الفهرس 
GEOLOGICAL SETTINGOnly 14 pages are availabe for public view
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Abstract
4D (time-lapse) seismic has become a powerful technology for oil companies to manage their reservoirs. The use of 4D technology is obviously a major investment for oil companies, and must be properly planned beforehand. time-lapse seismic has been proven to be very effective for monitoring not only gas production but also injection process. The process of gas production causes variations in reservoir parameters such as fluid types, fluid saturation and pressure and reservoir thickness and thus changes seismic properties of saturated reservoir rock. Therefore, it is crucial to the success of 4D seismic projects to make a feasibility study determining how we can properly plan 4D seismic surveys for a reservoir under consideration.The feasibility study can be summarized as follows:
Well Logging Analysis:-
The well logging analysis was carried on for sienna Reservoir in the selected two 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 water sample measurement. The volume of shale (Vsh) is calculated through GR as a single indicator and through neutron –density as a double indicator.but I used the GR calculation due to the gas effect in the neutron –density that make the shaly sand zone as a clean sand zone.
In this study the estimated rock porosity (Ф) was calculated by Density as a single indicator and neutron –density as a double indicator. but I used the density calculation due to the over estimation of the neutron –density. The determination of fluid saturations is carried out for shalysand zones in sienna reservoir by using Indonesian equation and the Archie equation didn’t applied because we didn’t have a clean sand zone in sienna reservoir.
This study evaluate The lithology and mineralogy of the sienna reservoir rock was studied using different Crossplots like NPHI – RHOB, PEF_RHOB, Th-K, PEF-K and PEF-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.
The vertical distribution of hydrocarbon occurrences is presented and explained through the litho-saturation Crossplots. These plots in the two wells show that the main production zone in sienna-1 well is sand-1 , thin bed, sand-2 zones and the main production zone in sienna-2 well is sand , thin bed zones .from litho-saturation crossplot of sienna-1 well the GWT at 2468.6 m. from litho-saturation crossplot of sienna-2 well the GDT.
AVO inversion:-
The work in the data gathering were completed in three axes; well data, seismic data and horizons. The data availability and the quality of the data is a major point in the study. The horizons were in good condition but well data and seismic data were needed to be conditioned. The necessary editing were performed to the well logs including the bad logs replacement, In sienna 1 well, the only log which has some bad log data is the density log, it has been corrected from depth (TVD) 2337m to 2373m using Gardner’s equation in sienna 2 well, the logs which have some bad log data is the density and shear velocity log, the density log has been corrected from depth(TVD) 2331m to 2355m using Gardner’s equation and the shear velocity has been corrected from depth(TVD) 2337m to 2356m using Castagna’s equation.
The pre-stack seismic data conditioning was done through three steps; first step is Frequency Filtering, second step is time misalignment correction and third step is amplitude balancing. some of the high frequency content were lost during the data conditioning but the AVO response become more realistic and close to the theoretical predictions after the conditioning. We used two different wavelet set; statistical wavelet set and deterministic wavelet set. The result show that the deterministic wavelets are better than the statistical wavelets for the seismic correlation in sienna-1 and the statistical wavelets are better than the deterministic wavelets for the seismic correlation in sienna-2 and but the inversion analysis is most better by using the statistical wavelet set.
The initial low frequency model was constructed using well log data and horizons.The three main rock physical properties for the Pre-stack inversion study are P-impedance, S-impedance and density. So these three logs from the two wells were interpolated by an inverse-distance algorithm so three intial models volumes were generated.and the log data is to be filtered by a high-cut filter in order to get the low-frequency model.
The final results from the simultaneous pre-stack inversion consisted of six volumes of P-velocity (Vp), S-Velocity (Vs), and density (ρ), P-impedance,s-impedance, Vp/vs ratio.
The rock physics modeling:-
The rock physics study used the well logs and the insitu parameter choosed for one point in the reservoir thickness that best represent the unconsolidated reservoir. The friable sand model and Gassmann fluid substitution was applied to show the effect of the increasing water saturation and the DROP in pore pressure in seismic properties .The products of AVO simultaneous inversion and well logging data can be modeled in the 2D models and then Appling the friable sand model and Gassmann fluid substitution to detect the change of the water saturation and pressure in seismic parameter in 2D model .