ملخص
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.