الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 189 |  |  |
| | | from | 189 | | |
Abstract
The present work is devoted to the study of the general geological setting and structure setup of Sequoia reservoir within EL Wastani Formation in the north western margin of the Nile
Delta. Also, a pretrophysical analysis was made for the reservoir rocks through calculation of petrophysical parameters(porosity, shale volume , permeability , water saturation and hydrocarbon saturation) in each of studied nine wells to develop lithosaturation Crossplots and the lithologic identification Crossplots besides the lateral variation of the lithology and the different saturation distributions in the area . A Comparison between Dual water model and Indonesian Model for water saturation calculation and also between conventional tools results and advanced tools results (CMR) to select the most suitable model for the Sequoia reservoir. Study the reservoir connectivity and water levels through pressure-depth plots was conducted as well.
The study can be summarized as follows:-
Geological Setting:-
Nine wells were selected in the study area from Sequoia field west delta deep marine concession, 3 exploratory and 6 development wells. The subsurface sequence penetrated by these nine wells is mainly consisting of a sedimentary section ranging in age from Pliocene to Recent. . The Sequoia reservoir was encountered by these wells in the Pliocene sandstones of the El Wastani Formation and subjected to formation evaluation process and complete subsurface evaluation. The Wastani Formation can be interpreted in terms of a Pliocene deep-water canyon fill deposited on a delta-front slope.
It lies along strike from a number of analogous canyon systems which constitute the reservoirs of the WDDM succession.
The major structures within the Concession area are the SW/NE trending Rosetta Fault and the ENE-WSW trending Nile Delta offshore anticline.
Well Logging Analysis:-
The well logging analysis was carried on for Sequoia Reservoir in the selected nine wells in the study area. The procedure including the determination of the fluid resistivities (Rm, Rmf and Rw) at the studied formation temperatures. The water resistivity (Rw) was determined by two techniques: water sample measurement and resistivity in clean water-bearing zone.
On the other hand, the uninvaded zone resistivities (Rt) were calculated from the available resistivity logs, -Laterologs; taking into account the effect of bore hole, adjacent beds and invaded zones through a computer petrophysics software (Interactive Petrophysics ) developed by Schlumberger.
The volume of shale (Vsh) is calculated through GR and resistivity methods as a single indicator and through neutron –
density as a double indicator.
In this study the corrected rock porosity (Ф) was calculated by - conventional tools from: Sonic, Density, Neutron logs - and advanced tools from CMR tool.
The determination of fluid saturations is carried out for both clean and shaly zones. In the clean zones Archie equation was applied ,but for shaly zones Dual water model and Indonesian model were applied, and the results were compared with the water saturation calculated from CMR tool. It is concluded that the closest results to CMR results are those for Dual Water model.
The narrow difference between SWE calculated from CMR and SW calculated from conventional tools is due to the fact that the conventional tools are fluid and lithology dependent while CMR
is only fluid dependent especially resistivity tools which are affected by fluids and matrix which play an important role in Dual water saturation calculation as they have approximately the same trends of increase or decrease.
Permeability Determination The NMR data is used extensively to compute ermeability This is because there is a direct correlation between permeability and the following Parameters:
-Surface area/Pore volume ratio(S/V) -Pore throat diameter and hence pore size
-Porosity:
So that in this study Timur-Coates model is used to calculate permeability as it is the best method for gas reservoirs .
Lithological and Mineralogical Evaluation This study evaluate The lithology and mineralogy of the Sequoia reservoir rock was studied using different Crossplots like density – neutron , Th-K, PE-K and PE-Th/K Crossplot . These plots show that the reservoir rock is mainly composed of sandstone matrix with shale interbeds. In mineralogy the rock mainly composed of mixed layer clay, montmorillonite, illite and moderate percentage of mica and glauconite.
Hydrocarbon Potentialities:-
The vertical and horizontal distributions of hydrocarbon occurrences, have been exhibited from the litho-saturation Crossplots of the nine evaluated wells and through the isoparametric maps of the study area, which show some general outlines.
A. Vertical Distribution of the Petrophysical Parameters:-
The vertical distribution of hydrocarbon occurrences is presented
and explained through the litho-saturation Crossplots. These plots in the nine wells show that the main lithology of the Wastani Formation is claystone with streaks of sandstone and siltstone, while Sequoia reservoir is mainly sandstone with shale interbeds.
The average calculated porosity by conventional tools is ranges from 18% to 32 % while for CMR is ranging from 18% to 31 %.
The average calculated water saturation by conventional tools is ranges from 38% to 68 % while for CMR is ranging from 39% to 77 %.
B. Horizontal Distribution of the Petrophysical Parameters:-
The horizontal distribution of hydrocarbon occurrences was studied and explained through a number of porosity , permeability and saturation maps of the Sequoia reservoir which calculated by CMR tool and conventional tools . Maps show a decrease in effective porosity and permeability in the middle part around Sequoia D2 and Rosetta 10 wells and increases as going to north toward Sequoia D6 well and in the southern part at Sequoia D1 location , For the water saturation there is increase in the middle part around Sequoia D2 and Rosetta 10 wells and decrease as going to north toward Sequoia D5 well and in the southern part at Sequoia D1 well location .
Reservoir Connectivity :
MDT pressure data were taken for 7 wells to several compartments in the Sequoia field Sequoia . The Pressure data analysis shows that the Sequoia-D6 area has already been modelled as a separate compartment but the rest of the field has been treated as one interconnected reservoir but there is a slight pressure difference between the south and north of the field.
The free water level for Sapphire 1, and Sequoia D4 is located at 1532 TVDss.
Rosetta 10 and Sequoia D1 wells in the southern part have the same pressure trend which is different from the north part and the free water level is located at 1512 TVDss.
There is also another trend appearing in Sequoia D4 parallel to the main pressure depth trend which indicates a presence of thin beds in both wells .