Certification: Indian School of Petroleum & Energy

1. Natural Gas
• Utilised as Fuel for > 150 years.
• Difficult to store and transport compared to liquid fuels.
• Used only where it is produced, Rest being burned off, once upon a time.
• Development of facilities like large diameter high pressure pipelines,
compressors, gas storage in the Reservoirs etc. The demand of natural gas and
development of technology required to produce and transport.
• Increases rapidly as feedstock for Petrochemical industries.
Introduction:

2. Geographical Occurrence:
Requirement for commercial accumulation:
• A source: that is, material from which the petroleum is formed.
• Porous and permeable beds in which the petroleum may migrate and accumulate
after being formed.
• A trap or subsurface condition restricting further movement so that it may
accumulate in commercial quantities.
Natural gas & Oil:
• Generated from organic matters.
• Under the influence of increasing temperature and time.
• Organic matter can be divided into TWO broad categories:
1. Derived from organisms growing on the land surface  Terrestrial  Produces Natural
gas and waxy crude.
2. Derived from organisms growing in the water  Aquatic  Produces normal crudes

3. • Depth is important to which crude oil or natural gas may occur.
• Rivers - played a critical role in transporting terrestrial material to the
depositional environment.
• River Deltas are very gas-prone depositional environments.
• The oldest and deepest sediments were deposited in the continental rift.
• Increasingly marine sediments containing greater amounts of aquatic matters
deposited above the terrestrial material.
• So that a vertical sequence develops with the gas-generating organic matter at
the bottom and the oil-generating material at the top.
Geographical Occurrence: contain.

4. Modification by Migration & Burial:
• After formation of Oil and gas it may be remobilized – Secondary migration.

5. • Natural Gas can occur either associated or non-associated with oil.
• Trap 1 – Non-associated gas reservoir.
• Trap 2 – An associated gas reservoir.
• Composition varies with Temperature and Pressure.

6. • As Temp. increases the hydrocarbons readjust toward equilibrium.
• Readjustment causes redistribution of hydrogen – gives methane and a solid carbon
rich residue.
• Oil first changes to condensate then to wet gas and finally to dry gas.
• At depth beyond 40,000 ft Methane can remain stable under certain condition.
- Survival of Methane is influenced by reservoir lithology with fairly cool, clean
sandstones.
- Found that Methane has less stability in deep carbonates.
- Natural gas may exist at greater depth provided porous and permeable reservoir exists
at that depth.

7. PDO Main Gas fields and distribution :
BARIK OIL STN.
SOHAR
MUSCAT
SAIH RAWL
YIBAL
SUR
QARN ALAM
SAIH RAWL
OIL STATION
BARIK
AL GHUBAR STN,
16” Condensate Export
48” Gas Export
20” Gas Export
36” Gas Export
16” Gas Export
28”Interlink
14” Condensate
32”
Gas
WATER DISPOSAL
MAINOILLINE
Central Processing Plant
24” TO SALALAH
SALALAH
32”
CPP

8. SAIH RAWL
BARIK
M
AIN
OIL
LINE
QARN
ALAM
48” TO SUR Oil to
MUSCAT
CPP
IPS
32”Gas
14”
Condensate
SAIH RAWL
OIL STATION
W
ater
Disposal
BARIK
OIL
STATION
W
ater
Disposal
OLNG
24” To SALALAH
16” CONDENSATE
CENTRAL OMAN SYSTEM
Handed over to Oman
Gas Co as of 1/1/2002
21-23 million Sm3/d
28” INTERLINK
44 million Sm3/d
44 million Sm3
/d
20”
16”
GOVERNMENT GAS
SYSTEM
32” TO SOHAR
Muscat
Sohar
Yibal
Gas Department
36” GAS
Salalah

9. Gas field Reservoir:
Saih Rawl
• Rich gas at the barik Sandstone level(200m)
• Dry gas in the miqrat Sandstones(100m)
• In Saih Rawl South the Barik and Miqrat
form a number of stacked reservoir/seal
pairs.
• The Graben and Main area contain single
gas columns.
•With start of production the near well-bore
region drops quickly below the dew-point
causing condensate drop-out.
• which impairs the total gas and condensate
that can be achieved from the well.
• To reduce the effect, the wells are
hydraulically farced.

10. • The well diagrams show the monobore completion (Phase I) and the cement
completion (new design for Phase II)
• In most of the Saih Rawl wells three-four fracs are placed to connect to the full gas
column.
• The wells are big energy producers: at rates of 1.5 - 2.5million m3/day gas and
700- 1200 m3/day of condensate

11. Gas field Reservoir:
Barik Fields:

12. • Rich gas and condensate are produced to the Barik Gas Gathering Station (BK - GGS
from hydraulically fractured wells.
• Well rates at start up of field production ranged from 2.2 - 1.0 MM m3/day gas with
an associated condensate gas ratio (CGR) of 1100 m3 condensate/MM m3 gas.
• Barik field is produced under depletion drive.
• The reservoir pressure is continually declined.
• Results condensate "drops out" of the gas in the reservoir.
• This condensate remains trapped in the reservoir acting as a barrier to gas flow and
reducing gas and condensate rates.
• Gas production rates from Barik wells have declined by as much as 65% in the first
1-1/2 years of production due to a combination of this phenomenon called
'liquid drop out' and pressure depletion.
Barik Fields:Cont.

13. Hydraulic Fracturing:
• This half century-old technology is used in oil and gas production.
• Is made to maximize the production of oil and gas
• Allows oil or natural gas to move more freely from the rock pores to a producing well
• To connect many pre-existing fractures and flow pathways in the reservoir rock with
a larger fracture.
• The man-made or hydraulic fracture is formed when a fluid is pumped down the
well at high pressure for short periods of time (hours).
•The high pressure fluid (Usually water with some specialty high viscosity fluid
additives) exceeds the rock strength and opens a fracture in the rock.
• A propping agent, usually sand carried by the high viscosity additives is pumped
into the fracture to keep them from closing when the pumping pressure is released.
• The viscosity fluid becomes a lower viscosity fluid after a short period of time.
• Both the injected water and the now low viscosity fluids travel back through the
man-made fracture to the well and up to the surface.

14. Gas field Reservoir:
Yibal Gas Fields
• Since 1978, Yibal Natih
reservoir has provided gas to
the Batinah coast.
• The reservoir is a fractured
carbonate and it spreads 77
km2.
• All Government Gas
producers are drilled on the
crest, within 1 km radius of
the Government Gas Plant.
• The reservoir behaves like
a single tank.
• Oman’s biggest oil
reservoir is located
underneath: the Yibal
Shuaiba.

16. • In December 1997 a novel barefoot horizontal well was drilled with a 9.5/8” tubing,
See drawing.
• The well was hooked-up in 1998 and flowed 3.8 million m3.
• The successful implementation of this new well design will significantly reduce
future development costs.
• Full Field Development Plan is currently being designed.
• All future wells will be of same design or better than the last Y-441 horizontal big
producer.
• With growth in demand due to population and industry needs, and with depletion of
the reservoir pressure, 2nd stage well head compression is planned for the year 2005.
• Yibal Natih continue to be the sole source of gas for power generation to the
Sultanate.

17. Oman’s (PDO Operated) Gas FieldsOman’s (PDO Operated) Gas Fields
Not yet in operatrion
Already in operatrion

18. Gas ReservesGas Reserves By Region (By Region (end 2001end 2001))

19. Characteristic of NATURAL GAS
• Natural gas is a mixture of hydrocarbon gases with some impurities.
i.e. mainly nitrogen (N2), hydrogen sulfide (H2S), and carbon dioxide (CO2).
• Gases contains H2S or C02 or both are called sour or acid gases.
• These impurities must be removed before the gas is used as a fuel.
• The hydrocarbon gases are:
- Methane,
- Ethane,
- Propane,
- Butanes,
- Pentanes, and
- Small amounts of hexanes, heptanes, and some heavier fractions.
• Natural gas is normally considered to be a mixture of straight chain or paraffin
hydrocarbon compounds.
• However, occasionally cyclic and aromatic compounds occur in a natural gas.
• The molecular structures of some of these are shown in the figure.
• The general formula for the paraffin hydrocarbons is CnH2n+2,
where n is the number of carbon atoms.

20. C
H
H
H
H
C CCH
H H H
H
HHH
C
H
H
H
H
CCH
H H
HH
H
C CCH
H H H
H
HHH
C CC
H H H
H
HHH
C
H
H
H
C CC
H H H
H
HHH
C
H
H
H
H
H C
C CC
H H H
H
HHH
C
H
H
H
H
CC
H
H
H
HYDROCARBON MOLECULES
LIGHT HEAVY
METHANE
CH4
ETHANE
C2H6
PROPANE
C3H8
BUTANE
C4H10
PENTANE
C5H12
HEXANE
C6H14
HEAVY or LIGHT denotes the number
of CARBON ATOMS
General
formula for
Alkanes
CnH2n+2

21. Other Sources of Gaseous Fuel:
• Liquefied Natural Gas: LNG is essentially methane
- liquefied at atm. pressure by cooling it to -162 C.
- reduces the volume by 623: 1
- transported in large tankers - 750,000 barrels or more of LNG.
• Coal Gasification: Synthetic gas from coal - investigated in the United States,
- usually low in heating value as compared to natural gas.
- but the commercial viability has not been demonstrated.
• Substitute Natural Gas. Substitute natural gas (SNG) can be made from liquid
Petroleum feedstock such as naphtha, crude oil, propane, and butane.
- the cost is extremely high in comparison to natural gas at its present price.
• Tight Formation Gas: Gas from very low permeability formations
- In order to recover fracture the formation with a nuclear blast,
- but so far this technique has not proved feasible.
- other method is massive hydraulic fracturing, but so far has not proved
feasible.

22. Gas from Geopressured Aquifers: High pressure brine in geopressured
aquifers may contain 30 to 40 scf of natural gas per barrel of water.
- located in a band that extends from Florida to Texas along the Gulf of
Mexico.
- Estimates of the gas in place range from 1000 to 3000 Tcf.
- But no commercial method of recovering this gas had been developed.