan formation are Correlative Conformity (CC). The main diagenetic processes in this formation are dolomitization, dissolution, anhydritization, cementation and compaction which played a significant role in improving reservoir quality. The shoal ooid grainstone facies with intergranular and oomoldic porosity comprise the main reservoir facies of the Dalan formation.
Highlights
The hydrocarbon reservoirs of the Dalan formation in the Qatar-South Fars Arch contain some of the important gas reserves in the Middle East region, as well as the world [1] [2]
Gradual changes between relatively widespread facies belts, lack of breccias and turbidites, presence of high energy grainstones in shoreline environments associated with calcareous green algae and benthic foraminifera are indicative of homoclinal ramp setting
3) Restricted lagoonal facies are found in most part of Dalan formation especially in Nar and Upper Dalan members
Summary
The hydrocarbon reservoirs of the Dalan formation in the Qatar-South Fars Arch contain some of the important gas reserves in the Middle East region, as well as the world [1] [2]. Stratigraphic cross section of the Dalan formation measured at Kuh-e-Faraghan is the thickest section of this formation in northern Persian Gulf [3]. This formation is named after the Dalan anticline situated 110 kilometers S-SW of Shiraz. The current paper is focused on the facies, sedimentary environment and sequence Stratigraphy study of the Dalan formation in the Assaluyeh gas field the subsurface section of well ASL-A. The Qatar-South Fars Arch is a major regional anticline that runs through the central Persian Gulf and it has a northeast-southwest direction and extends southwards into the Qatar Peninsula. 2) Construct conceptual depositional model for facies distribution of the Assaluyeh gas field. 1) Characterize the facies and depositional environments and their stratigraphic distribution. 2) Construct conceptual depositional model for facies distribution of the Assaluyeh gas field. 3) Identify the major depositional sequences and construct a sequence stratigraphic framework based on stacking pattern, type of bounding surfaces which can be used to constrain stratigraphic architecture and reservoir layering
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