COAL AND ITS RELATION TO COAL AND ITS RELATION TO OIL AND GASOIL AND GAS

GEM 688 PRESENTATION

BY

OLADELE OLUWASAYO OLUWABUNMI

OUTLINEOUTLINE INTRODUCTION

COALIFICATION

COAL PETROGRAPHY

KEROGEN

APPLICATION OF REFLECTANCE MEASUREMENT

PETROLEUM GENERATION

COAL AS A SOURCE ROCK

CONCLUSION CONCLUSION

INTRODUCTIONINTRODUCTIONBoth 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.

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

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

PEAT LIGNITE BITUMINOUS ANTHRACITE

MOISTURE CONTENT DECREASES

COLOUR CHANGES (BROWN TO BLACK)

VOLATILE MATTER CONTENT DECREASES

CARBON CONTENT INCREASES

CALORIFIC VALUE INCREASES

HARDNESS INCREASES

COAL PETROGRAPHYCOAL PETROGRAPHYMicroscopic (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)

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 detrirtalmatter <10µm

Macrinite Unspecified detritalmatter 10µm - 100µm

Semifusinite and Fusinite Carbonized wood tissue

Sclerotinite Fungal sclerotia and mycelia

Table 2: Maceral Group, Subgroup and Type

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

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

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 the sample 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

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

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

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)

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, OIL AND 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.

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.

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

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.

GLOBAL GLOBAL OCCURRENCE OF OCCURRENCE 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)

BASINS HAVING COAL AS A SOURCE ROCKBASINS HAVING COAL AS A SOURCE ROCKTable 3: World wide Occurrence of Coal as a Source Rock

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 kerogentypes. The greatest chemical and evolutionary similarities are observed types. 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 liptinitecontent.