الفهرس 
CHAPTER (1): INTRODUCTION AND PREVIOUS WORKOnly 14 pages are availabe for public view
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Abstract
Zeit Bay Oil field is located in the southwest offshore margin of the Gulf of Suez, in a shallow water depth, just east of Ras El Bahar Peninsula. The field is located 65 km. north of Hurghada, 85 km south of Ras Gharib.
This thesis deals with the coordination between the formation evaluation of the well logs and the subsurface geology of the Zeit Bay oil field in the Gulf of Suez to evaluate the characteristics of the Kareem/Rudeis Fm. carbonates reservoir rocks penetrated in this area.
The subsurface geological investigations were accomplished by a study of the lithostratigraphy of the field area with special reference to the lithofacies analysis and the environmental depositional conditions of Kareem and Rudeis Formations as they show complex facies and lithologic relationships. Besides, the outlining of the regional structural deformation and the tectonic implications operated in the study area was also attempted
Well log data from wells drilled in the Zeit Bay field were interpreted and integrated with other subsurface information to evaluate the reservoircharacteristics in the study area for more exploration and development activities. For this purpose several types of maps and illustrations were conducted.
The constructed isochore maps show that the thickness of the Basement Wash increases towards the northwestern and the northeastern sectors of the field area. The thickness distribution of the Pre-Miocene Sandstone is strongly affected by the structural relief of the Basement Complex upon which it was deposited. Its thickness increases towards the western and the north-central parts of the field area. The Basal Miocene rocks are represented in the study area by reduced thickness which may be due to the little structural relief that was during the deposition of the earliest Miocene sediments.
More emphasis was made on Kareem and Rudeis Formations as they show a complex facies and lithologic relationships.
The isochore map of Kareem Formation shows two basinal areas occupying the western and eastern sides of the field area, separated by a structurally high ridge trending NW-SE . The isolith maps and the panel diagram whichconstructed for Kareem and Rudeis Formations denote the following conclusions:(1) The Kareem and Rudeis Formations , which occur below Belayim evaporites, contain two very different facies The first one is thick shoal-water carbonates that mainly represented by Rudeis and Kareem dolomite, while Kareem limestone was resulted from deeper water and more open marine environment developed along the western margin of the fault block near the end of kareem deposition . Carbonate deposition ended with an abrupt rise in sea level and accumulation of the Kareem shale (second facies), overlying the carbonate in most of the field mainly between platforms. The third facies encountered in the Kareem and Rudeis Formations is the Kareem sand which is only represented in the northern part of the study area overlying the Rudeis dolomite and equivalent to the Kareem carbonate.(2) The Kareem / Rudeis interval is a slightly upward-shoaling sequence, with the exception of the capping limestone and shale facies . Variations in depositional conditions were minor and indicate only subtle difference in water depth or circulation.
The sequence of Belayim Formation is generally attenuated in the central parts of the field area, and it is well developed on the flanks especially the northeast and the southwest ones. Also, the thickness of Sidri and Hammam Faraun Members increases towards the flanks of the field area. The thickness of South Gharib Formation is variable over the field area and it generally increases towards the central parts around QQ-89-1 well.
The structure contour maps show an anticlinal structure occupying the whole area of study and its crest is present in the central parts around ZB-C6 well. This anticline is intersected by a huge horst structure bounding the field area, and a set of major and minor faults. These faults can be grouped in three trends: NW- SE, WNW-ESE and N-S; and they separated the study area into a number ofmajor and minor fault blocks. The major fault blocks include two horst, two step and two graben blocks. This structural configuration is inferred from the basement relief map and also clearly shown, with slight differences, on the other structure contour maps constructed on the tops of Pre-Miocene, Kareem and Belayim Formations.The paleostructural cross sections reflect the structural history of the Zeit Bay field area which can be summarized as follows:
(1) Steady subsidence during Pre-Miocene Sandstone to Eocene deposition.
(2) Fault block uplifting, tilting and erosion at the end of Eocene. The tilting probably took place along the eastern boundary fault. The resultant was deep enough to strip the sedimentary cover and expose the basement in the east. This erosion was leaving an erosional wedge of Pre-Miocene Sandstone in the west and with a girdle of younger sediments.
(3) Early Miocene transgression, results in deposition of Basal Miocene sediments. Variable thicknesses indicate filling-in of basement topography. The deposition continued forming the Kareem/Rudeis and Belayim sequences, with syn-depositional fault movements (growth faults).Comprehensive formation evaluation procedure was carried out, by means of computer programme, for Kareem/Rudeis carbonate, that encountered in the studied wells.
The determination of the shale content (Vsh) is achieved through five shale indicators: gamma-ray, neutron, neutron-density, neutron-resistivity and (ΦN) crossplot. The minimum shale content given by these indicators, is likely to be very close to the actual value of (Vsh). In this study, the Corrected Gamma Ray (CGR) of the Natural Gamma Ray Tool (NGT) is the most usable shale indicator.
The determination of the corrected effective porosity (ΦE) is executed using the combination of the density and neutron logs; after applying the various corrections. The determinations and discriminations of the fluid contents as water and hydrocarbon (gas and oil) saturations are also carried out for each zone.The concluded petrophysical parameters for the various wells are presented in the form of litho-saturation crossplots. The average of these parameters is achieved by using the weighted average equations. Average values are used for the construction of a set of iso-parametric maps for each reservoir zone encountered in the study area.The vertical and horizontal distribution of hydrocarbon occurrences, as has been exhibited from the litho-saturation crossplots of the evaluated wells and the iso-parametric maps of the study area show some general outlines.
The Lower- Middle Miocene (Upper Aquitanian-Serravallian) Kareem and Rudeis formations of the Gulf of Suez are composed of mixed siliciclastic/carbonate rocks.
The Kareem/Kareem/Rudeis Carbonates is described as heterogeneous reservoir and petrophysically divided into three Zones as:
1- The upper is the Limestone zone with low petrophysical parameters so that it is low in production rates.
2- The Middle is the Low Gamma Ray Dolomite zone with moderate petrophysical parameters and so it is characterized by moderate production rates.
3- The lower is the High Gamma Ray Dolomite zone with high petrophysical parameters and high production rates.The Kareem/Rudeis Carbonate Reservoir are volumetrically the largest reservoir unit in the field, containing approximately 50% of the total reserves. Generally, Kareem/Rudeis carbonate is a good to very good porosity level. The water saturation increases from 5% to 32% towards the northeast of the study area, while the hydrocarbon saturation increases from 68% to 95% towards the high central parts.Petrophysical analysis and subsurface studies concluded that there is a clear relationship between the structures (Faults) and petrophysical properties such as porosity, permeability, clay contents and hydrocarbon saturation values. The faults position and around areas, have high porosity and permeability values due to the effect of the faulting in carbonate reservoir rocks that increased the fracturing, vuggs and caves. This improved the hydrocarbon productivity and enhanced the oil recovery from such carbonate reservoirs rocks.The Kareem/Rudeis Carbonate have been subjected to microfacies
investigation using the polarizing microscope. The microscopic examination of
this formation in the study area greatly helps in interpreting their depositional
environment and also described the paleoecologic conditions, as well as the
diagenetic processes.The petrographic investigation highlighted the main mineral components, textural aspects, diagenetic features and pore types geometry of the studied carbonate samples. Eight microfacies association were identified in the carbonate of Kareem/Rudeis formation in Zeit Bay oil field: dolosparite, anhydritic dolomicrite, sandy dolosparite, coralline microsparite, algal microsparite, sandy algal dolostone, sandy algal foraminiferal dolomicrite and anhydritic micrite microfacies association. The post-depositional changes are observed in the studied rock units include (in a paragenetic sequence): cementation, recrystallization, dolomitization, pressure solution, dedolomitization, dissolution and fillings.Petrographical studies of the Kareem and Rudeis formations revealed the presence of different types of secondary porosity which include: intra-intercrystalline, vuggy, fractures and channel porosity. Dissolution dolomitization and dedolomitization were improved the reservoir quality and generated secondary porosity such micro-inter-crystalline and vuggular porosity, while cementation had most effect on decline the porosity and permeability in the Kareem/ Rudeis carbonate reservoir.
Dissolution, dolomitization and dedolomitization are the main diagenetic feature which create secondary porosity such moldic and vuggular, and intra-intercrystalline. The Kareem/Rudeis carbonate reservoir is graded from good to very good quality depending on the degree of the post–sedimentation diagenetic processes.For the reservoir modelling and characterization, the higher order Sedimentary cycles are considered based on the aforementioned Cyclolog patterns (truncation and flooding events) that could be supported by its fossil content and characteristic lithotypes. The evolutionary patterns (aggrading, prograding and retrograding), these trends will be supported by frequency and abundances of the biotaxa in addition to the main lithotypes to support the possible systems tracts. The cyclicity patterns of the study wells could support the distinction of six 3rd order cycles that include 32 higher order cycles (Fig. 6.34). The age dating of the Syn-Rift cycles is controlled by high resolution biostratigraphic analyses (Chapter 2 of the present study)