S Parham; M.R Kamali
Abstract
The Dalan upper member is a gas reservoir in the Persian Gulf, which is important because of gas and condensates production. This unit has been affected by dolomitization. Dolomicrites is a type of dolomites identified in the studied interval. This investigation concentrates on dolomicrites from the ...
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The Dalan upper member is a gas reservoir in the Persian Gulf, which is important because of gas and condensates production. This unit has been affected by dolomitization. Dolomicrites is a type of dolomites identified in the studied interval. This investigation concentrates on dolomicrites from the point of view of its spatial distribution and reservoir zonation. This type of dolomite has been studied using thin section, RCAL, and isotopic analysis data. This type of dolomite is identified relying upon petrographical evidences such as very fine to fine unimodal, anhedral to subhedral crystals of dolomite. The texture is equivalent to xenotopic-A and nonplanar-A. Some features like fenestral fabrics, microbial filaments evaporitic cast, anhydrite nodules and mud cracks are also identified. The findings led us to the conclusion that dolomicrites pertains to fenestral dolomitic mudstone, which deposited in supratidal to arid upper intertidal. The result of isotopic analysis of oxygen revealed that this dolomite formed at temperature between 20.36ºC to 46.6ºC. This confirms deposition in sabkha environment so sabkha dolomitization model offered for dolomicrites. The diagenetic processes affected dolomudstones are dissolution, cementation, compaction, anhydrite replacement and fracturing.
Studies of the porosity and permeability data indicated that reservoir characterization is under the influence of texture. In mud-dominated facies like dolomitic mudstone, reservoir quality is poor to fair unless this part influenced by subsequent diagenetic processes like dissolution and fracturing.
S Parham; M.R Kamali
Abstract
The Dalan Upper member (Permian) with carbonates and evaporite interlayer is one of the most important gas reservoirs in the folded Zagros area and Persian Gulf. In this investigation porosity types, their genesis and controlling factors have been studied at Surmeh surface section and a subsurface section ...
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The Dalan Upper member (Permian) with carbonates and evaporite interlayer is one of the most important gas reservoirs in the folded Zagros area and Persian Gulf. In this investigation porosity types, their genesis and controlling factors have been studied at Surmeh surface section and a subsurface section in Persian Gulf. Based on the new genetic classification of Ahr (2008) for carbonate porosity, porosity is created or altered by hybrids of depositional processes, diagenetic processes and mechanical fracturing in the studied intervals. In subsurface samples, porosity is hybrid of depositional and diagenetic types. In grain-supported microfacies, like ooidgrainstone related to the shoal environment, interparticle porosity is created which is a type of depositional porosity. Moldic, vuggy and intercrystallineporosity, which are diagenetic types of porosity,were formed in the later stages of diagenesis. Therefore, porosity in this microfacies is facies-selective and facies map can be used as a proxy for porosity distribution map. In surface section, besides depositional and diagenetic porosity, fracturing and brecciation are also significant. Brecciationoccured as a result of dissolution of anhydrite of Nar Member and formed the solution collapse breccias. Active tectonic in the folded Zagros belt and folding are another possible sources of fracturing in the surface samples. The properm data of routine analysis shows that the reservoir characteristic of the studied interval is heterogeneous.So, it has been compartmentalized into six zones with different reservoir qualities from poor to very good.
