الفهرس 
Location of the study area
GEOLOGY OF NILE DELTAOnly 14 pages are availabe for public view
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Abstract
The present Nile delta area covers approximately 60,000 square km. Fields
in this area provide two-thirds of the gas production in Egypt, Around 58 Tcf
of gas reserves (Nini et al., 2010) have been discovered until now in the Nile
Delta province, it is therefore considered as the most prolific province for
gas production in Egypt.
The study area is the Baltim Development Lease: a large license located in
the present day Nile Delta, offshore Egypt. The concession covers about 430
Km2 of the central portion of Nile delta cone. In 1996 IEOC and partners BP
and EGPC acquired a total of 435 Km2 of 3D seismic survey for better
understanding the structural setting, the stratigraphy of the area and
characterize the reservoir types in order to increase the probability of success
in exploration.
Within The Nile Delta Basin gas is generated and accumulates at
stratigraphic levels ranging from the Oligocene to Pliocene-Pleistocene. The
main fields in the area are traditionally exploiting the Messinian (Abu Madi
formation). Recently several discoveries have been made in the PliocenePleistocene sections.
The Lower Pliocene has a different seismic response in comparison with
Upper Miocene and Middle to Upper Pliocene - Pleistocene sections
although pools from the whole of these sections are producing hydrocarbons.
The Lower Pliocene succession contains many turbidites channels, more
than 40 Km long and they are considered as a possible component of future
hydrocarbon exploration in this area. A detailed investigation of the lower
Pliocene reservoirs compared to the rest of the Neogene succession, through
classical seismic interpretation, seismic attributes analysis and AVO can
contribute to a better understanding of the reasons of the recognized different
response of the Lower Pliocene section from the other intervals and can give
support to possible exploration activities. The Middle to Upper Pliocene gas play is well established over the entire
offshore Nile Delta region; it consists of shelfal or turbidite channel and lobe
sands of Pliocene age sourced and sealed by interbedded shales generating
biogenic gas. Gas chimneys identified in the area are considered as an
important preferential way of hydrocarbon migration pre-Messinian kitchens.
Three wells (BN-1, BNE-1and ANDALEEB) have been used in this study,
encountering multi targets within the Neogene succession. Well BN-1
penetrated two seismic anomalies: one of them is gas bearing within the
Upper Miocene, while the other is water-bearing within the Lower Pliocene.
Well BNE-1 penetrated two gas anomalies one of them in Upper Miocene
and the other one in Lower Pliocene. Well ANDALEEB penetrated four gas
anomalies: three of them in Middle to Late Pliocene while the last one in
Lower Pliocene. The analysis of the identified anomalies on seismic was
performed following some subsequent steps: Well to seismic tie, seismic
interpretation, AVO analysis and Attribute analysis.
Well to seismic tie is used to detect the response of the anomalies in the
seismic. The synthetic seismograms show that the anomalies in Lower
Pliocene start with a trough (European polarity), while the anomalies in
Upper Miocene and Middle-Upper Pliocene start with a peak. After seismic
interpretation was done to follow the anomalies on the seismic it appeared
clear that, there are a different response on angle stacks is evident for Lower
Pliocene and Upper Miocene and Upper-Middle Pliocene ones. It is clear
that the latter can be seen easily on the far angle-stack while, the Lower
Pliocene ones can only be seen at near angle-stack. This is particularly
evident on amplitude maps extracted from angle stack volumes within small
time windows.
AVO plays a great role in the exploration, where it characterizing the fluid
content or the lithology of a possible reservoir and reducing exploration
drilling risk. By the integration of advanced seismic analysis and
sedimentlogical interpretation of the well data, that eventually resulted in the
productive sands in the succession within the Middle & Upper Pliocene and
Upper Miocene succession. There are characterized by class III AVO
response, where the gas sands have lower acoustic impedance than the
surrounded shales and they appear in amplitude extraction at the top peak in
the far angle-stack volume. Added, the Lower Pliocene appears in amplitude extraction at the top trough in near angle-stack volume and it appears by
class I AVO response, where the gas sands have high acoustic impedance
than the surrounded shale due to, the overlaid shale is proper fissile.
There is a relation between AVO and the depth due to different compaction
of sand bodies class III is characteristic of shallow reservoirs passing deeper
to class II and class I in deep and compacted pools.
The cross-plotting technique is the easiest method to compare and derive
relationships between different variables. rock physics cross-plotting is used
to analyze relation acoustic impedance with all reservoir interval and it
highlight that the reason for the unexpected AVO response within the
Neogene succession in the Nile Delta is the difference in the overlaid shale
not the reservoirs itself as we think before.
from this study the detection of gas chimney and associated structures as
preferential hydrocarbon migration pathways from the pre-Messinian kitchen
section to the Plio-Pleistocene reservoirs is testified by the numerous DHIs
within the upper Pliocene – Pleistocene reservoirs that are in contact with the
boundaries of the gas chimneys. In addition, geochemical analysis on gas
samples from targets drilled in the upper Pliocene – Pleistocene indicates the
presence of thermogenic gas clearly generated by pre-Messinian units.
In addition to direct hydrocarbons gas indicators, gas chimney presence has
been used in defining the most promising areas inside the exploratory blocks.
This approach has been mainly tested in the exploration of the PlioPleistocene interval. Areas interested by gas chimneys are obviously not
defective as regard the presence of an efficient hydrocarbon generating
system.
According to the present work we recommend to drill the Lower Pliocene
channels in the down thrown of the main fault due to the hydrocarbon was
migrated from the gas chimneys in the north to the south direction until the
main fault which it considered as the seal.
Enhance AVO Pseudogradient equation used before as a way to highlight
AVO class III anomalies only. But, according to the present work, we
approve new using for it to detect all AVO classes anomaly.
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Create and confirm a new equation (new model) which can be used to
differentiate between the gas and water anomalies for all AVO classes
anomalies.
According to the present work we recommend to use the new approaches
where the most common practical uses of the method can also be classified
in direct relation to these objectives:
• Quick search for new leads, highlighting their possible anomalous
behavior.
• Reduction of the geological risk, by providing additional elements for
ranking of identified prospects.
• Assessment of the distribution (2D / 3D) of reservoir fluids and
petrophysical parameters.
But the new approaches have limit use where they can be used in case the
AVO principles work with a good seismic quality.