Q1: Discuss the following: (15 Marks)
1) Tectonic evolution and structural setting of the Arabian
Plate.
2) Sedimentary basins of the Middle East.
3) The concept of Petroleum system.
Q2: Explain reasons?
(8 Marks)
1) Differences between Paleozoic oils derived from
clastic Qusaiba Member source beds and
those
generated from younger, carbonate source beds of Jurassic and Cretaceous age.
2) Arab D reservoir
accounts for most of the Jurassic oil production in the Arabian-Persian
Gulf region, forming many super-giant and
giant fields.
Q3: Write short notes:
(17 Marks)
1) Reservoirs of the Central Arabia Qusaiba-Paleozoic Total Petroleum System of
the
greater Ghawar area.
2)
Traps of the Arabian
Sub-Basin Tuwaiq/Hanifa-Arab
Jurassic
Total Petroleum System
3)
The D3B zone.
4)
Seal Rocks of the Paleozoic and Jurassic sections in the greater Ghawar area.
Model Answers
Q1:
1)
Tectonic Evolution and Structural Setting of the Arabiian Plate
The tectonic evolution of the Arabian Plate can be summarized
in five phases as follows:
(1) The first phase is a Precambrian compression
phase, when island-arc and micro-continent terranes accreted and assembled to
form the Arabian Plate from about 715 to 610 Ma. Many of the structural
elements that formed during this period controlled later sedimentation,
structural development, and petroleum accumulation.
(2) The second phase involved late Precambrian to
Late Devonian extension and subsidence from 610 to 364 Ma. Infra-Cambrian
sedimentation was largely controlled by the development of intracratonic rift
basins associated with the Najd Fault System, with evaporites and carbonates
accumulating in equatorial latitudes. In the Silurian, a major source-rock
sequence was deposited that was related to high-latitude sedimentation,
including glacial sequences in the late Ordovician.
(3) The third phase occurred during the Late
Devonian to mid-Permian (364 to 255 Ma) and encompasses the mid-Carboniferous
Hercynian Orogeny. Late Carboniferous and Early Permian glaciation followed the
orogeny, and the glaciation ended before the opening of the Neo-Tethys Ocean,
which started the fourth tectonic phase.
(4) The fourth phase (255 to 92 Ma) commenced with
rifting and associated passive margin settings. The upper Paleozoic and Lower
Mesozoic (Triassic and Jurassic) rocks are largely cyclic carbonates and
evaporites, whereas the lower Cretaceous strata are dominantly open marine and
a mixture of clastics and carbonates that were deposited along the Neo-Tethys
Shelf.
(5) In the fifth phase, the Zagros Orogeny
extended from late Cretaceous time (92 Ma) to the present-day, and was largely
compressional. This stage resulted in the closing of the Neo-Tethys Ocean,
and the development of a foredeep associated with its closure. Ophiolite obduction in Oman, followed by the uplift of the Oman Mountains,
the collision of the Arabian Plate with Asian continent to form the Zagros
Mountains, and finally the rifting of the Red Sea and Gulf
of Aden in Tertiary time, all occurred during this final phase.
2) Sedimentary basins of the Middle
East.
The Middle
East is divided into three major sedimentary basins:
(1)
The
Greater Arabian Basin, Saudi Arabia;
(2)
The
Zagros Basin,
Iran;
and
(3)
The
Oman Basin,
Oman.
Each basin is further divided into
sub-basins, and each of these has its own style and time of origin reflected by
differences in thickness and lithology.
- Tabuk Sub-basin, Saudi Arabia: Lies in the north-western Saudi Arabia.
- Widyan Sub-basin, Saudi Arabia: Lies on the eastern
side of the Ha’il-Rutbah Arch in northern Saudi Arabia.
- Sirhan Sub-basin, Jordan: Located in the central Jordan and
trends NW-SE.
- Rub
al Khali and Ras al Khaimah sub-basins: These sub-basins trend and
plunge to the northeast and located in Saudi Arabia and U.A.E.
- Palmyra and Sinjar
Sub-basins, Syria
– Iraq: Located
in Syria and Iraq.
- The
Mesopotamian Sub-basin, Iraq:
Located in Iraq
(also known as the central Iraq
Sub-basin)
- Red
Sea and Gulf of Aden Sub-basins, Saudi Arabia – Yemen:
Located in Saudi Arabia
and Yemen.
3) Petroleum system
A petroleum system is a natural
system that contains active source rock that is:
- Generating
and expelling petroleum at the critical moment of maximum burial depth (at
which temperature can activate the conversion of organic matter in the
source rock into oil and gas).
- This
includes all the geological elements of source rocks, reservoir rocks,
seal rocks and overburden rocks, the process of trap formation and the
generation, migration and accumulation of petroleum.
Q2: Explain reasons?
1) Differences between Paleozoic oils derived from
clastic Qusaiba Member source beds and those generated from younger, carbonate
source beds of Jurassic and Cretaceous age.
- The Paleozoic-sourced oils have lighter API gravities and lower
sulfur and trace-metal contents. API gravities of Paleozoic oil range
from 40° to 53°, whereas Mesozoic oils are commonly in the range of
20°-40°.
- Sulfur content of oils from the Qusaiba shale is less than 0.1
weight percent. In contrast, oils from Jurassic carbonate source rocks are
commonly greater than 1.0 weight percent sulfur.
2) Arab D reservoir accounts for most of the Jurassic oil
production in the Arabian-Persian
Gulf region, forming many
super-giant and giant fields.
- It is in close stratigraphic position above the Tuwaiq Mountain
and Hanifa source rocks; and
- Is sealed regionally by the Arab-D anhydrite.
Q3: Write short notes:
1) Reservoirs of the Central Arabia Qusaiba-Paleozoic Total Petroleum System
of the greater Ghawar area.
Primary reservoirs of the Central
Arabia Qusaiba-Paleozoic TPS are:
(1) Sandstones of the Permian Unayzah
and Devonian Jauf Formations, and
(2) Basal transgressive marine
sandstones and cyclic dolomitic shelf carbonates of the Late Permian Khuff
Formation.
Other reservoirs include clastics of
the Pre-Qusaiba section that are fault bounded and sourced laterally by
down-faulted Qusaiba Shale Member. These PreQusaiba clastic reservoirs
include:
1)
The Cambrian-Ordovician Saq Sandstone,
2)
Shallow-marine sandstones of the Ordovician Qasim
Formation, and
3)
Upper Ordovician glacial and periglacial clastics of the
Zarqu and Sarah Formations.
2) Traps of the Arabian Sub-Basin Tuwaiq/ Hanifa-Arab Jurassic Total
Petroleum System
Traps and trap styles of the Arabian Sub-Basin Tuwaiq/ Hanifa-Arab TPS are
similar to those discussed in the equivalent "Traps and Trap Styles"
section for the Central Arabia Qusaiba-Paleozoic TPS.
Basement structures in the area of the
Central Arabian intraplatform sub-basin controlled much of the deposition and
subsequent structural growth during the Jurassic. Traps include:
(1) Anticlines related to basement
block faulting;
(2) Domes from tectonic salt pillows or
other halokinetic deformation;
(3) Combined structural traps such as
salt-assisted fault block traps; and
(4) Combined structural/stratigraphic
(facies) traps.
Major trap formation and modification
of the Arabian Sub-Basin Tuwaiq/Hanifa-Arab TPS are a result of the First
(Early) and Second (Late) Alpine Orogenic Events of Oman.
The Early Alpine Orogeny during the Late Cretaceous
was associated with the collision event that led to the emplacement of the
Ophiolite Complex in Oman,
and the Late Alpine Orogeny during the middle to late Tertiary was associated
with the opening of the Red Sea and collision of Arabia and Eurasia.
3) The D3B zone.
Reservoir
sandstones of the Devonian Jauf Formation are capped by a very distinctive
shaly unit informally referred to as the "D3B" stratigraphic marker
or zone.
4) Seal Rocks of the Paleozoic and Jurassic
sections in greater Ghawar area.
Seal
Rocks
- Impermeable units within the Permian lower
Khuff Formation combine to form the primary seal for clastic reservoirs
of the underlying Unayzah Formation. These impermeable anhydrites and
carbonate rocks, and shale beds of the Khuff Formation also constitute the
major regional seal for the Central Arabia Qusaiba-Paleozoic TPS.
- Shales and tight carbonate rocks of the basal
Khuff were deposited over a widespread area during the Late Permian
sea-level rise. The basal Khuff forms the top seal to the Permian Unayzah
reservoir in the southern Ghawar area.
- The basal Khuff also forms the top seal to the
Devonian Jauf reservoirs in unconformity-related traps at Ghawar.
Hercynian faults are also important as lateral seals in controlling
hydrocarbon accumulations in the Ghawar area.
- The Khuff Formation also forms the seal for
hydrocarbon accumulation in Unayzah reservoirs in updip, oil and gas
fields of central Arabia where the
Qusaiba source rock is immature.
- At Abqaiq field, the Hanifa is separated from
the Arab D reservoir by impermeable carbonates of the Jubailah Formation.
- Seal rocks for the major Arab Formation
carbonate-rock reservoirs of the Arabian Sub-Basin Tuwaiq/Hanifa-Arab TPS
are anhydrite beds of the Arab and Hith Formations.
- The
Qusaiba source rock was thermally mature by the Late Jurassic in the
deepest parts of the sedimentary basin in central Arabia;
hydrocarbon expulsion began in
the Early Cretaceous about 120 Ma.
Q1: Discuss the following: (15
Marks)
1) Tectonic evolution and structural setting of the Arabian
Plate.
2) Sedimentary basins of the Middle East.
3) The concept of Petroleum system.
Q2: Explain reasons?
(8 Marks)
1) Differences between Paleozoic oils derived from
clastic Qusaiba Member source beds and
those
generated from younger, carbonate source beds of Jurassic and Cretaceous age.
2) Arab D reservoir
accounts for most of the Jurassic oil production in the Arabian-Persian
Gulf region, forming many super-giant and
giant fields.
Q3: Write short notes:
(17 Marks)
1) Reservoirs of the Central Arabia Qusaiba-Paleozoic Total Petroleum System of
the
greater Ghawar area.
2)
Traps of the Arabian
Sub-Basin Tuwaiq/Hanifa-Arab
Jurassic
Total Petroleum System
3)
The D3B zone.
4)
Seal Rocks of the Paleozoic and Jurassic sections in the greater Ghawar area.
II. Complete the
following: (16
marks)
1.
The main structural elements of the Middle East
are ……………………………,
……………………………………….., ………………………………………,
………………………………………………………………… .
2. The main sedimentary basins and sub-basins
in the Middle East are ……………..
…………………………………………, …………………………………….
…………………………………………., …………………………………….
…………………………, ……………………................................................,
……………………………………………………………………., …………
………………………………………………., ……………………………….
……………………………………………, and ………………………………
…………………………………………….. .
3.
The main platforms in the Middle East are ………………………………………..
………………………………….., …………………………………………….
…………………………, and ………………………………………………….. .
4. Oil and Gas Seeps in Saudi Arabia
include ………………………………………..
………………………………………………….., …………………………….
………………………………………. And ……………………………………..
………………………………………………………………………………… .
5. The first oil
discoveries in the Middle East were
made by the …………… in year………… in southwestern ………… at …………………………………
Anticline.
6. In Saudi Arabia, the first oil
field is the …………….. Field was discovered in …………, the Abu
Hadriya Field was found in …………, and the Abqaiq and Qatif Fields were
discovered in …………..
7. Most of the hydrocarbon production in
the Middle East comes from …………
…………, ……………………….., …………………………….., ……………..
………., …………………., ………………………………… and ………………
……………………………. .
8. Large volumes of gas are present in the Late Permian ………….
Formation and its equivalent formations in …………………., ……………………………….,
…………………………., ……………………….. and……………………….
9. For oil in the Middle
East, the most prolific reservoirs are the Upper Jurassic ………………………………………...
formations in ……………………,
……………………………., ………………………………… and …………
……………………….. .
10. In Saudi
Arabia and adjoining regions in the Middle East, the early Silurian ……………………….. Formation is
the principal Paleozoic source and it generated hydrocarbons throughout the
Mesozoic and in the Cenozoic.
11. The most important oil-reservoir
rocks in the Middle East at least 80% are …………………, and the 20%
are ………………… and most important gas-reservoir rocks 95% are ………………., and the 5%
are …………………….
12. In the Middle East, the
recoverable oil and gas in the main producing countries shows that
Cretaceous rocks host ………% of the recoverable oil, and Paleozoic rocks
host ……….% of the recoverable gas.
13. The principal cap rock
in the Middle East is ……………………, which
formed during Permian to early Miocene; and the ………….. which
formed mostly during the Cretaceous.
14. The Zagros Basin
containing ………………. of the world's oil and …………….. of the world's
gas in a narrow belt some …………….. km long and …… to ………..km wide.
15. In Iraq,
there are more than ……. commercial oil fields, ……
commercial gas discoveries, ……..oil discoveries, The estimated
volume of the oil discovered in Tertiary reservoirs is about …….. B.bbl,
in Cretaceous reservoirs around ………. B.bbl and in Paleozoic
reservoirs about ……B.bbl.
16
In Iran, the large
oil and gas accumulations of the Zagros Fold Belt are all associated
with ……………… reservoirs and the most important are the ……………. Limestone
of ……………….. age, followed by the limestone of Albian-Campanian ………………...Group.
Modal Answer
I. Complete the following:
1.
The main structural elements of the Middle East
are sedimentary basins, Arches, and Transform
Faults & Normal Faults.
2. The main sedimentary basins and sub-basins
in the Middle East are Tabuk sub-basin in Saudi Arabia, Widyan
sub-basin in Saudi Arabia, Sirhan sub-basin in Jordan, Rub A1 Khali and
Ras A1 Khaimah sub-basins in Saudi Arabia - U.A.E, Zagros Basin in Iran,
Palmyra and Sinjar sub-basins in Syria-Iraq, The Mesopotamian sub-basin in
Iraq and Red Sea and Gulf of Aden sub-basin in Saudi Arabia-Yemen.
3.
The main platforms in the Middle East are Southeastern
Arabian platform, Northern Arabian Platform, and Northwestern
Arabian Platform.
4. Oil and Gas Seeps in Saudi Arabia include a 5-cm stringer of
bitumen in anhydrite overlying the Arab producing horizons, a tar seep was
found at Dahl Hit in a small solution cave near Riyadh
and scattered oil seeps along the Red Sea
coast, especially in the Farasan and Dahlac islands.
5. The first oil discoveries in the Middle
East were made by the D'Arcy Company in 1901 for work in southwestern
Iran
at Masjidi-Sulaiman Anticline.
6. In Saudi Arabia, the first oil field
is the Dammam Field was discovered in 1938, the Abu Hadriya Field
was found in 1939, and the Abqaiq and Qatif Fields were discovered in 1940.
7. Most of the hydrocarbon
production in the Middle East comes from Iraq,
southwestern Iran, eastern Saudi Arabia, Kuwait,
Qatar, the U.A.E. and Oman.
8. Large volumes of gas are
present in the Late Permian Khuff Formation and its equivalent formations
in Saudi Arabia, Bahrain, Qatar,
Iran
and the U.A.E.
9. For oil in the Middle East,
the most prolific reservoirs are the Upper Jurassic Dhruma and Arab
formations in Saudi Arabia,
Bahrain, Qatar and Abu
Dhabi.
10. In Saudi Arabia and adjoining regions in the Middle East, the early Silurian Qusaiba (Shale)
Formation is the principal Paleozoic source and it generated hydrocarbons
throughout the Mesozoic and in the Cenozoic.
11. The most important
oil-reservoir rocks in the Middle East at
least 80% are carbonate, and the 20% are sandstone and
most important gas-reservoir rocks 95%
are carbonate, and the 5% are sandstone.
12. In the Middle East, the recoverable oil and gas in the main
producing countries shows that Cretaceous rocks host 51% of the
recoverable oil, and Paleozoic rocks host 50% of the gas.
13. The principal cap rock
in the Middle East is anhydrite, which
formed during Permian to early Miocene; and the shale,
mostly Cretaceous performs the same seal.
14. The Zagros Basin containing two-thirds
of the world's oil and one-third of its gas in a narrow belt some
2,500 km
long and 5-700 km
wide.
15. In Iraq, there are more than 66 commercial
fields, 8 commercial gas discoveries, 17 oil discoveries, The
estimated volume of the oil discovered in Tertiary reservoirs is about 33.8
B.bbl, in Cretaceous reservoirs around 107.1 B.bbl and in Paleozoic
reservoirs about 1 B.bbl.
16. In Iran,
the large oil and gas accumulations of the Zagros Fold Belt are
all associated with carbonate reservoirs and the most important
are the Asmari Limestone of Oligo-Miocene age, followed by the limestone
of Albian-Campanian Bangestan Group.
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