Paleozoic in saudi arabia

Controls on hydrocarbon properties in a
Paleozoic petroleum system in Saudi Arabia
Exploration and development implications.
By
Abd Al Rahman Ibrahim Soliman,
BSc of Geology/ Geophysics,
Faculty of science, Alexandria University.
abdalrahmanibrahim209@gmail.com

2
Agenda
Paleozoic in Saudi Arabia
• Introduction
• What we need to success?
• Importance of Organic Geochemistry
• Saudi Arabia oil& Gas Fields
• Economic Importance of Pre-Khuff Reservoirs
• Case study (Ghazal Field)
o Unayzah Play
o Devonian Play
o Cambrian-Ordovician Plays
• Discussion
• References

3

4
Introduction
• Deep Paleozoic reservoirs in Saudi Arabia
are traditionally regarded as gas plays, and
the latest oil discoveries in Permian–
Carboniferous Unayzah (UNYZ) sandstone
reservoirs along the southern downdip
flank of the structurally complex Ghazal
(GHZL) field were thus unpredicted.

5
Introduction
• This highlighted the need for a thorough
assessment of possible effects of different
processes on hydrocarbon distribution to
improve prediction and reduce uncertainty.

6
Introduction

7
Introduction

8
Introduction

9
Introduction
• Special emphasis is given to assess if the
oils and gas condensates are products of
multiple filling events or phase
fractionation; in other words, to test if the
gas condensates are thermal
or evaporative products

10
Agenda
• What we need to success?
o Unayzah Play
o Devonian Play
• Discussion
• References

11
What we need to success?
• Successful prediction of oil versus gas
occurrence in the subsurface demands an
integrated geological and geochemical
approach. Assessment of controls on
hydrocarbon expulsion maturity, migration
pathways, emplacement, and segregation
is a key to successful petroleum system
analysis.

12
A Rube Goldberg View
of a Hydrocarbon System
A “Kitchen”
Where Organic
Material Is
Cooked
A “Container”
From Which
Oil & Gas
Can Be
Produced
“Plumbing” To Connect
the Container to the Kitchen
Correctly
Placed
Wells

13
0
2
4
6
8
Oil & Gas
Generation
Window
Gas
Generation
Window
Depth(km)
Source
Reservoir
Trap & Seal
Migration
Gas & Oil
No More
HC Generation

14
Trap A
Trap B
Synclinal
Spill Point
Fault Leak
Spill Point
1. Early Charge: Some Oil, Minor Gas
2. Peak Charge: Significant Oil, Some Gas
Gas Cap
Displaces Oil
Oil Spilled
from Trap A
to Trap B
Oil Spills
Up Fault
3. Late Charge: No Oil, Significant Gas

15
Agenda
o Unayzah Play
o Devonian Play
• Discussion
• References

16
Importance of Organic Geochemistry
• Petroleum geochemistry deals with oil
typing and genetic relationships, maturity,
alteration, charge history, and the
generating source rocks. Oil geochemistry
can significantly reduce exploration and
development risk when integrated with
available geological and engineering data.

17
• For example, geochemistry of oil samples
can be used to identify the source rock and
likely migration pathways, or it can be
used to assess reservoir
compartmentalization, thereby optimizing
well placement and maximizing
hydrocarbon recovery.

18
• For example, geochemistry of oil samples
can be used to identify the source rock and
likely migration pathways, or it can be
used to assess reservoir
compartmentalization, thereby optimizing
well placement and maximizing
hydrocarbon recovery.

19
• Primary controls on oil versus gas (gas-to-oil ratio
[GOR] or condensate-to-gas ratio [CGR]) distribution
in a basin include the
 type and thermal maturity of the source rock,
 the charge history, and
 the regional distribution of carrier, reservoir, and
seal beds.
 The pressure, volume, and
 temperature conditions in the reservoir influence
GOR or CGR during hydrocarbon accumulation,

20
• whereas several secondary alteration processes
influence hydrocarbon composition after trapping. The
main post accumulation alteration effects on
hydrocarbon composition and distribution include
 oil cracking,
 water washing,
 biodegradation,
 segregation (displacement), and
 phase separation caused by pressure drop or
gas influx.

21
Agenda
o Unayzah Play
o Devonian Play
• Discussion
• References

22
Saudi Arabia oil& Gas Fields

23
Saudi Arabia oil& Gas Fields production

24
Agenda
o Unayzah Play
o Devonian Play
• Discussion
• References

25
Economic Importance of Pre-Khuff Reservoirs
• 25% Gas Prod. f/Pre-Khuff – Mostly Unzy
• Unzy’s Most Abrasive & Problematic to
Drill
• Gas Demand will inc. to 12 bscfd by 2025
• 50-55% of this must come from the Pre-
Khuff
• Currently Drlg. 47 Gas Wells/year w/18
Rigs
• Utilizes three Workover Rigs & one Snub.

26
Economic Importance of Pre-Khuff Reservoirs
• Pre-Khuff – Formations of Lower Permian
Age or older deposited before the Khuff
Include the Unayzah, Jauf, Tawil,
Sharawra, Qusaiba, Sarah, Qasim and
Saq
• Mainly hard and ultra abrasive sandstones
interbedded with siltstones and shales
Shales often unstable requiring 1500 psi
overbalance to mitigate tight hole.

27
Agenda
o Unayzah Play
o Devonian Play
• Discussion
• References

28
Ghazal Field

29
Ghazal field

30
Ghazal field
• The Ghazal field, on production since
2003, was originally believed to be a gas
condensate producer (CGR < 170 bbl. of
oil per million standard cubic feet of gas
[bbl./ MMSCF])

31
Ghazal field
• The Paleozoic clastic petroleum system in
central Saudi Arabia includes two main
reservoirs:
1. The Permian–Carboniferous Unayzah
Formation (primarily aeolian and
fluvial sandstones), which contains the
principal pre- Khuff hydrocarbon
reservoirs in the southern Ghawar region,
and

32
Ghazal field

33
Ghazal field

34
Ghazal field
2. the Devonian Jauf Formation (shallow-
marine sandstone) in the northern Ghawar
area where the Unayzah is completely
missing and the Khuff Formation rests
unconformably on sub-Hercynian
sediments .

35
Ghazal field

36
Ghazal field

37
Unayzah Play

38
Unayzah Play
• In Saudi Arabia, the potential of the
Permian Unayzah was confirmed in 1979
by a gas discovery in the Qirdi field.
• The Unayzah play became much more
significant in 1989, when super light oil
was discovered in Hawtah-1 in central
Saudi Arabia. Another 16 Unayzah fields
have been discovered in

39
Unayzah Play
• the past decade. The fields are structural
closures along Hercynian basement-cored
uplifts, that may be transpressional in
origin.
• Moreover, the stratigraphic variability of the
Unayzah, influenced by paleotopography
and the continental environments of
deposition, lends a stratigraphic
component to entrapment.

40
Unayzah Play
• The Unayzah oils range from 48o to 53o
API gravity and their gas/oil ratio (GOR) is
less than 90 m3/m3.
• The low GOR is attributed to solution of
methane in waters in an active
hydrodynamic system driven by influx of
meteoric water from outcrops along the
western edge of the basin.

41
Unayzah Play
• The Silurian source rocks in central Saudi
Arabia are immature, and the Unayzah oils
were evidently generated in the deeper
parts of the basin and migrated about 200
km westwards towards the basin margin
• The Unayzah and overlying basal Khuff
clastics are composed of alluvial, fluvial,
and eolian facies.

42
Unayzah Play
• The Unayzah includes three sandstone
reservoirs, designated informally as A, B,
and C, which are separated by silt- and
mudstone.
• The sandstone reservoirs are laterally
discontinuous, and their quality varies
depending on sorting and the amount of
diagenetic quartz, kaolinite, illite/smectite
cement.

43
Unayzah Play
• Intergranular porosity ranges up to 30%
and permeability up to one darcy,
• particularly in the aeolian sandstone facies.
The top seal are transgressive shales at
the base of the overlying Khuff Formation.
• The Unayzah play was extended during
the last decade to target gas in the deeper
basin (>3,700 m)

44
Unayzah Porosity vs. Abrasivity from Offset Core

45
Unayzah Play
• near facilities in eastern Saudi Arabia. The
gas exploration campaign has resulted in
the discovery of six additional Unayzah
gas/condensate fields near Ghawar field,
such as Waqr and Tinat.

46
Unayzah Play

47
Unayzah Play
• The Unayzah deep gas play presents additional
challenges, which include poor seismic imaging
of
• the Paleozoic section and abrupt variation in
reservoir quality due both to stratigraphy and
diagenesis.
• The problems of deep seismic imaging and
reservoir heterogeneity are both being
addressed by the acquisition of high-effort, 3-D
seismic surveys to reduce reservoir and trap

48
Unayzah-A Core from Tinat-6
• Abrasive
• Not as
Hard as
UNZY-B
•Friable

49
Unayzah Play

50
Agenda
o Devonian Play
• Discussion
• References

51
Devonian Play
• Gas in the Devonian Jauf sandstone was
initially discovered in 1980 by a deeper
pool test in the north Ghawar field.
Subsequent tests showed that the
Devonian section was mostly eroded from
the crest of the structure.

52
Devonian Play
• The discovery in 1994 of Jauf gas in a
combination structural-stratigraphic trap
along the flank of the Ghawar structure
was a major exploration success,
especially in light of the poor seismic
imaging of the pre-Khuff section

53
Devonian Play
• The Jauf reservoir consists of shallow marine
sandstones with relatively high porosities (up to
25%).
• This is unusual given their burial to over 4,300
m. Unlike other pre-Khuff siliciclastic, which
have undergone extensive silica cementation,
the Jauf reservoir is weakly cemented with
authigenic illite that coats grain surfaces, which
apparently has inhibited quartz cementation
and preserved porosity.

54
Devonian Play
• The abundant illite also lowers resistivity
values due to the excess bound water and
the high cation
• exchange capacity of illite. This can cause
pessimistic water saturation estimates and
lead to potentially bypassed low-resistivity
pay zones

55
Agenda
• Discussion
• References

56
Cambrian-Ordovician Plays
• Several discoveries have been made in
Upper Ordovician structural traps,
including Dilam and Abu Jifan in central
Saudi Arabia, Kahf and Jalamid in northern
Saudi Arabia, and Wadi Sirhan and Risha
in Jordan

57

58
• These, mainly gas fields, are sourced and
sealed by the overlying Silurian shales. Where
the Silurian is missing due to Hercynian
erosion, the Permian Khuff forms the seal.
• The Ordovician reservoirs are generally of poor
quality. In the deeper basins, the sandstones
have low porosities and permeabilities due to
compaction and extensive cementation by
quartz overgrowths

59
• during burial. Petrographic studies indicate
that any significant porosity is secondary,
due primarily to dissolution of early
intergranular carbonate cement. The early
carbonate cementation was localized in
areas where Hercynican erosion placed
the Khuff carbonates unconformably above
the Ordovician.

60
• This cement was probably derived from the
Khuff, and occurred at shallow depths
before the sandstones underwent
significant compaction. The subsequent
dissolution of carbonate cement preceded
hydrocarbon migration into the reservoirs.

61
Agenda
• Discussion
• References

63
Agenda
• References

64
Reference
• Breakthrough Horizontal Drilling Performance in Pre-Khuff Strata with
Steerable Turbines, Mike Simpson, Shaohua Zhou, Dave Treece,
Carlos Rondon, Tom Emmons, Saudi Aramco; Craig Martin Sii-Neyrfor
and Mohammad Tahir, Diamant Drilling Services.
• GeoArabia, Vol. 6, No. 3, 2001, Gulf PetroLink, Bahrain
• Controls on hydrocarbon properties in a Paleozoic petroleum system in
SaudiArabia: Exploration and development implications; Khaled R.
Arouri, Pierre J. Van Laer, Mark H. Prudden, Peter D. Jenden, William J.
Carrigan, and Adnan A. Al-Hajji

65
Agenda

Paleozoic in saudi arabia

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