Abstract The Sirt Basin is one of the youngest sedimentary basins in Libya and covers an area of approximately 600.000 km² in north central Libya. It is located on the northern margin of the African plate, with approximate coordinates 14°00`- 20°00`E and 28°00`-31°00`N. The Late Jurassic-Early Cretaceous as Sarir Sandstone in the Sirt Basin evolved as a consequence of the interplay between global eustasy and regional tectonics. As Sarir Sandstone of the eastern Sirt Basin is composed mainly of sandstones and shales resting unconformably on a basement complex of igneous and metamorphic rocks. It is unconformably overlain by the Upper Cretaceous sediments of Maragh, Lidam and Etel formations. It has been subdivided into three members. The upper member consists mainly of sandstones with intercalations of siltstones and shales of variable thickness. The middle member consists of shale and silty shale. The basal part of the formation, which rests directly on the crystalline basement represents the lower member. It is comprised of sandstone with subordinate intercalations of siltstones and shale. Two main facies have been recognized on the basis of lithological features and types of stratifications: which consist mainly of shale and intercalation of silt and sand. The Middle Shale Member consists mainly of shallow lake deposits, containing black shale facies. Continental Fluvial Deposits represent most of the cored interval and it belongs to the Upper as Sarir Sandstone. These facies have been subdivided into braided and meandering lithofacies: The braided depositional system, has been recognized in three different intervals of the studied cores; classified as subfacies (1), subfacies (2) and subfacies (3). The meandering depositional system, represents three sub-environments including point bars, abandoned channels and over-bank deposits. The reservoir characteristics of these sediments are studied on the basis of porosity, permeability and reservoir zonation. The reservoir quality of As Sarir Formation is largely controlled by primary sedimentary features associations, which were shaped by the depositional environments. Meandering Lithofacies are formed from continuous sand successions and show good porosities, up to 18.51%, and permeabilities up to 125.5mD. The Braided Lithofacies also show good reservoir quality, but the effective porosity and permeability are lower, because of associated shales. The most important diagenetic features responsible for a reduction in reservoir quality are those resulting from compaction, cementation, and the diagenesis of clay minerals.
صلاح الدين محمد الوحيشي (2014)

Abstract The Sarir Sandstone in Messla Oil Field are of Lower Cretaceous ageAptian Alpian and occur in the subsurface of the eastern part of the Messla high in the southeast Sirt Basin. The Sarir Sandstone interpret as fluvial and alluvial fan deposits whereas the Lower Sarir Sandstone were deposited in a braided system as inter-channel bars. The Upper Sarir Sandstone were deposited in the meandering belt of the fluvial system. The Sarir Sandstone is on-lapping Formation and wedge out against Rakb Group. The Sarir Sandstone is unconformable overlies the Pre-Cambrian Basement and unconformable overlain by the Upper-Cretaceous Rakb Group where it is pinching (wedging) out against the Bald Basement; Messla High)). Lithostratigraphic correlations of borehole logs ((well logs)) in concession 65 suggests that deposits gradually downed a fault controlled topographic surface increased in thickness on the down-thrown side of a fault controlled the topographic surface of Pre-Upper Cretaceous Unconformity. IV M. Sc. Hassin Haweel “Sedimentological Aspects of the Sarir Sandstone in Messla Oil Field”, 2015 Core Samples record mainly sandstone units interbedded with sandstone and shale and minor streaks and the Red Shale Unit. Estimation of depositional environment has thus been made from grain size analyses using thin sections. Petrographic studies show that the Sarir Sandstone in composition from (subarkose to arkosic arenite). The Sandstones range from texturally immature to submature, however, much of the clay content is diagenetic in origin and not a function of the depositional regime. Diagenetic studies reveal a gnite complex paragenesis. During early diagenesis, the Sarir Sandstones were modified by Calcite, dolomite, and locally pyrite, diagenesis process; replacements of corroded silica by carbonates. Cementation fluvial sandstones Intrastratal dissolution and precipitation of kaolinite in the resulting pore space. Deformation of micas between more resistant grainy pre-dates one phase of quartz overgrowth, probably the carbonates.The purpose of this study was to investigate in detail the characteristics of the Sarir Sandstone in Messla Oil Field. Another aim was to find out the relation to the adjacent area. The method of this study was conducted with the review of the previousworks in Messla Oil Field; published papers, the open file of the Arabian Gulf Oil Company (AGOCO), well files for the data to be used in constructing maps, cross sections and profiles. Four cored wells (418 feet) V M. Sc. Hassin Haweel “Sedimentological Aspects of the Sarir Sandstone in Messla Oil Field”, 2015 were used for the core descriptions and cut samples that represent the Sarir Sandstone and (130) thin sections were used for the Petrographic analysis with polarized and scanning electron microscopes (SEM). On the other hand, XRD and XRF were not available. The results of the study were: Subsurface investigations including cores (conventional and side walls), petrographic analysis, and wire-line logs suggested that this formation (Sarir Sandstone) can be divided in to three main units in Messla Oil Field; these units are: The Lower Sarir Sandstone, the Red Shale, and the Upper Sarir Sandstone. In the adjacent area Sarir Formation was divided in to five members; Pre-Upper Cretaceous Member-1 unconformably overlying Pre-Cambrian Basement, and upwards; Member 2, Member 3, Member 4, and Member 5 unconformably overlain by Rakb Group. The Lower Sarir Sandstone in Messla Oil Field is characterized by the presence of gravely sandstone, gradually changes in to the Red Shale. Also, from the core descriptions plotted sheets, and the well logs it is finning upwards. The quarzitic sandstones of (the Lower and the Upper Sarir Sandstones) are considered to be the main producing horizons where quartz grains have undergone a complex diagenetic history, including: Authigenesis, quartz and feldspar overgrowths, dissolution, carbonates cementation, and replacement. The principal conclusion was that: the gravelly sandstone unit at the Lower part of the Lower Sarir Sandstone was deposited, most likely in a braided system as inter-channel bars. The sandstone unit of the Upper Sarir VI M. Sc. Hassin Haweel “Sedimentological Aspects of the Sarir Sandstone in Messla Oil Field”, 2015 Sandstone was deposited in the meandering belt of the fluvial system. The shale facies of the Red Shale unit represents a well-developed break between the Lower Sarir Sandstone and Upper Sarir Sandstone units; it also provides a good seal for the underlying sandstone of the Lower Sarir Sandstone. The nature of the shale facies, (i.e. lack of organic content, and presence of oxidizing conditions indicated by iron oxides color, indicate that they are not a significant source of hydrocarbons. On the other hand, the Rakb Shale isthe only source rock in the studied and adjacent areas.
حسين محمد علي حويل (2015)

Abstract The study area is located in and around Umm Ar Razam village, about 50 Km east of Darnah city, north-eastern Libya. In this study many claystone sections were studied. These claystones belong to the lowermost part of Al Faidiyah formation of Upper Oligocene – Lower Miocene age. The studied sections consist of claystone beds ranging in thickness about 10 meters. These bentonitic clays are generally grey to greenish grey in colour, with popcorn – like appearance. They have a waxy character and are exposed sporadically in this area as isolated outcrops. They might be deposited in lagoonal, lacustrine or shallow marine environment. The main purpose of this thesis is to study the origin and to evaluate the Umm Ar Razam bentonitic clays. For example, lithology, mineralogy, the chemical composition, crystal forms and habits, physical properties, industrial uses and treatment will be investigated. The Results showed that these clays consist of the minerals Na- montmorillonite, Kaolinite, and Illite. Non – clay minerals includes quartz, calcite, dolomite, gypsum, halite, muscovite, rutile, sanidine, and tridymite. Moreover, clay mineral fraction studies using the different techniques showed that these bentonitic clays were formed due to in situ alteration of volcanic ash in subaquous environment. Evidences for such an occurrence include mineralogical evidence as the existence of high temperature minerals as sanidine, rutile, and tridymite. The existence of unaltered volcanic ash as seen from SEM photomicrographs also supports this origin. Furthermore, XRF results showed downward depletion of silica right below these bentonitic clays 6 in calcarenite beds of Al Abraq formation. XRF results also showed that the Umm Ar Razam bentonites are in accordance with the American bentonites and the parent material of such bentonites came from basic volcanic ash materials. In addition, the viscosity and the filtration of Umm Ar Razam bentonite is nearly identical with the international bentonite by adding (Soda Ash) and (Na2 SiO3 ) with special treatment method. The cost of the Enhanced Umm Ar Razam bentonite is less than of the imported bentonite cost. Based on the physical and chemical properties these bentonites can be used in many industries especially as building materials and drilling fluids.
فيصل عياد أبو سهمين (2009)