Microfacies Evaluation of Mauddud Formation in Ratawi Field, South Iraq

Abstract

This paper includes studying the microfacies evalution of Mauddud Formaion infour wells(Rt-2, Rt-5, Rt17 and Rt-19). Seventy-seven(77) sampels were collectedof above mentioned wells. Based on fossil content of the samples under study, fourmain microfacies were identified: packstone , wakestone , grainstone and limemudstone microfacies ,which deposited in shallow open marine and restrictedmarine environments. Petrographic examination of thin section indicated thatdiagenesis vary in intensity from one site to another, such as dissolution,cementation, compaction, dolomitization and micritization, which led to theimprovement and deterioration of porosity. The dominant pore types are vuggy,interparticle and intercrystal.The lithology, mineralogy and the matrix weredetermined by using crossplot method, which showed that the predominantlithology of the formation is limestone with the presence of dolomite in very fewpercentages and the mineralogy is calcite. Based on the relationship betweenporosity and permeability the resevoir performance of the microfacies classifiedinto four types: bad, fair, good and very good. Based on petrophysical propertiesand core description of well study Mauddud Formation was divided into four rockunits A,B,C and D , in terms of reservoir, units A and C are considered good ,whileB and D are bad.