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Mauddud Formation (Albian stage-the Early Cretaceous) is an important oil reservoir in Ratawi field of southern Iraq. Four wells, R T-2, R T-3, R T-6, and R T-7, located 70 km northwest of Basra, were selected to study microfacies properties and petrophysical associations with the probability of oil production. Seventy-seven core samples are collected, and thin sections for petrographic analysis. The self-potential, Gamma-ray, resistivity, and porosity logs are used to determine the top and bottom of the Mauddud Formation. Water saturation of the invaded and uninvaded zones, shale volume, and porosity were calculated. The study area results showed that the quantity of shale is less than 15% for most of the wells, and the dominant porosity is the secondary porosity. In contrast, the primary porosity is low in all study wells, and the formation contains varying proportions of producing hydrocarbons. The results suggest the formation comprises light-colored dolomitized lime and pseudo-oolitic white limestone with green to blue-gray shale. The petrographic analyses of 65 thin sections of the Mauddud Formation reveal that most skeletal grains are shallow marine-derived faunas, while non-skeletal grains include peloids and ooids. The facies analysis showed that the Mauddud Formation was deposited within different sedimentary environments ranging from deep to very shallow environments, which was represented by a large variation in Five microfacies and ten submicrofacies, the microfacies "Mudstone, wackestone, packstone, grainstone, and Rudstone "submicrofacies" Peloidal wackestone to packstone, Bioclastic wackestone to packstone, Miliolids wackestone to packstone,Orbitolina wackestone, Peloidal packstone to grainstone, Orbitolina packstone, Mudstone to wackestone,Bioclastic wackestone, Miliolids and Bioclastic wackestone to packstone, Bioclastic packstone, and Peloidai grainstone". This variance suggested that the formation might be deposited within the carbonate platform's variety of environment, such as "deep sea, restricted, shallow open marine, mid-ramp, rudist biostrome, and shoal." Seven different kinds of pores have been found in the carbonate sideman of the Formation: Interparticle, Intraparticle, moldic, Vuggy and fracture.

A petrographic and microfacies analysis was conducted to understand better the sequence development of Shiranish Formation in Mergasur area within Erbil governorate (Lailuk section), Northern Iraq. These analyses interpreted the depositional environment, an essential aspect of stratigraphic analysis. Shiranish Formation is overlying Bekhme Formation in Lailuk region, with an unconformable contact. Shiranish series consists of four main microfacies: lime mudstone, wackestone, packstone, and grainstone. These microfacies are further divided into seven sub-microfacies: planktonic foraminiferal lime mudstone, planktonic foraminiferal lime mudstone to wackestone, planktonic foraminiferal wackestone, bioclastic planktonic foraminiferal wackestone, bioclastic planktonic foraminiferal wackestone to packstone, planktonic foraminiferal packstone, and planktonic foraminiferal packstone to grainstone. The sub-facies are associated with four discrete depositional settings: profound shelf, abyssal or cratonic deep basin, incline, and the inclined base. The studied region, Shiranish Formation, contains three asymmetrical depositional sequences (A, B, and C). The sequence disparity suggests a correlation between sea level and carbonate production variation. Asymmetrical cycles represent a phase of increasing sea level after a calm period. Shiranish sequence was formed over a discontinuous surface, creating a clear distinction from the underlying Bekhme Formation. The surface is represented using a type two-sequence boundary (SB-2). the Shiranish succession in the research region is created in an area of high subsidence. A significant transgression caused by a series of sea level occurrences resulted in the formation of the Shiranish Formation on a carbonate platform with significant subsidence. A significant transgression that caused several periods of sea level rise and stillstand is responsible for the formation of the Shiranish Formation on a carbonate platform that has seen significant subsidence. The depositional sequence stratigraphy, Shiranish sequences A to C, is distinguished by three maximum flooding surfaces (MFS-165, MFS-170, and MFS-175). These sequences have a notable correlation with comparable stratigraphic patterns reported in Iraq and other regions of the Arabian plate.

One of the oil field's main reservoirs is the Mishrif Formation, which is found in the Nasiriyah oilfield in the southern part of Iraq (Late Cenomanian-Early Turonian). It was one of the three oil wells selected for this study. To extract various petrophysical parameters for open wells indicated by gamma ray, density, neutron, self-potential, acoustic, and resistance, a variety of well logs were analyzed. The qualitative interpretation of the logs allowed for the identification of different types of rocks, the boundaries and thicknesses of the strata, the depths of the formation, and the zones that contained water and hydrocarbons. The quantitative interpretation, which assesses the reservoir's attributes by computing its porosity, the quantity and distribution of the shales, the levels of water and oil saturation, and other elements, that are necessary to evaluate the reservoir’s units in the research wells. The features of the study wells and the used logs were reported, to make clear how these features were distributed among the sample wells. The collected petrophysical characteristics were handled and shown as charts. There are two types of units within the Mishrif Formation: reservoir-containing CR-I, MA, CR-II, and MB. In most wells, reservoir units are made up of hard, low-porous rocks that are positioned between highly porous reservoir units. For a few wells, the MA unit had low residual and mobile hydrocarbon percentages, whereas the MB unit had large percentages, while the hard rocks had significant percentages of water saturation.

The Nahr Umr Formation, which is Albian-Early Turonian in age, was investigated in the Nahr Umr Formation succession at two wells of the Luhais oil field in southern Iraq. The study defined sedimentary facies, types, and distribution of porosity and their relationship to sedimentary facies, as well as different types of diagenetic processes. It also included the distribution of facies in the Nahr Umr Formation in relation to suggested depositional settings. Thin sections of the cores from the two chosen boreholes (Lu 39 and Lu 43) in the Luhais Oil Field were used to study the petrography and lithofacies of the Nahr Umr Formation. The five fundamental facies identified in this study are poorly and well-sorted, quartz arenite sandstone, in additional to clayey sandstone poorly sorted, sandy shale, and shale, it represented many sub-environments present in the delta plain depositional environment, the distributary channel depositional environment, and the delta front depositional environment. The Nahr Umr succession in the examined wells (Lu -39 and Lu-43) in the Luhais oil field, southern Iraq, has three asymmetrical cycles of the third order, which are identified by the variable frequency as well as the symmetry of the relative sea level. They show successive events involving sea-level rise and stillstand. In the study area, the succession is formed by surface erosion, which represents the boundary of the sequence type 1 (SB1) distinguished in all wells of the study. As a result of the significant drop in the relative sea level during the stage of the marine retreat (regressive), which indicates coarsening-shallowing upwards and with continuous decreasing, a sequence boundary of type 2 (SB2) is formed at the end of this tract. The boundary of SB2 represents the decrease in sea level, indicating the beginning of the second stratigraphic sequence, which shows the deposition of sand in the river channels as it reflects progressive accretion patterns towards the basin represented by (MFST. Then the sediments begin to thin, and the shale layer appears at the Nahr Umr Formation top, which reflects the regional marine progress and marks the sedimentation of the limestone formation that separates it from the Nahr Umr Formation on the regional flood surface.

The Mishrif Formation is an important succession that was deposited during the Cenomanian–Early Turonian. More than 79 thin sections of core in addition to well log data for the Mishrif Formation from 2 boreholes within the E oilfield (E-1, and E- 2) were used to determine the different associations facies to interpret the depositional environment of the Mishrif Formation. Six major microfacies were diagnosed the Mishrif Formation, Mudstone, Wackestone, Packstone, Grainstone, Boundstone, and Rudstone and ten submicrofacies include: Bioclastic Packstone submicrofacies with rich Echinodermat, Coral and Rudist fragment and high Dolomitization, Rudstone submicrofacies with large Rudist fragment and vug porosity , Boundstone submicrofacies with very large coral, Plankton Foraminiferal Packstone submicrofacies withe Globigerinelloides and Calcispheres, Bioclastic Wackestone to Packstone submicrofacies with dolomite and calcareous algae, Peloidal Packstone with coral, pillites, pieces of Rudist and Separate-Vug pore, Bioclastic Packstone to Grainstone submicrofacies, Peloidal to Bioclastic Packstone submicrofacies, Benthonic Foraminiferal Mudstone submicrofacies, Rudist fragmented Mudstone. These microfacies were deposited in restricted, shoal, shallow open marine, rudist bioherm, and deep marine environments.

A surface section of the Fatha Formation (Middle Miocene) was studied in the Shaqlawa area, Erbil, Northern Iraq. It consists of siliciclastic silt, evaporates, and carbonates in a mixed siliciclastic silt composition. The Fatha Formation in the study area can be divided into two members of variable thickness based on rocky differences. Depositional settings ranged from shallow open-marine and restricted-hypersaline to supratidal and continental (sabkha, fluvio-deltaic, and exposure). It is bounded below by a type one sequence boundary above the Eocene Pila Spi Formation and marked by conglomerates. The upper sequence boundary with the Injana Formation is conformable. Thirteen sedimentary facies were distinguished in the Fatha Formation within the Shaqlawa region of northern Iraq and include sandstone to mudstone, wavy bedded sandstone to mudstone, Flaser bedded sandstone to mudstone, Marl, sandstone, cross lamination sandstone, Trough cross bedded sandstone, Planar cross bedded sandstone, marly limestone lithofacies, bioclastic grainstone to packstone microfacies, bioclastic lime mudstone to wackestone microfacies, lime mudstone-wackestone microfacies, and gypsum lithofacies. The depositional environment of the formation was inferred based on the facies association concepts. The succession formation can be divided into several third-order cycles, which reflect fluctuations in the relative sea-level rise. High-frequency cycles of transgressive System Tract and Highstand System tract. Fundamental to the evolution of the sequence, in this case, is the local tectonic component.