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 Seven geological sections have been examined and sampled with emphasis on sedimentological & diagenetic processes within Abu Ghaylan Formation and the contact relationships with the underlying Abu Shaybah and overlying Kiklah Formations. Based on current detailed field loggings and microscope investigations, 10 facies are recognized within Abu Ghaylan Formation. The lowermost succession characterised by an overall transition from continental fluvially dominated deposits of the Abu Shaybah Formation into transitional to marginal marine, tidal flat deposits of the Abu Ghaylan Formation upward. The transitional nature of this lowermost part succession is demonstrated by interbeddings of claystone, sandstone and fossiliferous facies arranging in coarsening up cycle, in which most probably deposited in estuary / beach environment.The Abu Ghaylan Formation generally wedges laterally eastward and exposes intermittently east of Wadi Ghan area resulting of syngenetic uplift of Wadi Ghan area followed by erosion (ElHinnawy & Cheshitev, 1975). A slightly earlier uplift and greater erosion in a westward sloping basin of deposition near the close of the Early Jurassic and Early Cretaceous times is suggested by Fatmi & Sbeta (1991). The current study reveals that several exposure surfaces are demonstrated within Abu Ghaylan Formation suggesting uplifting and erosion episodes interrupted Abu Ghaylan Formation, where a restricted distribution of Abu Ghaylan may suggest a local tectonic overprint.Although the overall impression is that the base beds of Kiklah Formation starts with sandstone and red clay beds as channel infill deposits above Abu Ghaylan carbonate unit with surface of unconformity, however, based on current close investigation, a sequence characterized by interbeddings of carbonate and greenish clay overlying Abu Ghaylan Formation with surface of unconformity and gradationally overlain by sandstone beds should be introduced as separate unit attributes to Kiklah Formation.The current study emphasizes and supports a solution collapse origin for the breccias and introduces better insight into architecture and geomorphology of the breccias bodies that are exposed in the area of study. The dissolution of evaporites is considered responsible for all breccias development in this stratigraphic interval. According to the occurrence mode of breccias, the breccias intervals have been divided into two main parts; a lower section of strata that contains collapsed paleocaves and an upper section of strata that is deformed to varying degrees due to the collapse and compaction of the section of paleocave-bearing strata. The sharp flat base, inverse grading, V-shaped/ sag structures and irregular undulating top of brecciated bodies are recognized within Abu Ghaylan Formation and typically characterize solution collapse processes. Based on field study and architecture relationships, five distinctive karst facies are recognized in the area of study.The early diagenetic genetically related processes probably interrupted the deposition of Abu Ghaylan Formation is a most possible assumption for the origin and timing of breccias formation.
أحمد أبوبكر الحلو (2015)

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)