This module is an introduction to natural gas resources. It gives description on source, reservoir and cap rocks as well as suitable environments for natural gas generation, migration and accumulation.

1. Introduction to Natural Gas
Utilization of Natural GasUtilization of Natural Gas
Resources TrainingResources Training
MoEMoE
Morogoro-TanzaniaMorogoro-Tanzania
By: Nsulangi, P.T
Contacts: +255 686 195 449
nsulangi@gmail.com
Masanja,A.M
Contacts: +255 745 086 978
abel.masanja@yahoo.com
2020thth
-21-21stst
, December 2018, December 2018

2. Lecture Contents
 Introduction to Natural Gas (NG)
 Gas source rocks
 Gas reservoir rocks
 Gas generation, migration and accumulation.
 Composition of Natural Gas.
 Summary and Conclusion
Natural Gas_01_Tanzania2

3. Chapter Objectives
 To describes source, reservoir and cap rocks and
the suitable environments for natural gas
generation, migration and accumulation.
Natural Gas_01_Tanzania3

4. Natural Gas (NG)
 Natural Gas (NG)
– Natural gas is a mixture of combustible gases
formed underground by the decomposition of
organic materials in plant and animal.
 Natural Gas is formed when layers of
decomposing plant and animal matter are
exposed to intense heat and pressure under
the surface of the Earth over millions of years.
Natural Gas_01_Tanzania4

5. Natural Gas (NG) cont.…
Natural Gas_01_Tanzania5
CompressionCompression
HeatHeat
DecompositionDecomposition

6. Natural Gas (NG) cont.…
 The main component of Natural Gas (NGNG) is
methane (CHCH44), other components includes:
– Methane; CHCH44 : 70-90%: 70-90%
– Ethane; Propane, Butane: 0-20%0-20%
– Water vapor, Hydrogen sulfide, Carbon dioxide,
Nitrogen, and Helium: < 10%10%
Natural Gas_01_Tanzania6
Note:Note:
The composition of Natural Gas (NG) depends on theThe composition of Natural Gas (NG) depends on the
chemical compositionchemical composition of decomposed materials inof decomposed materials in
plants and animals.plants and animals.

7. Gas Source Rocks
 A sources rocks is rich in organic matter which, if
heated sufficiently, will generate oil or gas.
 Typical source rocks, usually shales or limestones,
contain about 1% organic matter and at least 0.5%
total organic carbon (TOC), although a rich source
rock might have as much as 10% organic matter.
 Rocks of marine originmarine origin tend to be oil-proneoil-prone,
whereas terrestrial source rocksterrestrial source rocks (such as coal)
tend to be gas-pronegas-prone.
Natural Gas_01_Tanzania7

8. Gas Source Rocks cont..
Natural Gas_01_Tanzania8

9. Reservoir Rocks
 Reservoir Rocks
– are the rocks that have ability to store fluids inside
its pores, so that the fluids (water, oil and gas) can
be accumulated.
 In petroleum geology, reservoir is one of the
elements of petroleum system that can
accumulate hydrocarbons (oil or gas).
 Reservoir rock must be has good porosity and
permeability to accumulate and drain oil in
economical quantities.
Natural Gas_01_Tanzania9

10. Properties of Reservoir Rocks
cont..
 Reservoir Porosity
– Porosity is the void space in a rock that can store
the fluids.
– Porosity measures on a fluids storage capacity of
the rocks.
Natural Gas_01_Tanzania10
High porosityHigh porosity Low porosityLow porosity

11. Properties of Reservoir Rocks
cont..
 Reservoir Permeability
– Permeability is an fundamental property of a
material that determines how easily a fluid can pass
through it.
– Permeability measures on how easily rock materials
will transmits fluids due to the changes in pressure.
Natural Gas_01_Tanzania11
Poor permeabilityPoor permeabilityGood permeabilityGood permeability

12. Gas/Hydrocarbon Generation
 Natural Gas (NG) or Petroleum is generated
from productive source beds which have high
organic carbon content.
 This high organic carbon content resulted from
the burial of plants and animals.
 Since all plants are not of equal carbon content
and so do animals, the CC range of the
petroleum change when the carbon source
changes.
Natural Gas_01_Tanzania12

13. Gas/Hydrocarbon Generation cont.
 Maturation is the ability of the rock to generate
hydrocarbons, and indicates its maturity.
Therefore, the more the rock quality is, the more
mature it is.
 Maturation occurs through millions of yearsmillions of years in
which diagenesis and catagenesis processes take
place.
 About 10 to 20% of petroleum is formed during
diagenesis.
Natural Gas_01_Tanzania13

14. Gas/Hydrocarbon Generation cont.
 Most petroleum is formed during the catagenesis
and metagenesis of the residual biogenic organic
matter.
Natural Gas_01_Tanzania14

15. Natural Gas/Petroleum Generation
Process
 There are three stages for generation of
petroleum products from the decomposed
materials;
1.0 Diagenesis
– During diagenesis there is shallow burial of organic
matter at near normal temperature (<500
C) and
pressure as well as some decay.
– Methane (CH4), carbon dioxide (CO2), and water
(H2O)are released leaving behind the complex
hydrocarbon called kerogen.
Natural Gas_01_Tanzania15

16. Diagenesis Process
Natural Gas_01_Tanzania16
<50o
C
Products:Products:
-Biochemical Gas-Biochemical Gas

17. Natural Gas/Petroleum Generation
Process cont.…
2.0 Catagenesis
– Deeper burial results in increased temperature
(600
C- 200o
C) and pressure.
– Petroleum is released from the kerogen.
– First oil is released (2-3 km depth) and second
gas is released (3-5 km depth).
Natural Gas_01_Tanzania17
Cracking reactions and condensation reactionsCracking reactions and condensation reactions
takes place at this stage.takes place at this stage.

18. Categenesis Processes
Natural Gas_01_Tanzania18
200o
C
60o
C
Products:Products:
-Gas-Gas
-Oil-Oil

19. Natural Gas/Petroleum Generation
Process cont.…
3.0 Metagenesis
– Takes place at temperatures over 200◦
C
(>2000
C) and is considered to be a type of very
low-grade metamorphism.
– The only hydrocarbon that is released during
this phase is methane (Gas).
– At this point the petroleum has matured enough
to migrate to traps.
Natural Gas_01_Tanzania19

20. Metagesis Processes
Natural Gas_01_Tanzania20
>200o
C Products:Products:
-Natural GasNatural Gas

21. Natural Gas/Petroleum Migration
 Migration
– Movement of petroleum from source rock toward a
reservoir or seep.
 Causes of Petroleum migration
– Kerogen expansion
– Increase in pressure and
– Hydrocarbon expulsion out of source rock
Natural Gas_01_Tanzania21

22. Petroleum Migration
Natural Gas_01_Tanzania22

23. Type of Hydrocarbon Migration
 There are four types of petroleum migrations which
are:
– Primary migration
– Secondary migration
– Tertiary migration and
– Remigration
 Primary migration
– refers to the movement of hydrocarbons from source
rock into reservoir rock or
– Loss of hydrocarbons from the source rock.
Natural Gas_01_Tanzania23

24. Type of Hydrocarbon Migration
cont..
 Secondary migration
– refers to the subsequent movement of hydrocarbons
within reservoir rock; the oil and gas has left the
source rock and has entered the reservoir rock.
 Tertiary migration:
– The migration of petroleum accumulation which
trapped in the reservoir to the surface.
Natural Gas_01_Tanzania24

25. Type of Hydrocarbon Migration
cont.
 Tertiary migration:
– The migration of petroleum accumulation which
trapped in the reservoir to the surface.
 Remigration
– Migration from one reservoir position through an
intervening section into another reservoir position in
the same or a different reservoir.
Natural Gas_01_Tanzania25

26. Type of Hydrocarbon Migration
cont.
Natural Gas_01_Tanzania26

27. Petroleum Accumulation
 Petroleum accumulations from the Earth’s
crust can be grouped into conventionalconventional and
unconventionalunconventional ones.
 Unconventional accumulationUnconventional accumulation
– The unconventional accumulation takes place
mostly in source rocks
– Examples
Shale oil and gas and
Coal bed methane
Natural Gas_01_Tanzania27

28. Petroleum Accumulation cont..
 Conventional accumulationConventional accumulation
– The conventional accumulation takes place mostly
in reservoir rocks
– Examples
Sands reservoirs
Natural Gas_01_Tanzania28

29. Conversion Accumulation
Natural Gas_01_Tanzania29
ReservoirReservoir
RocksRocks
Source RocksSource Rocks
Gas producing wellGas producing well Oil producing wellOil producing well
Note:Note:
•For conversion
accumulation
•There is aThere is a
movement ofmovement of
hydrocarbon fromhydrocarbon from
source to reservoirsource to reservoir
rocksrocks

30. Natural Gas Compositions
 Natural gas is a naturally occurring gas
Mixture, consisting mainly of methane (CHCH44).
 The truth is,
– The composition of Natural Gas is different
depending on the location.
– The exact composition at any site will vary among
the different regions and over time.
– Each well has a different Natural Gas composition
and different amounts of each hydrocarbon gases
component.
Natural Gas_01_Tanzania30

31. Natural Gas Compositions cont..
 Gases which may found into the Natural Gas:
– Natural gas is a combustible mixture of hydrocarbonhydrocarbon
gases into a different proportionality.
Ethane (CC22HH66),
Propane (CC33HH88),
 Butane (CC44HH1010), and
Pentane (CC55HH1212)
 The gas that we get as consumers is made up of
almost entirely pure methane
Natural Gas_01_Tanzania31

32. Natural Gas Compositions cont..
Natural Gas_01_Tanzania32

33. Natural Gas Compositions cont..
 When there is almost pure methane, Natural Gas
is considered dry gasdry gas.
 When the heavier hydrocarbons are present, the
gas is considered wet gaswet gas.
Natural Gas_01_Tanzania33

34. Chapter Summary
 The main component of Natural Gas (NGNG) is
methane (CHCH44), which is formed at temperatures
over 200◦
C (>2000
C).
 Whenever there accumulation of Natural Gas,
there is a possibility of getting traps oil and other
petroleum gases, so the government should put
more efforts on research and exploration.
Natural Gas_01_Tanzania34

35. References
 Meissner, F. F. (1991). Petroleum geology of the Bakken Formation Williston Basin,
North Dakota and Montana.
 Passey, Q. R., Bohacs, K., Esch, W. L., Klimentidis, R., & Sinha, S. (2010, January).
From oil-prone source rock to gas-producing shale reservoir-geologic and petrophysical
characterization of unconventional shale gas reservoirs. In International oil and gas
conference and exhibition in China. Society of Petroleum Engineers.
 Caineng, Z., Zhi, Y., Shizhen, T., Wei, L., Songtao, W., Lianhua, H., ... & Jinhua, J.
(2012). Nano-hydrocarbon and the accumulation in coexisting source and
reservoir. Petroleum Exploration and Development, 39(1), 15-32.
 Ma, Y., Zhang, S., Guo, T., Zhu, G., Cai, X., & Li, M. (2008). Petroleum geology of the
Puguang sour gas field in the Sichuan Basin, SW China. Marine and Petroleum
Geology, 25(4-5), 357-370.
 Lucia, F. J. (1995). Rock-fabric/petrophysical classification of carbonate pore
space for reservoir characterization. AAPG bulletin, 79(9), 1275-1300.
 Meissner, F. F. (1991). Petroleum geology of the Bakken Formation Williston
Basin, North Dakota and Montana.
Natural Gas_01_Tanzania35

36. Natural Gas_01_Tanzania36
Any Questions, Suggestions,Any Questions, Suggestions,
Comments, etc.Comments, etc.
THANK YOUTHANK YOU