TITLE:
Facies, Sedimentary Environment and Sequence Stratigraphy of Dalan Formation in South Fars, Iran —(Qatar-South Fars Arch) Well ASL-A
AUTHORS:
Nasser Rezavand, Davood Jahani, Hossein Asilian
KEYWORDS:
Facies, Sedimentary Environment, Homoclinal Ramp, Sequence Stratigraphy, Dalan Formation
JOURNAL NAME:
Open Journal of Geology,
Vol.6 No.8,
August
30,
2016
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.