3D geological model for each reservoir unit comprising the Yamama Formation revealed to that the formation is composed of alternating reservoirs and barriers. In Subba and Luhais fields the formation began with barrier YB-1 and four more barriers (YB-2, YB-3, YB-4, YB-5), separated five reservoirs (YR-A, YR-B, YR-C, YR-D, YR-E) ranging in thickness from 70 to 80 m for each of them deposited by five sedimentary cycles. In the Ratawi field the formation was divided into three reservoir units (YR-A, YR-B, and YR-C) separated by two barrier units (YB-2 and YB-3), the first cycle is missing in Ratawi field.   The study involves 1 well in Luhais field (Lu-12), 3 wells in Subba field (Su-7, Su-8, and Su-9), and 5 wells in Ratawi field (Rt-3, Rt-4, Rt-5, Rt-6 and Rt-7), the Luhais, Subba, and Ratawi fields located in the Mesopotamia zone (Zubair subzone). The reservoir units (YR-C and YR-D) in Subba oil field, and YR-B in Ratawi oil field represent the major reservoir units that characterized by the best Petrophysical properties (the highest porosity, the lowest water saturation, and the best Net Pay Thickness), Luhais oil field has poor to moderate Petrophysical properties and low oil bearing in YR-A, YR-B and YR-C units, and produce heavy oil and salt water from YR-D and YR-E as indicated by low resistivity log reading, and according to the Drill Steam Test (DST) with the description of cutting in final geological reports.

This research deals with the study of the types and distribution of petrographic microfacies and Paleoenvironments of Mishrif Formation in Halfaya oil field, to define specific sedimentary environments. These environments were identified by microscopic examination of 35 thin sections of cutting samples for well HF-9H as well as 150 thin sections of core and cutting samples for well HF-I. Depending on log interpretation of wells HF-1, HF-316, HF-109, IIF-115, and IIF-272, the sedimentary facies were traced vertically through the use of various logs by Petrel 2013 software in addition to previous studies. Microfacies analysis showed the occurrence of six main Paleoenvironments within Mishrif succession, represented by basin, slope, shoal, Rudist biostrome, back shoal, and lagoon. Mishrif Formation was divided into six reservoir units depending on well logs and CPI. These units are separated by low porosity and high-water saturation of barrier beds. The reservoir beds from top to bottom are MA, MB1, MB2, MCI, and MC2. The reservoir units MB1, MB2, and MCI are the most important in the field of interest due to good reservoir properties and being the principle oil-bearing units in Mishrif Formation.

AbstructThis paper includes studying the microfacies evalution of Mauddud Formaion in four wells . Seventy-seven(77) sampels were collected of above mentioned wells. Based on fossil content of the samples under study, four main microfacies were identified: packstone , wakestone , grainstone and lime mudstone microfacies ,which deposited in shallow open marine and restricted marine environments. Petrographic examination of thin section indicated that diagenesis vary in intensity from one site to another, such as dissolution, cementation, compaction, dolomitization and micritization, which led to the improvement and deterioration of porosity. The dominant pore types are vuggy, interparticle and intercrystal.The lithology, mineralogy and the matrix were determined by using crossplot method, which showed that the predominant lithology of the formation is limestone with the presence of dolomite in very few percentages and the mineralogy is calcite. Based on the relationship between porosity and permeability the resevoir performance of the microfacies classified into four types: bad, fair, good and very good. Based on petrophysical properties and core description of well study Mauddud Formation was divided into four rock units A,B,C and D , in terms of reservoir, units A and C are considered good ,while B and D are bad. Keywords:Mauddud

The Microfacies analysis of the Cretaceous Mishrif Formation was studied in Nasiriyah oil field in Nasiriyah Governorate, southern of Iraq using integrated borehole data set that included, core samples and well logs in newly drilled well to analyze the microfacies and the Diagenesis Process of the formation, 100 thin sections for selected well. The results show that the formation composed of: (top to base) a fine-grained, limonitic fresh water limestone containing Charophytae. Four facies’ associations were distinguished in the Mishrif Formation. These include: - These include: - Restricted shallow Open Marin environment is represented by Wackstone and Mudstone to Wackstone. The shallow open marine environment is represented by bioclastic wackestone and packestone, as well as rudistid floastone in rare situations. Shoal Environmentis represented by bioclastic packstone to grainstone, as well as rudstone. Deep Marine environment is represented by mudstone to packstone. six diagenetic processes affected on Mishrif Formation: Cementation, Micritization, Recrystallization, Dissolution, Compaction and Pressure Solution (Stylolization), and Dolomitization, found in thin sections.

Abstract-