Introduction to the formation of Coal. Generation of methane and its entrapment in coal seams.

1. Coalification
&
Methanation
Pritish Barman
B.Tech Petroleum Engineering
2012-2016
DIBRUGARH UNIVERSITY INSTITUTE OF ENGINEERING AND
TECHNOLOGY
Department of Petroleum
Engineering

2. What is Coal?
 Coal:
 A sedimentary rock that burns
 Mineralized vetegatative material deposited over a
long period of time.
 Has altered chemical composition
 Formed by increased Temp. and Pressure
 Usually bears fissures containing water and
adsorbed methane.

3. Environments of Coal formation
 Fresh-water peat lands
 Upper delta and alluvial plain swamps
 Marshes
 Aquatic environments [Fresh Water]

4. Coal Formation
Coal formation relies on three factors:
(1) initiation, maintenance, and repetition of
environments that favor large-scale accumulation
and preservation of vegetal sediment;
(2) conditions within this depositional environment
that favor biological degradation and alteration of
the vegetal sediment to peat [peatification];
(3) geochemical processes that induce chemical
coalification of the peat to higher-rank coal.”

5. Coal Formation
 Sediment burial, subsidence of peat bogs
 Completely cuts off contact with atmospheric
oxygen
 Overburden: compaction and subsidence
 Increase Pressure, Temperature

6. Coal Rank
 Coal is not homogeneous… it needs
classification.
 Describes extent of geologic change and
metamorphism since deposition as peat.
 Low Rank  High Rank parallels:
 Loss of recognizable plant remains (macerals)
 Dull  shiny luster
 Increasing hardness
 Increasing Ash content

7. Coal Rank
Lignite ~upto 70 % Carbon
Subbituminous ~ around 80% Carbon
Bituminous ~86-91% Carbon
Anthracite ~ above 92% Carbon

8. Coal Rank
Ranks of Coal
Carbon
%
Volatile
Matter
Moisture
%
Specific
Energy
Peat 60 >60 75 14.7
Lignite 71 52 30 23
Subbituminous 80 40 5 33.5
Low-rank/volatile
bituminous 91 14 1 36.4
Medium-rank/volatile
bituminous 90 22 <1 36
High-rank/volatile
bituminous 86 31 3 35.6
Semianthracite 92 8 1 36
Anthracite 95 2 2 35.2

9. Gas Generation During Coalification
Gas Generated Volume in SCF/tonne
Methane 2000-5000
Carbon Di-oxide 6000+
Wet Gas 100-1000+
Nitrogen 250-500+

10. METHANATION
 Biogenic methane
 produced by anaerobic bacteria in the early stage of
coalification
 Thermogenic methane
 mainly during coalification at temperatures of 120 –
150° C

11. METHANATION
Vegetal Matter
Biochemical
(by organism at <50°C & at 0.5-
10 m depth)
Geochemical
(by increased temperature &
pressure at >10 depth)

12. METHANATION
Biochemical
Diagenesis
(Humification)
Pit coal
(Ro max 0.2-0.3%)
Lignite coal
(very less % retained
&rest is released to the
surrounding in the form of
diagenic gas)

13. Geochemical
Catagenesis
(Bituminization,debituminization)
Sub-bituminous
Bituminous
(very small amount of methane is
released to the surrouding as the
thermoginic gas & most of the gas is
retained in the coal bed)
Metagenesis
(>150°C-200°C
Ro max >2-4%)
-Semi anthracite
-Anthracite