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The study area lies in what is known as ’’ The Great Sand Sea’’ and the terrain is covered in its majority with thick sand dunes ( the largest of the dune-covered areas in Egypt) varying in height and running in NNW- SSE direction.
The regional structural development of the region throughout the geological history was mostly controlled by the Paleozoic tectonic cycles and later by the Jurassic events associated with the opening of the Neo-Tethys Ocean.
South Siwa area is a relatively small intracratonic depression developed farther south in the southern parts of Western Desert. It was developed during the Paleozoic time and was probably part of a larger Paleozoic basin combining the Kufra, Dakhla and Foram basins.
The present structure framework of the basin was further developed during the Jurassic tectonics related to the opening of the Tethyan Ocean. It accommodates more than 4500 meters of Paleozoic, Mesozoic and Tertiary strata.
The main objective of this study is to map structural configuration affecting on the South Siwa area depending on seismic, dipmeter, and gravity data. 2D seismic interpretation was carried out on the study area to build a regional geological view about it. But as a result of the surface topography, most of the seismic lines were shot in NNW-SSE direction parallel to the longitudinal sand dunes with large line space. In order to overcome this problem, the available geological and geophysical data will be analyzed to give integrated and reliable structural picture for the study area.
Other objectives are: firstly; review the exploration history and activity in the study area to outline the regional geological setup of the area.
Secondly; understand the tectonic and structural trends of the area and delineate the subsurface target horizons in the study area. Thirdly; evaluate the hydrocarbon potentialities of the reservoirs in the study area.
Chapter one discusses the location of the study area, aim and objective of the study, the available data, methodology and technique used, and the exploration history and activities done in the study area. Chapter two deals with four main items, firstly; the subsurface stratigraphy of the Southern Western Desert, with special reference to the area under investigation, secondly; the structure pattern result of the tectonism effect on the study area, thirdly; the tectonism effect on the study area and lastly; the arrangement of various stratigraphic, structural and tectonic framework in a compiled form to reflect the geologic history of the study area.
Chapter three discusses seismic data interpretation of the available seismic data in the study area. A set of time and structural contour maps generated from the seismic data on top Upper Cretaceous (Cenomanian), Jurassic, Upper Carboniferous, Lower Carboniferous, Upper Devonian, Lower Devonian, and Cambro-Ordovician ages, were constructed using Petrel 2009 Seismic Interpretation Software and were useful in reflecting the prevalence of structural tectonic trends. These trends of local structures are believed to be produced as a result of comparable systems of regional tectonic deformations affecting the surrounding regions. The trends of the faults are: NNW-SSE, NW-SE, E-W, WNW-ESE, NE-SW, and ENE-WSW directions. But as a result of the surface topography, most of the seismic lines were shot in NNW-SSE direction parallel to the longitudinal sand dunes. So, the obtained structural maps show poor image about structures in the subsurface.
Structural image was achieved through analysis of dipmeter data in chapter four to give information about faults and unconformities in the study area. Faults have trends in NW-SE, and NE-SW direction were detected and matched with faults from structure contour maps from the seismic method, unconformities between Upper Cretaceous (Cenomanian) and Jurassic ages, and between Jurassic and Upper Carboniferous ages were detected too. But due to a limited number of wells (only one well) in the study area a complete structure view was not available. Therefore another source of geophysical information is required; stripped-on gravity maps that were derived from the Bouguer anomaly gravity map of the South Siwa area were constructed for Cretaceous, Jurassic, Upper Carboniferous, and Lower Devonian rocks.
By combing information obtained from structural contour maps derived from seismic interpretation, structures obtained from dipmeter analysis and matching them with stripped-on gravity maps in chapter five, the structural configuration through the South Siwa area could be mapped. This integrated interpretation reveals the trends of subsurface structural features which can be described from the oldest to recent as follows:
1- The NNW-SSE Trend: The major set of the NNW-SSE trending normal faults affect the study area, are believed to be produced as a result of one of the regional tectonic deformations in the Early Paleozoic (Caledonian orogeny which resulted in Calanshiyu arch).
2- The NE-SW and E-W Trend: another event mainly of Carboniferous-Permian age that resulted in NE-SW (due to Dhalma-Bahariya arch which is a Hercynian structural element trending in a NE-SW direction) and E-W (Varsican- Tethyan trend) trending normal faults.
3- The ENE to NE Trend: due to tectonic event mainly of Jurassic age related to the opening of the Tethyan Ocean produce ENE to NE trending normal fault.
A suite of well logs including the gamma ray, spontaneous potential, resistivity logs, density logs in the study area were evaluated to obtain the various petrophysical parameters.
Petrophysical reservoir characteristics were evaluated for Upper Cretaceous, Jurassic, Carboniferous, and Lower Devonian rock units encountered in three wells in the study area and its vicinity by applying Techlog software. This analysis recorded some sand zones within the studied sections in Foram-1 well of different thicknesses (from 125 to 579 ft.) having good reservoir properties (Vsh from 1% to 24%, Φt from 25% to 34% , Φe from 24% to 32% , Swt from 90% to 97% , Swe from 80% to 90%, and Sh from 3% to 10%) , while in Ammonite-1 well, the thickness of sand zones varies from 150 ft. to 600 ft. , and the reservoir properties are :Vsh from 4% to 12%, Φt from 13% to 29% , Φe from 12% to 28% , Swt from 80% to 98% , Swe from 80% to 98%, and Sh from 2% to 20% , and in Desouky-1 well, the thickness of sand zones varies from 775 to 1125 ft. , and the reservoir properties are :Vsh from 11% to 16%, Φt from 23% to 26% , Φe from 15% to 20% , Swt from 85% to 96% , Swe from 80% to 90%, and Sh from 4% to 15%.
This evaluation is anticipated to be guidelines for any future exploration in this area