An Investigation of The Properties of Dolomicrites in The Upper Dalan Units in a Field in The Persian Gulf

Dalan upper member is a gas reservoir in the Persian Gulf which is important because of gas and condensates production. This unit is 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. In this investigation with the use of thin section study, RCAL data and isotopic analysis data, this type of dolomite has been studied. Relying upon petrographical evidences such as very fine to fine unimodal, anhedral to subhedral crystals of dolomite, this type of dolomite is identified. 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 is deposited in supratidal to arid upper intertidal. The result of isotopic analysis of oxygen revealed that this dolomite has formed at temperature between 20.36oC to 46.6oC. This confirms deposition in sabkha environment so sabkha dolomitization model offered for dolomicrites. Diagenetic processes affected on dolomudstones are dissolution, cementation, compaction, anhydrite replacement and fracturing. Studies of the porosity and permeability data indicate that reservoir characterization is under the influence of texture. In mud-dominated facie like dolomitic mudstone reservoir quality is poor to fair unless this part is influenced by subsequent diagenetic processes, like dissolution and fracturing.