Sedimentological review of upper triassic (Mulussa F formation) in Euphrates-Graben Syria

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Mulussa F formation is one of the important geological formations constituting the Mulussa group in Syria. The objective of this research is to review of sediments Mulussa F formation. Its deposits contain almost 50% of hydrocarbon potential through Euphrates Graben. Boreholes data permitted confining the formation between two Lithostratigraphic markers and enabled its division into three Lithostratigraphic members MUF3, MUF2, MUF1 (from bottom to top). Each member consists of a set of units, subunits and lithologic intervals. Petrology studying provides a precise petrological description of various formation members and their Digenetic. Results show that the members of the structure are composed of continental detrital sediments made up of clay stones (Kaolinite/Illite) and Shale/Dolomitic clay stone, covered by intervals of quartz sandstones, clay sandstones and silt sandstones. The carbonate sediments are absent from the formation unless it's base which consists of Dolomitic clay stone and its top which are close to carbonate composition. This sediment of those members spread out as repeated or harmonic alternations whose faces gradients reflect transgression and regression sequences. Due to the historical value of Mulussa F formation, it is vital to investigate its sediments status. The study of these sediments leads to represent narrow barriers near river mouth with meandering channels and limited coastal deposits.

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... Additionally, the definitions of the tectonism, regional unconformities, erosion processes, zonal geometries and distribution of the Upper Triassic and the Lower Cretaceous sediments along the graben area have proven to be very critical to the geometrical integrity of the geological and geophysical models. In the static geological models of the Upper Triassic and the Lower Cretaceous sediments over the Euphrates graben fields, the thickness changes and zonal distribution of the reservoir layers of these sediments are mainly controlled by faults, erosion, and the regional unconformities complex [Yousef et al., 2016]. ...
... The Upper Triassic Mulussa F sediments consist mainly of flood plain claystones interbedded with mostly medium to fine grained fluviatile sandstones. Lagoontype and shallow marine dolomitic claystone and dolomite interbeds are present in the lower part of the formation section [Yousef et al., 2016]. The Upper Triassic Mulussa F sediments are deposited conformably on the top of the Mulussa E sediments, and no sedimentary break is suggested by the available datasets at the time of the study. ...
... The Lower Cretaceous Rutbah sediments along the Euphrates graben area are subdivided into two zones from bottom to top (Lower Rutbah and Upper Rutbah, respectively), according to Spectral Gamma Ray logs and lithology compositions (see Fig. 6), [Yousef et al., 2016[Yousef et al., , 2017[Yousef et al., , 2018. The Lower Cretaceous Rutbah sediments are partially or completely eroded due to the influence of the BKU unconformity, which leads to high variations in the thickness and zonal distribution along the graben area. ...
We have investigated the tectonic and erosion features of the Upper Triassic (Mulussa F Formation) and Lower Cretaceous (Rutbah Formation) sediments in the Euphrates graben area and analysed their influence on changes in the thickness and zonal distribution patterns of these sediments. In this study, the geological modeling software of Petrel Schlumberger is used to model the regional geological structure and stratigraphy from the available geological and geophysical data. The Upper Triassic and Lower Cretaceous sediments (in total, almost 800 m thick) are the major hydrocarbon reservoirs in the Euphrates graben, which contain approximately 80 to 90 % of the total hydrocarbon reserve in this area. These sedimentary zones experienced variable changes in thickness and zonal distribution due to erosion processes caused by the two major regional unconformities, the Base Upper Cretaceous (BKU) and Base Lower Cretaceous (BKL) unconformities. The maximum thickness of the Upper Triassic sediments amounts to 480 m in the central parts of the Euphrates graben and along the NW-SE trend, i.e. in the dip direction of the Upper Triassic Mulussa F Formation. Towards the NE flank of the graben near the Khleissia uplift and the SW flank near to the Rutbah uplift, the thickness of the Upper Triassic sediments is gradually decreased due to their partial or total erosion caused by the BKL unconformity, and also due to a less space for sediment accumulation near the uplifts. The thickness of the Lower Cretaceous sediments increases in the northern, NW and NE flanks of the graben. Their maximum thickness is about 320 m. The BKL unconformity is the major cause of erosion of the Lower Cretaceous sediments along the southern, SE and SW flanks of the graben. In the Jora and Palmyra areas towards the NW flank of the Euphrates graben, the Upper Triassic and Lower Cretaceous sediments show no changes in thickness. In these areas, there was more space for sediment accumulation, and the sediments were less influenced by the BKL and BKU unconformities and thus less eroded.
... (Fortuny et al., 2015), which was deposited in a lagoonal shallow marine carbonate environment during the Late Triassic age (Ziegler, 2001). In northwestern Syria the Mulussa-F (Serjelu) Formation is relatively dissimilar in facies than Baluti Formation by consisting of clay and siltstone with little carbonate deposited in a fluvial and lagoonal environment (Yousef, Al-Kadi, & Morozov, 2016) and marked the beginning of a regional transgression that continued through to the Early Jurassic (Brew, Barazangi, Al-Maleh, & Sawaf, 2001). 4. Following Dunham's (1962) classification, and detailed microscopic investigation, three main microfacies were identified in the Baluti carbonates in the studied section, which are grouped into one basic type of facies association relating to their environmental interpretation of a subtidal-semi-restricted lagoon. ...
A detailed sedimentological investigation of the Baluti Formation (Late Triassic) in the Warte section, Imbricated Zone, northeastern Kurdistan region of Iraq has been undertaken for the first time. The formation is comprised of 34 m of dolomitic limestone, marly limestone, and marly dolomitic limestone which is partially brecciated and all interbedded with shale and several beds of marl in the lower part. Based on the field observations and petrographic inspections, four different lithostratigraphic units were identified in the studied section, which are, in ascending order: marly dolomitic limestone interbedded with marl and shale unit, brecciated marly dolomitic limestone interbedded with shale unit, fractured marly dolomitic limestone unit, and marly limestone interbedded with shale unit. The petrographic study of 19 thin sections of Baluti carbonates shows that the majority are composed of carbonate mud (micrite). The skeletal grains include ostracods, calcispheres, benthonic foraminifera, gastropods, bivalves, clasts, and bioclasts. While non‐skeletal grains include peloids, intraclasts, and extraclasts. The results of X‐ray diffraction (XRD) of five samples and scanning electron microscope (SEM) of three samples of the shale and marl of the studied formation show that the main clay mineral is illite, whereas non‐clay mineral is dolomite. The carbonate rocks of the Baluti Formation were subjected to different diagenetic processes, such as micritization, dolomitization, cementation, compaction, solution, pyritization, neomorphism, and fracturing. Three main microfacies were identified in the Baluti carbonates and according to their environmental interpretation, they are grouped into one basic type of facies association—subtidal‐semi restricted lagoon. Field observation, petrographic, microfacies, and textural analysis indicate that the Baluti Formation in the Warte section was deposited in a shallow marine, subtidal (lagoon) environment with semi‐restricted conditions.
This article presents the results of cementation characteristics and their effect on sandstone reservoir quality of the Upper Triassic Mulussa F, the Lower Cretaceous Lower Rutbah, and the Upper Cretaceous Post Judea Sandstone formations in selected fields in the Euphrates Graben area, Syria. This study emphasises the role of cementation in the evaluation of the diagenetic history of the sediments, developing effective porosity, as well as evaluation of reservoirs stimulation procedures and potential for formation damage of the sandstone reservoirs. Quartz cement is present as well developed tabular or pyramidal syntaxial overgrowths. Kaolinite cement is present as vermicular aggregates which are most abundant within sandstones of the Mulussa F Formation. Carbonate cements include siderite and dolomite. Four lithofacies were identified within the studied formations; lithofacies-1 and 2 correspond to fluvial depositional environments, lithofacies-3 and 4 correspond to fluvial to estuarine channel environments. The Post Judea Sandstone and the Lower Rutbah reservoir units are typically lithofacies-3 sequences in which quartz overgrowths are the dominant cement. Because the total cement is more extensive in the Post Judea Sandstone Formation than in the Lower Rutbah Formation, resulting in high porosity (up to 26%) and permeability (6 000 mD), the reservoir quality is predicted to be best in the Post Judea Sandstone Formation. The reservoir units in the Mulussa F Formation contain the highest cement volumes comprised of early siderite and kaolinite, which, with the development of compaction-resisting quartz overgrowths and resultant compactional pore volume loss, has resulted in typically lower porosity being preserved than in the Lower Rutbah and Post Judea Sandstone formations.
Results of this study are based on core materials description, thin sections, Cathodoluminescence (CL), and Scanning Electron Microscope (SEM) examinations. The Lower Cretaceous over the Euphrates Graben area was characterized by carbonate sedimentation in shallow marine environments. The low energy lagoonal to inner shelf sediments of the Judea Formation includes micritic mudstone to wackestone texture, dolomitic limestones and dolostones. Two types of dolomites recognized in the carbonates of the Judea Formation, the preserving microcrystalline dolomites which commonly founded in the partially dolomitized micritic limestones, and the destructive coarsely crystalline dolomites which commonly founded in the dolostones and dolomitic limestones. Petrographic examinations indicate that the preserving microcrystalline dolomites represent subtidal cycles developed in a shoal to open marine depositional environments, they probably formed under conditions of the shallow burial diagenesis. The destructive coarsely crystalline dolomites may develop in more basinward, open marine environments under conditions of the deep burial diagenesis that accompanied by rising in temperature, pressure, and burial depth. It is believed that evolution of the diagenetic history of the Judean Formation sediments occurred in two diagenetic stages; the shallow burial diagenesis, and the deep burial diagenesis. Compaction processes, early fracturing, micritization, early calcite, and the early phase of dolomitization were part of the multiple diagenetic alterations during the shallow burial diagenesis. The deep burial diagenesis was marked by dissolution, late stage of dolomitization and replacement, mechanical and chemical compaction, and the late calcite precipitation. It is believed that dolomitization of the Judea Formation carbonates in the Euphrates Graben has contributed to improving the reservoir properties by increasing the porosity and thus the permeability.
The dolostones and dolomitic limestones of the Lower Cretaceous Judea Formation are a key target of hydrocarbons in most of the Euphrates Graben fields. Core materials investigation, thin sections petrographically examinations, and petrophysical evaluations were obtained to determine enhancement of the porosity through dolomitization. Results showed that the lagoon-shallow marine carbonates of the Judea Formation are subdivided into two main zones; the upper “Limestone Zone” is micritic limestones dominated with no reservoir potential, and the lower “Dolomite Zone” is dolomitic limestones and dolostones dominated with good to very good reservoir potential. Dolomitization of the mudstones and wackestones of the micritic limestones resulted in formation of microcrystalline dolomicrite and early fabric destructive dolomites. Conversely, dolomitization of the packstones and grainstones resulted in formation of the fabric destructive and saddle dolomites. Based on petrography data, dolomitization of the “Limestone Zone” is interpreted by the seawater dolomitization mechanism at low-temperatures, while dolomitization of the “Dolomite Zone” is interpreted by the burial dolomitization mechanism under high temperature and pressure conditions. The “Limestone Zone” is characterized by the poorest reservoir quality, while the “Dolomite Zone” is characterized by the best reservoir quality. The seawater dolomitization did not significantly enhance the porosity, while the burial dolomitization contributes to enhancing the preserved secondary porosity. Stylolites microfractures and dissolution seams associated with dolomitization played as major factors in porosity enhancement of the dolostones and dolomitic limestones and serving as pathways for hydrocarbon migration. Dissolution processes increased the porosity and more permeability unless they are filled with the precipitated dolomite and/or calcite. Calcification had significant effects on the porosity by blocking the cavities and channels and decreased the effective pore volume.
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