Enhanced Coalbed Methane Technology Introduction - … · Technology Introduction ... What is Coal?...
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Transcript of Enhanced Coalbed Methane Technology Introduction - … · Technology Introduction ... What is Coal?...
Enhanced Coalbed Methane (ECBM) Technology Introduction
Institute of Rock and Soil MechanicsChinese Academy of Sciences
Zhiming Fang
What is Coal?
A readily combustible rock containing more than
50% by weight and more than 70% by volume of
carbonaceous material formed from compaction
and induration of variously altered plant remains
similar to those in peaty deposits – Schopf (1956)
A carbonaceous substance composed of
phytogenetic materials – Spackman (1958)
A black rock that burns
What is Coalbed Methane (CBM)?
Gas generated during coalification
Gas is 85 – 99% methane (CH4)
Gas is held on coal matrix by adsorption
Structure of Coal: Dual Porosity System
面割理面割理
端割理端割理基质
裂隙
孔隙
Natural fractured coal Dual porosity model
Butt cleat
Face cleat
Matrix
Cleats
Porosity
Primary porosity Coal matrix
Secondary porosity Coal cleats
Gas Storage Mechanisms
Gas can exist in a coal seam in two ways:
Free gas within coal cleats and natural fractures
Adsorbed layer on the surface of micropores
Because the bulk porosity of the coal cleat system (i.e.
secondary porosity) is small (<5%) and initial gas saturation in
the coal cleats is typically low (<10%), most of the gas‐in‐place
in coals (>90%) is adsorbed in the coal matrix
Total gas Volume
= Free GasVolume
+ Adsorbed Gas Volume
Gas Storage Mechanisms Langmuir Isotherm
Gs=abp
1+bpwhere:
Gs = gas storage capacity, ml/g
a = Langmuir storage capacity, ml/g
b = Langmuir constant, MPa‐1
p = pressure, MPa
Typical Langmuir isotherm adsorption curve
Gas Transport Mechanisms
Controlled by
pressure gradient
Follow Darcy’s Law
Controlled by
concentration
gradient
Follow Fick’s Law
Controlled by partial
pressure
Follow Langmuir
equation
CBM Primary Production Mechanisms
Reduce cleat pressure by producing water
Methane desorbs from matrix and diffuses to cleats
Methane and water flow to wellbore
Low coal permeability (In China, the initial permeability
of 72% of coals < 1mD)
Low gas flow rate
Low gas recovery ratio
Bottleneck of CBM Primary Production
Enhanced CBM TechnologyConcept
CO2
CO2
CH4
CH4
CH4CH4
CH4CO2
To inject gas into deep unminable coalbed for enhanced recovery of coalbed methane (ECBM) recovery
Primary porosity e. i., CO2
Inert gas e. i., N2
Enhanced CBM TechnologyCO2‐ECBM Recovery Mechanisms
Injected carbon dioxide in cleats
Increases total cleat pressure
Carbon dioxide diffuses into matrix and strongly adsorbs onto coal
Reduces partial pressure of methane in cleats
Methane desorbs from matrix and diffuses to cleats
Methane and water flow to wellbore
Enhanced CBM TechnologyN2‐ECBM Recovery Mechanisms
Injected nitrogen into cleats
Increases total cleat pressure
Nitrogen diffuses into matrix and weakly adsorbs onto coal
Reduces partial pressure of methane in cleats
Methane desorbs from matrix and diffuses to cleats
Methane, nitrogen and water flow to wellbore
CO2 is stored – Greenhouse gas reduction
and at the same time the recovery of
coalbed methane is enhanced ‐
Why CO2‐ECBM attract more attention?
Schematic of CO2-ECBM
YubariRecopol
Qinshui Basin
Central Appalachian
MGSC-ECBM
PCOR Lignite CSEMP
Fenn
SWP San Juan
Allison Unit
Black Warrior
YubariRecopol
Qinshui Basin
Central Appalachian
MGSC-ECBM
PCOR Lignite CSEMP
Fenn
SWP San Juan
Allison Unit
Black Warrior
Distribution of pilot test in the world
USA Japan UN Canada+China
CO2‐ECBM Pilot Test in The world
However, pure CO2 as a displace gas has following problems:
1. Making the coal swell and therefore reducing its
permeability; In China, the initial permeability of 72% of
coals < 1mD.
2. It is difficult to identify “unminable” coal at present; The
ECBM projects may conflict with mining.
Challenges of CO2‐ECBM in China
Gas mixture ECBM
CO2
CO2
CH4
CH4
CH4CH4
CH4CO2
N2/CO2
CO2
CO2
CH4
CH4
CH4CH4
CH4CO2
N2/CO2Gas Mixture
Mechanisms
The concept of G‐ECBM technology is to inject gas mixture, consisting mainly of N2 and CO2, into the coalbed through the injection wells to displace the methane from the coal and drive it to the production wells.
G‐ECBM: Features
Balancing the preferential sorption role of CO2 and
permeability‐enhancing role of N2.
Suitable for low‐permeability and minable coals, help to
control gas outburst and enhance methane recovery,
therefore, attract the interest of enterprises.
Lowering, even eliminating the cost of gas purification.
Fat coal
620m deep tunnel
Initial permeability is 4μD
3 test wells+220 existing production wells
Pilot Test in Pingdingshan Coal Mine
Overview
of the Test
Results of pilot test
Flow
rate
of m
etha
ne(m
3 /hr)
Flow
rate
of a
ir (m
3 /hr)
0
0.5
1
1.5
2
11月5日
11月15日
11月25日
12月5日
12月15日
12月25日
1月4日
1月14日
1月24日
2月3日
日期
CH
4流量
(m3 /h
r)
0246810
注气流量(
m3 /h
r)
开始注气
注气流量
CH4流量
2.0
1.5
1.0
0.5
0
10
8
6
4
2
0
Air injection
air
Flow
rate
of a
ir (m
3 /hr)
DateNov.5 Nov.15 Nov.25 Dec.5 Dec.15 Dec.25 Jan.4 Jan.14 Jan.24 Feb.3
0
0.5
1.0
1.5
2.0
开始注气Fl
ow ra
te o
f met
hane
(m3 /h
r)Air injection
Flow
rate
of m
etha
ne(m
3 /hr)
0
0.5
1.0
1.5
2.0
Flow
rate
of m
etha
ne(m
3 /hr)
Air injection well 3
well 2
well 1Flow
rate of m
etha
ne (m
3 /hr)
Date
Air injection
Airinjection
Air injection
Air
CH4
CH4
CH4
Comparing with 220 conventional production wells, the average single‐well flow rate and the average concentration of the CH4 of the test wells increased by 4.7 times and 1.7 times, respectively
Comparing with 220 conventional production wells, the average single‐well flow rate and the average concentration of the CH4 of the test wells increased by 4.7 times and 1.7 times, respectively
Pilot test summary
1# hole2# hole3# hole
Boring holes nearby(220 by traditional method)
Comparation ECBMwith traditional method
The number of ring hole
60.13
0.63
0.86 23.543.4
Average flow rateof CH4(m
3/hr)Average concentration
of CH4(%)
5.7 2.7
8.60.422