Coal and petroleum are related in their origin from plant matter, but differ in their state and environment of deposition. Both undergo geological processes that change their composition over time through coalification and kerogen formation. Coals can serve as a source rock for natural gas and, depending on their composition and maturity, may generate oil as well. Key indicators of coal rank and maturity include moisture, volatile content, carbon content, and vitrinite reflectance measured microscopically.

1. COAL AND ITS RELATION TOCOAL AND ITS RELATION TO
OIL AND GASOIL AND GAS
GEM 688 PRESENTATION
BY
OLADELE OLUWASAYO OLUWABUNMI

2. OUTLINEOUTLINE
 INTRODUCTION
 COALIFICATION
 COAL PETROGRAPHY
 KEROGEN
 APPLICATION OF REFLECTANCE MEASUREMENT
 PETROLEUM GENERATION
 COAL AS A SOURCE ROCK
CONCLUSION CONCLUSION

3. INTRODUCTIONINTRODUCTION
Both coal and petroleum are related in terms of;
•Origin: Both originate predominantly from organisms of the plant kingdom
•Geologic processes/Formation: Subjected to the same geological processes
However, they differ based on;
•State of occurrence: coal is found at its site of deposition as a solid, while
petroleum is liquid and migrates from the source beds into porous reservoir rocks
•Environment of deposition: Most coals are deposited under non-marine condition•Environment of deposition: Most coals are deposited under non-marine condition
•Primary (Organic) Matter: Most coals are remnants of terrestrial higher plants
while kerogen is dominated by phytoplankton and bacteria.
•Coal as a rock, is a compact, stratified and metamorphosed plant remains with
subordinate amount of inorganic materials. These plant remains undergo a
sequence of physical, biochemical and chemical changes, which result in a series
of coal of increasing rank
•Organic materials are microscopically identifiable, they are termed macerals and
are similar to kerogen, the main precursor material of petroleum compounds.

4. COALIFICATIONCOALIFICATION
•This is a process that results in the production of coals of different
ranks ranging from peat to anthracite.
•Coalification is subdivided into;
•Biochemical phase: This involves the activities of micro organisms
such as bacteria and fungi on the organic matter
•Geochemical phase: This involves no activity of microbes to
subsequent increase in temperature and pressure through burial which
leads to further coalification increase.leads to further coalification increase.
•The general parameters used in determining the rank/series of coal;
•Moisture
•Volatile content General Parameter
•Reflectance
•Carbon Content
•Hydrogen Content Chemical Parameter
•Calorific value

5. Figure 1: Coalification, Kentuckey Geological Survey, U.S.A. 2009

6. PEAT LIGNITE BITUMINOUS ANTHRACITE
MOISTURE CONTENT DECREASES
COLOUR CHANGES (BROWN TO BLACK)
VOLATILE MATTER CONTENT DECREASES
CARBON CONTENT INCREASES
CALORIFICVALUE INCREASES
HARDNESS INCREASES

7. COAL PETROGRAPHYCOAL PETROGRAPHY
Microscopic (Petrographic) study of visible features of coal is
the basis of coal petrography. Polished coal specimens are
examined in reflected light. The petrographic components are
called Macerals.
The three groups of macerals are:
•Vitrinite/Huminite (Appears Grey)
•Liptinite/Exinite (Appears Dark)
•Inertinite (Appears White)

8. MACERAL GROUP MACERAL COMPOSED/DERIVED
FROM
VITRINITE Collinite Humic gels
Tellinite Wood, bark and cuticle
tissue
LIPTINITE/EXINITE Sporinite Spores
Cutinite Leaf Cuticles
Resinite Resin bodies and waxes
Table 1: Maceral Group, Macerals and Origins
Resinite Resin bodies and waxes
Alganite Algal remains
INTERTINITE Micrinite Unspecified detrirtal
matter <10µm
Macrinite Unspecified detrital
matter 10µm - 100µm
Semifusinite and Fusinite Carbonized wood tissue
Sclerotinite Fungal sclerotia and
mycelia

9. Table 2: Maceral Group, Subgroup and Type

10. Figure 2: Coal macerals in thin section, Kentuckey Geological Survey, U.S.A. 2009

11. Figure 3: Evolution paths of maceral groups in coals. (After van Krevelen, 1961)

12. KEROGENKEROGEN
 As organic matter matures from biopolymers (such as lipids, lignins, e.t.c.)
to geopolymers (nitrogenous and humic complexes), the resultant effect is
the formation of kerogen
 Kerogen is hence the insoluble organic matter in sedimentary rocks, the
soluble constituent is known as bitumen.
 Kerogens in sedimentary rocks (source rocks) can be examined optically
or chemically
 The optical analysis deals with viewing prepared polished sections of the
sample of rock under reflected light microscopy to reveal thesample of rock under reflected light microscopy to reveal the
microscopically proven constituents contained in the rock.
 On the basis of primary source material, there are three types of kerogen;
 Type I known as Liptinite
 Type II known as Exitinite
 Type III known as Vitrinite
However, Type IV is also known but it’s of no significance. It is
associated with coal and organic matter that has been greatly oxidised. It is
called Inertinite

13. KEROGEN
TYPE I (LIPTINITE)
Sourced from algal
lipids and bacteria
activities.
Contains high
concentration of alkanes
and fatty acids
TYPE II (EXINITE)
An admixture of
marine material and
terrestrial material.
Has more aromatic
compounds, with ester
bonds and sulfur
TYPE III (VITRINITE)
Main source of organic
matter are terrestrial plants
and rich in lignin
Abundant in continental
environment
Abundant in lacustrine
deposits
Characterize by high
H:C atomic ratio and low
O:C atomic ratio
Has HI (>300) and OI
(<50)
Best source for oil-prone
maturation and very rare
Derived from marine
organic matter
Characterize by
relatively low H:C
atomic ratio and
relatively high O:C
atomic ratio
Has HI (200-300) and
OI (50-100)
Good oil and gas
prone kerogen
 characterize by low H:C
atomic ratio and high O:C
ratio
Has HI (<200) and OI
(>100)
Less favourable for oil
generation , provide a
source rock for gas

14. Figure 4: Evolution paths of major kerogen types. (After van Krevelen, 1961)

15. Figure 5a: Photomicrograph showing Type I kerogen assemblage (Redfern, 2010)Figure 5a: Photomicrograph showing Type I kerogen assemblage (Redfern, 2010)
Figure 5b: Photomicrograph showing Type II kerogen assemblage (Redfern, 2010)

16.  The rank or maturity of a sedimentary rock containing organic matter
can be determined by measuring the reflectance of finely dispersed
small huminite or vitrinite particles. This parameter allows a sediment
to be evaluated with respect to whether oil or gas generation has
taken place (Vassoevich et al.,1969; Teichmr,iller. 1971; Dow. 1977)
 Vitrinite is a very useful kerogen type because under reflected light
microscopic analysis, its measure can be compared to a standard which
IMPORTANCE OF VITRINITE IN COAL, OILAND GAS
can depict the maturity of the source rock being examined
 In the same vein, maceral vitrinite is very important in coal petrography.
Its significance is obvious through vitrinite reflectance analysis which is
the reflectance of maceral vitrinite when oil is dropped on coal and
measured against a standard as the reflected light is essentially on the
vitrinite. Hence, the reflectance can depict the coal rank.

17. PETROLEUM GENERATIONPETROLEUM GENERATION
 The physical and chemical changes which occur with increase
in temperature and pressure with burial . This indicates that
the loss of hydrogen and oxygen, resulting in the liberation of
hydrogen- and oxygen - rich carbon containing molecules
during coalification process and is determined by type of
organic matter present, temperature, and time. These
include CO2 and CH4
 Heavier molecular weight substances similar to those found in Heavier molecular weight substances similar to those found in
petroleum are also generated in coals. This is observed
between the physicochemical properties and their structural
and chemical evolution brought about by catagenesis (Durand
et al., 1977). This is thus noted between coals and Type III
kerogens.

18. Figure 6: Relationship between coals and petroleum with maturation, aapgbull.geoscienceworld.org,
2012

19. COAL AS A SOURCE ROCKCOAL AS A SOURCE ROCK
 It has been well established that coals are capable of generating and
releasing sufficient gas to form large commercial gas accumulations
(Patijn, 1964a and b; Karweil, 1956, 1969).
 It is generally accepted that coals contain total ogranic matter above 1 –
1.5% to be a viable source rock. (Brooks&Smith 1967, Bertrand 1984)
 However, depending on the amount of liptinite in coals and chainlike
molecular structures, liquid hydrocarbons can be generated from coals.
(Akande et al., 1998: Obaje et al., 1999)
Also, some submacerals of vitrinite such as resinites, cutinites and Also, some submacerals of vitrinite such as resinites, cutinites and
desmocollinite are hydrogen rich and are capable of generating and
expelling liquid hydrobarbons (Clayton 1993, Hunt 1991, Ogala 2011)
 The origin, nature and significance of micrinite maceral to oil and gas
generation have attracted much attention. Micrinite (a submaceral under
inertinite maceral group) is related to liptinite and it is believed that it
may have been generated from liptinite (Teichmueller and Wolf ,1977) .
The concentration of micrinite particles may thus offer a useful means of
trailing the process of liquid hydrocarbon generation in coals.

20. GLOBALGLOBAL OCCURRENCE OFOCCURRENCE OF COAL DERIVED OILCOAL DERIVED OIL
 Cretaceous to Paleocene coal-bearing sequences in Bass and
Gippsland , Australia (Fielding 1992, Bishop 2000)
 Eocene coal bearing sequence in the Taranaki Basin, New Zealand
(King and Thrascher 1992, Flores 2003)
 Upper Cretaceous Mamu Formation, Anambra basin,
Nigeria(Akande et al. 1998, Obaje et al. 1998, Ogala 2011)Nigeria(Akande et al. 1998, Obaje et al. 1998, Ogala 2011)

21. BASINS HAVING COAL AS A SOURCE ROCKBASINS HAVING COAL AS A SOURCE ROCK
Table 3: World wide Occurrence of Coal as a Source Rock

22. CONCLUSIONCONCLUSION
 Coal consists of mainly detritus from (higher) terrestrial plants and is
formed under non-marine condition.
 The processes that result in the production of coals of different ranks from
peat to anthracite is termed coalification. Each rank marks a reduction in
the percentage of volatiles and moisture and an increase in percentage of
carbon.
 Chemical changes in coal during its evolution through the different
rank stages can be compared with the evolution of various kerogen
types. The greatest chemical and evolutionary similarities are observedtypes. The greatest chemical and evolutionary similarities are observed
between coal and type III kerogen.
 During coalification, low molecular weight hydrocarbons, especially
CH4 and other volatile non-hydrocarbon compounds, such as CO2 and
H2O are generated. In addition heavier, nonvolatile hydrocarbons are
formed.
 Coal is generally known as a potential source rock for gas, but may
generate commercial oil accumulations, depending on the liptinite
content.