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Geisum Oil Field: Structure of Geisum Concession

The Geisum oil field is located in an area that was formed by faulting between the Arabian and African tectonic plates. The structure comprises northwest tilted fault block sandstone reservoirs that have been further dissected by cross-faulting. There are four depositional cycles represented by different sedimentary units from the Late Cretaceous to recent periods, overlying a fractured Precambrian basement. The primary reservoirs are the Matulla and Shagar sandstones, with the Matulla in the south having porosity up to 27% and the Shagar submarine fan deposits in the north reaching 100 feet thick with 19% average porosity.

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Ahmed Fouda
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114 views1 page

Geisum Oil Field: Structure of Geisum Concession

The Geisum oil field is located in an area that was formed by faulting between the Arabian and African tectonic plates. The structure comprises northwest tilted fault block sandstone reservoirs that have been further dissected by cross-faulting. There are four depositional cycles represented by different sedimentary units from the Late Cretaceous to recent periods, overlying a fractured Precambrian basement. The primary reservoirs are the Matulla and Shagar sandstones, with the Matulla in the south having porosity up to 27% and the Shagar submarine fan deposits in the north reaching 100 feet thick with 19% average porosity.

Uploaded by

Ahmed Fouda
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Geisum oil field

:Structure of Geisum Concession


The original structure comprises northwest tilted fault block sand horsts as a result of early rifting between
Arabian & African plates which then subjected to subsequent effect of the trascurrent fault of The Gulf of Aqaba
and dissected the existed fault block by NS-SW cross faults which developed an adjacent and tilted fault blocks
.plunging to the northwest
The average structure dip of the penetrated pre-Miocene & Miocene sedimentary units range from 35 o to 50o in
Nubia - Matulla formation which gradually decrease upward to about 8 o in Kareem formation. Generally, this
sedimentary unit are thinning up dip towards to the crestal area of the tilted block, either due to the non-
.deposition over the highs and/or as a result of the pre-Miocene unconformity

:Stratigraphy
The simplified stratigraphic section shown in the figure comprises a series of sediments from late Cretaceous to
Recent overlained the fractured Pre-Cambrian Basement
Which is mainly formed from granite, granodiorite & lucogranite. The preserved successive sedimentary units
.comprises four cycles of deposition
The first cycle was started by the deposition of relatively thin wedge of alluvial plain to marginal marine Nubia
sandstone. The Matulla formation was deposited under tidal shallow marine condition followed by the Brown
.limestone & the Suder Chalk
The second cycle of deposition took place as a resultof marine transgression, and deposited the open marine Esna
.& Thebes formations
The third cycle was started by the deposition of Nukhul formation under shallow marine with lagoon interval
conditions followed by marine Rudeis & kareem shale & limestone interrupted by a deposition of sandstone
.submarine fans which represent the North Geisum reservoir
The forth cycle is the Miocene-Recent evaporates which capped all the pre existing sediments

:Reservoir Data & Characteristics


:South Geisum Field -1
The fractured Basement & Matulla sandstone are producing oil from the south Geisum field. The fractured
Basement is characterized by the presence of different sets of fractures extending towards the NE-SW & the NW-
.SE directions. The estimated porosity ranges from 0 to 3%
The Matulla formation consist mainly from shale & siltstone interbedded by sandstone which are the primary
reservoir in the south. The sandstone are quartzose, fine to very fine grains, occasionally medium to coarse,
carbonaceous, micaceous & calcareous. The total sand thickness reach 200 ft on the flank decreases up dip as a
result of erosion the porosity ranges from 13 to 27% the average Sw is 26% and the permeability ranges from 400
.to 900 md, finally the water-oil contact is at -5400 ft

:North Geisum Field -2


Shagar sandstone of Kareem formation is the primary oil reservoir while Rahmi sandstone is the secondary
reservoir. The sandstone are quartzose, fine to very fine grains, very coarse to gravel at the channel base.
Thickness of Shagar submarine fans reaches 100 ft in the center of the field and decrease toward east & west. The
porosity ranges from 10 to 25% with 19% average porosity. the average Sw is 17% and the permeability ranges
fron 800 to 1400 md. The thickness of Rahmi sandstone ranges from thin layers on the upper part of the tilted
fault block to 170 ft down dip. The porosity ranges from 9 to 12%, the average Sw is 40% and the permeability
.ranges fron 10 to 300

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