الفهرس 
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Abstract
The primary goal of the study is to assess the structural style and main stratigraphic horizons in Nader field by the obtainable 2D seismic data and State- of- art analysis and interpretation of obtainable seismic and wells data. Moreover, to test the ability of improving seismic data as a result of reprocessing to enhance the quality of the seismic data i.e. enhancing signal/noise ratio. The study area is located in the north Western Desert, at the south western part of Shushan basin. It lies between latitudes 30° 34’ 40’’, 30° 32’ 40’’ N and longitudes 26° 57’ 36’’,26° 55’ 12’’ E. The available seismic lines for the current study are part of the South Khalda Ridge 3D seismic survey that had been acquired during late 2009 and early 2010 in 10 swaths. Navigation information in SPS (Shell Processing Support) format was used to apply the geometry information to the data. The total area of the surveyed region is 824.96 km2. The workflow begins through performing a correlation between wells to identify the stratigraphic rock unites that can be tied to the reflected horizons within the seismic sections. The wells are correlated and appropriate sand markers are chosen to define the various reservoirs. The correlation means the determination of the continuity and equivalence of lithologic units notably reservoir sands or marker sealing shales across the region of the subsurface. Different geologic processes deposit lithologic units with varying lateral continuity and developing a geologic concept of what is in the subsurface is important at this step. The initial step in seismic interpretation is to figure out how seismic reflections (in time) relate to well data (in depth). The process of creating synthetic seismogram using petrel software includes sonic calibration, synthetic generation, and wavelet generation. Through creating a synthetic seismogram, the interpreter ties time data (the seismic data) to depth data(the well data) by integrating over the velocity profile. Check-shot data are used to overcome the inherent uncertainties of the sonic log in tying the well to the seismic section to make the sonic calibration and a well (NDR-04) has been selected to generate synthetic seismogram. The well showed a good relationship between picked Two Way Travel time (TWT) and subsea depth (Z). In the current study, a synthetic seismogram for well NDR-04 was constructed using the sonic and density logs and the convolution of a broad band zero wavelet extracted from the seismic data. Generally, tying between this synthetic seismogram and the seismic data are satisfactory. After tying the seismic data with well top in NDR-04 to identify the important reflectors of horizons in the study area, more than one reflector should be picked above or under the target horizon to get an overview of the structure complexity in the selected region. Five horizons have been selected to interpret helped by applied many attribute techniques as cosine phase shift, an instantaneous frequency and variance (edge detection). The selected five horizons for interpretation are Apolonia, Khoman, Abu Roach-C, Upper Bahariya and Lower Bahariya formations and also Alamein Formation which has been recognized from (NDR-01)well in the Nader field. The depth contour maps of these formations are constructed to show their spatial distribution in Nader filed moreover the dissecting normal faults forming grabens,half grabens, and horsts. These structural features significantly control the trapping of oil and gas. The used wells are noticed to be drilled the local high structures (horsts) located in the center of the study area. Because seismic data is created in real time, and wells depends on seismic interpretations are in depth, the seismic interpreter is concerned with depth conversion. To correlate well data and do volume calculations, we may translate data from one domain to another, such as seismic data in time, by using depth conversion. The conversion of time to depth is accomplished using velocity information. A time interpretation’s depth conversion is straightforward and done anytime whenever data is available. The physical quantity that accelerates the passage of time is velocity. The P-wave velocity in the vertical direction is necessary for converting time to depth. It can be directly calculated in a well, indirectly from surface seismic data, or as a result of a mix of seismic and well data. Generally, in the study area, there are two main fault trends, the first fault trend is nearly oriented E-W direction and is attributed to the Paleozoic tectonic movement (Paleozoic rifting)in the north Western Desert. The second fault trend is oriented NE-SW which is related to the Jurassic rifting in north Western Desert. Relay ramps are prevalent in normal fault systems. They consist of a region of reoriented bedding that is between two normal faults with the same dip direction and overlap in map view. After the structural interpretation of the seismic data have been done, some processes are applied for line-1 and 12 to improve the interpretation of the final seismic section. Postprocesses have many objectives, the first is to improve the signal to noise ratio, while the second is to show the continuity of reflectors, fault detection then it may detect new horizons
and equalize the amplitudes of the final section. To better understand the quality of the current seismic data and to find out the optimum post-stack processing flow to increase its Signal to Noise Ratio, it is important to analyze the data in both time and frequency domains. The work flow was applied in the study area such as Ormsby, Butterworth bandpass filter, Time Variant filter, FX deconvolution, FK filter, Predictive and Spiking deconvolution. After applying many tests with changing the values of frequency content, the tests showed each filter parameters were applied to the whole section, it clarifies data enhancement in some parts and harsh in others, including the interested horizons. On the other hand, the time-variant filter (TVF) that is a variety of the Band Pass Filter is expected, when applied, to improve the whole seismic section. Then FK filter has been applied to remove the linear noises in the seismic section. It is one of quality control tool distinguish between the signal (wanted energy) and noise (unwanted energy). The FK spectrum can be used to limit both the temporal and spatial frequencies, any editing usually being done by marking part of the spectrum for removal and transforming back seismic data into the time domain. FK filtering can be also used at the end of the processing sequence to remove other sorts of noises such as multiples. Deconvolution is also important to remove coherent noise as energy coming from multiple arrivals. Deconvolution can be predictive or spiking, with the difference between the two being the length of the operator gap. A short, or no gap, gives maximal wavelet compression (hence the name spiking) while a large gap (32 ms or more) attempts to remove periodicity generated by short period multiples whose period is longer than the gap.