الفهرس 
GEOMORPHOLOGYOnly 14 pages are availabe for public view
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Abstract
The main purpose of the current study is to delineate the detailed structural
features affecting El-Obaiyed field using the available seismic reflection data. Also, to determine
the different Lower Safa reservoir parameters characterizing the pay-zone, utilizing well logging.
The first chapter of this study explains the geologic setting of El-Obaiyed field, which is one of
the good gas and condensate producing fields in e Matruh basin that was discovered in 1989 by El-
Obaiyed 1-1 well.
Matruh basin was opened in the Early Mesozoic (Triassic) time, as a NNE-SSW oriented and passive
continental rift. Tectonic subsidence during the Triassic, Jurassic and Early Cretaceous led to the
deposition of large northeastward thickening wedges of syn-rift sediments. Erosion of pre-rift
(Paleozoic) rocks is bounding the Matruh basin at the south and west (Faghur platform).
El-Obaiyed field lies on the western platform margin of the Matruh basin, where the early rift
detritus, that was deposited mainly in the low parts of the rift flexural
area represents the main reservoir. The Lower Safa is the main reservoir in El-obaiyed area and
bounded by two unconformity surfaces. The Lower Safa Member thickness varies across El-Obaiyed
area, but generally increases toward the northeastern direction.
The main problems in EL-Obaiyed area are the fast lithologicvariations in the reservoir quality and
thickness, in addition to the structural complexity of the area. The available geophysical data for
the current study are:
8 composite logs for 8 wells and a location map, provided by the Egyptian General Petroleum
Corporation (EGPC) and Badr Petroleum Company (BAPETCO) of Egypt, including resistivity, gamma-ray,
density, neutron, sonic, caliper and composite logs.
30 seismic profiles (2D seismic reflection data) and some velocity data,
that cover most of the study area. The seismic data were contributed by the Egyptian General
Petroleum Corporation (EGPC) and Badr Petroleum Company of Egypt.
The second chapter shows how the seismic data were acquired and processed to be ready for the
interpretation.
The principal objective of the 3D seismic survey was to acquire high quality and well defined
seismic data safely and efficiently. The survey is covered 730 square kilometers, which was
comprised of 124 receiver lines running in a north / south direction, and 119 source lines running
in an east / west direction. The energy source was vibroseis.
The seismic data were recorded via telemetry is recording system, utilizing a symmetrical receiver
patch of 2,304 receiver channels on 12 receiver lines, four vibrators were used for shooting the
shot points with a frequency range of 6-60Hz for a nominal average of 192 fold subsurface coverage.
The 3D seismic data were acquired and processed by ARDISEIS CGG. The data were processed through
computer softwars to convert the field recordings from the shot domain into meaningful seismic
sections. The main target of El-Obaiyed 3D seismic data processing is a structural objective at
deep target (TWT of about 1.7–2.5 sec) of clear fault definitions, because of the high level of
noises and clear image for the small scale structural features of El Khatatba Formation.
The third chapter reveals the interpretation results of 30 seismic lines covering the study area.
By studying El- Obaiyed field through the available seismic reflection data and mapping the
different levels: Top Khatatba Formation for the Jurassic, top Alamein Formation for the Early
Cretaceous and top Abu Roash Formation for the Late Cretaceous; it is clear that, El-Obaiyed field
is characterized by gentle NE dip, a small thickness of syn-rift sediments, small rate of tectonic
subsidence and affected by three main structural trends: The First structural trend is the NNE-SSW
oriented faults, that dissected only the deeper stratigraphic Jurassic and Paleozoic units. It
divides El- Obaiyed field into three NNE-SSW oriented rectangular blocks at the top Khatatba level.
These fault blocks named as OBA NW block, Obaiyed block and Sharaif block. The second structural
trend is the NW-SE oriented faults, which dissected the Upper Cretaceous rocks and don’t cut throw
the deeper section, and died out within Alam El- Buieb Formation, which act as a ductile section
can absorb the fault energy and doesn’t
allow the structures to propagate downwards. The third structural trend is the NNE-
SSW oriented anticlines, which affect the Upper Cretaceous section and lie exactly above the
NNE-SSW oriented faults, that affect the deeper stratigraphic units. These folds have their largest
vertical closure in the Abu Roash Formation. These asymmetrical anticlines represent the fault
propagation folds formed during the phase of positive structural inversion.
The seismic data don’t help more for the stratigraphic seismic interpretation, except it shows very
clear thickening of the Jurassic section toward the NNE direction and the thinning toward the SSW
direction, which means that the southwestern area was of higher Paleozoic topography than the
northeastern area. Gentle NE dipping of the Lower Safa gives indication that, the basin extends in
the NE direction.
The fourth chapter shows the petrophysical analysis results of 8 wells in El- Obaiyed field (OBA
3-1 st, OBA NW-2, OBA D1, OBA D3, OBAD13, OBA S-1, JB
16-3 st and JB 18-1 st). The well log data are including resistivity, gamma-ray, density, neutron,
sonic, caliper and composite logs. The main petrophysical parameters needed to evaluate a reservoir
are its growth thickness, net sand thickness, porosity and hydrocarbon saturation. The gross
thickness of the reservoir ranges from 0 m to more than 150m, the porosity ranges 5% to 12%,
hydrocarbon saturation in the gas bearing sand also range between 60 to 85% and Permeability is in
the range of 0.01 to 100 md and characterized by high lateral and vertical heterogeneity.
Mapping of these parameters shows the thickness and quality variation of the reservoir, in which
the NW and SW parts of the field were act as paleo highs during the deposition times of the Lower
Safa, so the wells which drilled in these parts didn’t encountered the reservoir and the drilled
Paleozoic rocks below Kabrit Member directly. The reservoir thickness increases toward the NE
direction. The reservoir facies is also deteriorated toward the eastern direction and the Lower
Safa became more shaley.
The last chapter explains the petroleum system and the hydrocarbon prospectivity of El-Obaiyed
field, which have been identified by the integration between the seismic
data and the well log data. The good matching and integration between the seismic data
and well log data tells a good story about the petroleum system of El-Obaiyed field.
The source rock quality in El-Obaiyed and Matruh basins is represented in Khatatba coals and shales
with TOC of 20 to 55 wt%. The liquids (condensates) obtained from the Lower Safa reservoirs within
El-Obaiyed field show a consistent source rock and relatively small variations in the maturity. In
El-Obaiyed field, the Khatatba shale/coals are mainly of type II/III Kerogen.
Kabrit shale and limestone represent a good seal of the Lower Safa reservoir. It covers the
reservoir all over the field. Lower Safa sands represent the main reservoir rocks in El-Obaiyed
field. It is composed from very fine sand size, with the presence of clay minerals, mainly
kaolinite and illite.
Generation of hydrocarbons form the Khatatba source is believed to be around 100 million years
(Aptian time). The timing of peak hydrocarbon expulsion is believed to be in the Oligocene time.
The main migration paths entered El- obaiyed field are from the NE direction, where the Khatatba
source rock is more shaley and deep.
El-Obaiyed is the largest Jurassic gas/condensate field in the northern Western Desert of Egypt. It
represents a combination trap on the western flank of the Matruh basin; a NNE trending
Jurassic-Early Cretaceous rift, that was inverted in the Late Cretaceous - Early Tertiary. The
field lies within the up-dip side of a large easterly- tilted half graben. It produces from the
Bathonian sandstone unconformably overlying the pre-rift Paleozoic sequences.
Seismic and well log data are widely used in petroleum exploration to map the subsurface
reservoirs. The two data sources are complementary: seismic profiles provide an almost continuous
lateral view of the subsurface, whereas well logs yield fine vertical resolution of the geology at
the borehole. Seismic profiles can resolve, with relatively high precision, the structural and
stratigraphic changes from the arrival times and amplitudes of the reflection events. The
integration of well log and seismic data would provide a high degree of reliability in mapping the
subsurface structural and stratigraphic plays.
For Lower Safa thickness prediction, there is a promotional relation between the
isochrones TWT of the top khatatba and intra Paleozoic seismic marker (seismic data) with the Lower
Safa reservoir growth thickness (well log data). By the end, in conclusion, we can use the seismic
data to detect the presence of reservoir (the loop continuity) and the expected depth and
thickness. Well log data can be used to define the reservoir facies and its parameters, with their
role in the prediction of the stratigraphic sequence
For Lower Safa thickness prediction, there is a promotional relation between the
isochrones TWT of the top khatatba and intra Paleozoic seismic marker (seismic data) with the Lower
Safa reservoir growth thickness (well log data). By the end, in conclusion, we can use the seismic
data to detect the presence of reservoir (the loop continuity) and the expected depth and
thickness. Well log data can be used to define the reservoir facies and its parameters, with their
role in the prediction of the stratigraphic sequence