This document discusses coalbed methane (CBM) formation and production. CBM is formed during coalification from either chemical reactions or bacterial action. It is stored in the micropores and macropores (cleats) of coal. CBM production involves three phases - an initial dewatering phase to remove water from the cleats, a stable production phase where gas production increases as water production decreases, and a declining phase where production declines over time. Key factors that influence CBM production are total gas content, coal's sorption capacity, permeability, and diffusion properties.

1. Mohammad Asif ( BT09MIN008)
Advisor: Dr. Mallikarjun Rao

2.  Introduction
 CBM formation
 Physical Structure of Coal
 CBM production controls
 CBM production process

3.  Coalbed methane is an unconventional source of
energy that is formed during the process of
coalification, remains in coal in the form of
adsorbed gas
 Along with the methane, small amounts of other
hydrocarbon and non-hydrocarbon gases formed
during the process
 Coals have an immense amount of surface area
and can hold enormous quantities of methane
 Coal can store on the order of six to seven times
more gas than the equivalent volume of rock in a
conventional gas reservoir

4.  CBM in coal is a result of chemical and
physical processes
 CBM is generated either through chemical
reactions or bacterial action
 Chemical action occurs over time as heat and
pressure are applied to coal in a sedimentary
basin, referred to as thermogenic methane
 Bacteria obtain nutrition from coal, and
produce methane as a by-product, is referred
to as biogenic methane

5. C
O
A
L
CHEMICAL
REACTION
BACTERIAL
ACTION
THERMOGENIC
METHANE
BIOGENIC
METHANE

6.  Coal has a dual porosity structure
◦ Micropores < 2nm
◦ Macropores > 50nm
 Macropores are natural fracture that exists
perpendicular bedding plane also called
cleats
◦ Face cleats
◦ Butt cleats
 Micropores are exist between cleats which are
also called coal matrix

9.  Movement of methane in coal occurs at three
phase:
◦ phase 1: Desorption of methane form internal
surface of coal
◦ phase 2 : Movement of desorbed methane from
coal matrix to cleats through diffusion following
Fick’s 2nd law of diffusion
◦ phase 3 : Transportation of methane from cleats to
production well following Darcy’s law of fluid
through porous media

10. Desorption from
coal Surface
Diffusion from
matrix to cleats
Movement within
the cleats

11.  Total gas-in-place in coal reservoir
 Methane sorption capacity of coal
 Diffusion in coal
 Permeability of coal

12.  Gas in place is
measured by taking
core from drilling ,
placing it in a canister
, and measuring the
gas it desorbed

13.  Adsorption capacity of coal is defined as the
volume of gas adsorbed per unit mass of coal
usually expressed in SCF (standard cubic feet,
the volume at standard pressure and
temperature conditions) gas/ton of coaI
 Important factors that affect methane
sorption capacity of coal are
◦ Pressure
◦ Temperature
◦ Rank
◦ Ash and moisture content

14.  The volume of gas adsorbed increases with
increasing pressure
 The volume of adsorbed methane decreases
with increasing in temperature
 Methane sorption capacity of coal increases
with increase in coal rank from peat to
Anthracite
 As some of the pores in coal pre occupied
water (moisture), methane sorption capacity
of coal decreases with increase in moisture
and ash content

20.  Diffusion in coal is governed by Fick’s 2nd Law
 Sorption time is time taken by drill cuttings
to desorb 63% of total gas in place
 It is very important factor in determining the
gas production rate in high permeability
reservoir
 The relationship between sorption time and
diffusion coefficient is expressed as

21.  It is the most important factor in determining the
methane production rate from a coal seam
 It is governed by Darcy’s law
 It is depend on the cleat spacing and effective
reservoir pressure
 Effective pressure defined as the difference
between confining pressure and pore pressure
 Increase/decrease in the permeability with gas
depletion depends on shrinkage/swelling
characteristics of coal

22.  Coalbed methane production passes through
three phases during the life-time of the
reservoir
 Dewatering phase
 Stable production phase
 Declining phase

24.  During this phase CBM wells experiment a
constant water production with a very low or
negligible gas production
 Initially, most CBM wells are naturally water
saturated because water liberation occurs
during the coalification process
 The water is occupying the principal cleat
network and there is the need of removing
the water from the major fractures system in
order to produce gas

25.  The number of days of this dewatering
process and the amount of produced water
can vary widely
 They are very difficult to estimate and their
influence in the economics is very hard to
predict
 The major physical properties that affect the
efficiency of the dewatering process are:
◦ Permeability,
◦ Adsorbed gas content,
◦ Relative permeability

26.  Phase II is described by a dramatically
decrease in the water production and
increase of the gas production rate
 The water relative permeability decrease and
the gas relative permeability increase
 The gas production has stabilized and starts
to experiment a typical decline trend

27.  During phase III, the well is considered to be
dewatered, so the water production is in the
low level or negligible.
 The water and gas relative permeability do
not change extensively
 The steady state exists for the rest of
producing life
 The limit between phase II and III is
determined by the peak gas rate is reached

29.  Visit one of CBM production sites
 Study the CBM production process in field
 Study the gas and water production
characteristics

30.  CBM in India
http://www.fekete.com/software/cbm/med
ia/webhelp/Index.htm#c-te-production.
htm
 Coal Bed methane(CBM),
http://www.nuenergygas.com/about-cbm/
 Coal Bed Methane(black coal , green
future….),
http://www.sgtk.ch/rkuendig/dokumente/
CBM.pdf

31.  Estimating methane content of bituminous
coalbeds from adsorption data,
http://www.cdc.gov/niosh/mining/UserFile
s/works/pdfs/ri8245.pdf
 Rudy E. Rogers, Coalbed methane : Principles
and practices, Prentice Hall, 1994