المستودع الرقمي لـقسم الجيولوجيا

Abstract

As part of the NE-trending Mourizidie Shear Zone in south-central Libya (south of Mourizidie pass), four units representing Preccambrian basement rocks (metasediments) were mapped during field work: phyllites (metaclaystone); metapelites (metasiltstone); pasmmites (metasandstone) and Quartzites. Granitic bodies of various sizes (few meters to hundreds of meters) are found throughout the study area. The metasediments and granites are both intruded by veins and dikes having an overall NE trend. Four Palaeozoic sedimentary units were mapped within the study area. The concidence of the S1 foliation with the S0 of the original bedding of the protolith is a proof that the S1 foliation is caused by deep burial. The petrographic description of the minerals in thin section shows an assemblage of sericite, muscovite and biotite, all representing a sub-greenschist facies to greenshcist facies. This low grade metamorphism helped in preseving the original sedimentary structures of the protolith, thus helping in identifying the original bedding plane S0. Faults observed in the field or traced on aerial photograhs belong to three major trend: NE, NNE, and ENE. Folds are extremely diverse in shape, attiude and tightness, thus their classification is equally diverse. This diversity is observed in the field even within a distance of no more than few meters. The isostatic rebound of the basement could have caused this great difference in the attitude of the folds, especially at considerable depths characterised by a kinematically ductile, restricted and contained settingAt least two phases of deformation are present in the area. D1 is marked by the generation of S1, while D2 is marked by the first folding F1 caused by the isostatic rebound he generation of S2 foliation as fan cleavage is directly related to the F1 folding. Some folds underwent refolding, which lead to an F2 phase of folding.Sequential schematic structural model is proposed to explain the structural history of the study area. This model should be tested through intensive detailed field work large scale map in nearby areas.
مسعودة محمد حنبولة (2015)

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 area of study is located in the southeastern part of Block NC98 and is informally named C-Structure area, and it is completely situated in the center of Al Hameimāt Trough, South East Sirt Basin, Libya. The main reservoir rock in this structure is the Upper Nubian Sandstone Member, whereas the Reworked Sandstone Unit and Transitional Beds are considered as secondary reservoir rocks. These reservoirs are mainly composed of sandstone to argillaceous sandstone. The Upper Nubian Sandstone reservoir quality is adversely affected by volcanic rocks especially the thick intercalation of volcanoclastics within the Upper Nubian Sandstone. The Upper Nubian Sandstone Member was deposited during Early Albian times. The Reworked Sandstone Unit was possibly deposited in Cenomanian? to Turonian times and may be related to the overlying Transition Beds.Up to date, four wells have been drilled in this structure (C1-NC98, C2-NC98, C3-NC98 and C4-NC98) and were targeting the clastic reservoirs of the Upper Nubian Sandstone and/or overlying Upper Cretaceous Transitional beds and Reworked Sandstone unit. Only C1-NC98 and C2-NC98 wells have tested significant hydrocarbon in the Upper Nubian and Reworked Sandstone unit whereas C3-NC98 and C4-NC98 wells have tested no hydrocarbon in both reservoirs and are abandoned as dry wells. This study is aimed to validate the stratigraphical aspects, depositional environment and reservoir quality assessment in order to decipher the reasons of drilled dry holes. The obtained results are anticipated to provide valuable geological information for the current and future prospect evaluation in the area. All available wire line logs of C wells (C1-NC98, C2-NC98, C3-NC98 and C4-NC98) and adjacent wells have been used to correlate the stratigraphy of the Pre-Upper and Upper Cretaceous silisiclastic sediments in the area of study.Representative core samples across the reservoir rocks of the candidate wells have been laid down for core description. The acquired results have been integrated with conventional core analysis and petrographic results to investigate the lithofacies characterization and depositional environment in order to sub-divide them into different lithofacies.Different types of geological maps have been prepared in this research (e.g. stratigraphical/structural cross sections, subcrop maps, isobach maps, structure contour maps and etc.) to delineate the formation extension and correlation. Burial history diagrams across all depositional sequences in the candidate wells were also prepared to identify the depositional scenario and to estimate the time span of tectonic subsidence along the depositional sequences.The results of all available geological studies which recently have been carried out by Waha Oil Company in the area of study and adjacent areas have been reviewed, elaborated and integrated with the results of this study to assess the discussion and final conclusion. The final results of sedimentological study indicates that there is no major effect of diagenetic processes on the reservoir rocks during and after the deposition. As a consequence, C3-NC98 and C4-NC98 wells were drilled in an area of poor reservoir quality of Reworked Sandstone and Upper Nubian reservoirs due to the existence of thick sequences of clay and siltstone which were mostly deposited in levee and over bank sub-environments of likely combined braided and meandering river. Whereas, C1 and C2-NC98 oil wells were drilled in an area of good reservoir quality of Reworked Sandstone and Upper Nubian Sandstone reservoirs where the sand bars sub-environment are deposited as a thick sequence of clean sands carrying the genetic of good reservoir properties. Therefore, the reservoir rocks in this area have different properties due to different sub-environment of deposition. This new results will probably assess the prospect generation and evaluation for the future drilling activity in the area of study.The encountered volcanoclastic sediments in well C2-NC98 reveals that this sediment is likely transported by river from the area of volcanic eruption to the area of deposition rather than in situ eruption. This type of volcano is likely applied to cinder cone volcano type where the pyroclastic fragments are not cemented together and thus easy to erode. Therefore, the intercalation of volcanoclastic sediment in Upper Nubian Sandstone has no marked effect in the reservoir rocks.Burial history curves of wells C1-NC98, C2-NC98, C3-NC98 and C4NC98 indicate three major subsidence events took place during Early Cretaceous time (Early Aptian - Early Albian), Late Cretaceous time (Turonian - Maastrichitian) and the Palaeocene - Eocene subsidence. However, Plaeocene - Eocene subsidence shows the highest subsidence rate with comparison to the other two subsidence rates.
محمد عمار هامان (2015)

Abstract

The basaltic Intrusions of the Central Jabal Nafūsah Foothills which extend from NW Wādi Zāret to NE Wādi Ghān Dām are part of the latest stage of Gharyān Volcanic Province (GVP). These intrusions are classified on basis of their shape and mechanism of emplacement into four kinds of volcanic bodies. These are; sheets (dykes and a sill), dykes associated with volcaniclasts, volcanic cone and lava mounds. Generally, the dyke emplacements are restricted only to the area between Wādi Zāret to Abū Ghaylān, while the other forms extend from Rās al Mazūl Dome to Wādi Ghān Dam. The more differentiated rocks are restricted to the area between Rās al Mazūl Dome and Wādi Ghān. Farther west towards Wādi Zāret, ultramafic xenoliths and magnesium-number increase, suggesting closer proximity to the source. The rocks are essentially alkaline with within Intraplate signatures. They straddle the composition from picrites, basanites, alkali basalts through hawaiites, mugearite to benmoreites with a compositional gap between the last two types. Generally, the phenocrysts are represented by foresteritic olivine, Cadiopsidic pyroxene, magnesiotaramitic amphibole, plagioclase, K-feldspar and titanomagnetite. The chemical composition of the mafic minerals indicates that they are high pressure phenocryst phases. The most primitive picrites satisfied the criteria of primary mantle melts. The rocks are generally, enriched in LILE suggesting an enriched mantle source. The studied rocks were grouped into five groups based on incompatible trace element ratios; Group-A includes picrite, basanites and hawaiites, and Group-B includes picrite (Z-3), basanites , alkali basalts, and hawaiites, while Group-C is formed of hawaiites, Group-D is composed of mugearite and Group-E is made up of benmoreites. Picrites and basanites of these rock have high Mg-number (>0.64), high Cr and Ni contents and strong light rare earth element enrichment, but systematic depletion in Rb, K and Ba relative to trace elements of similar compatibility in anhydrous mantle. Alkali basalts and more differentiated magmatic rocks have lower Mg-number and lower abundances of Ni and Cr, and have undergone fractionation of mainly olivine, clinopyroxene, Fe–Ti oxide, amphibole and plagioclase. The variation in the concentrations of major, trace, rare earth elements, and incompatible element ratios in the rock samples demonstrate the heterogeneous character of their source region. Such heterogeneity can be interpreted by the involvement of a heterogeneous mantle reservoir to different degrees of partial melting. The REE data require residual spinel stability peridotite field in the source and constrain the melting process of Group-C and Group-D to 2% to 3.5% degrees of melting respectively, Group-A and Group-B both to 5% degree of partial melting while Group-E to 10% degree of partial melting of spinel lherzolite xenoliths of Al Ourban area. Mass balance modelling of the major suggests two possible FC scenarios; Derivation of basanites and hawaiites of group-A from G-3 picritic parental magma. Derivation of Group-D and Group-E was also possible from these basanites. Derivation of basanites of Group-B from Z-3 picrite parental magma and simultaneous derivation of G-4 and QJ-1 alkali basalts from Z-3 picrite parental magma. V Simple mass-balance calculations suggest that the melting assemblages of picrites and basanites consisted of forsteritic olivine, diopsidic clinopyroxene, Ti-magnetite. While the alkali basalts and more differentiated magmatic rocks, mass-balance calculations suggest that the melting assemblages consisted of sodic plagioclase, magnesiotaramitic amphibole, diopsidic pyroxene, Ti-magnetite, K-feldspar with sub amounts of apatite and sphene.
سمية عون (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)

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 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)