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Lost Ridge Klappan area
Coalbed Methane potential of the anthracite Groundhog/Klappan
CoalfieldNorthern Bowser Basin
Barry Ryan
New Ventures Branch
Ministry of Energy and Mines BC
Email [email protected]
CBM in the
green blob
Fantasy or Future
OR
This talk will discuss the anthracite
and
coalbed methane resource in the northern Bowser Basin
This is the Groundhog/Klappan coalfield
which covers about 5000 square kilometres
or 10% of the area of the Bowser Basin
Coal prospects are scattered through the Bowser basin
Most are found in an area of 5000 KM2 in the northern part of the basin
This area is referred to as the Groundhog coalfield
or more recently
the Groundhog coalfield in the south and the Klappan
coalfield in the north
I have combined the names for the moment
Coal prospects identified by coal assessment reports (postage stamps) are concentrated in the coalfield but are also scattered through other parts of the Bowser Basin
Groundhog-Klappan
Drilling and trenching in the coalfield is concentrated in the north Klappan area and in the south Groundhog areaKlappan
Groundhog
Klappan eastKlappan west
Biernes synclinorium
Panorama
McEvoy Flats
The Klappan/Groundhog coalfield forms an area roughtly defined by the trace of the Biernes synclinorium
and areas of coal bearing rocks that have been prospected over the years
Here the coalfield is divided into a number of sub resource areas for convenience
A CBM resource assessment requires an estimation of
1/ in place coal tonnage in a prospective depth window
And
2/ An estimation of the in place gas content
Data was collected from over 142 drill holes and numerous trenches to estimate
the amount of coal in the section in the resource areas
Data can be displayed as simple depth x coal thickness x ash content
strip logs or manipulated in other
ways
hole 82010
20
40
60
80
100
120
140
0 20 40 60
K
G
Ash%
82020
20
40
60
80
100
120
140
160
0 20 40 60
G
Ash%8203
0
20
40
60
80
100
120
140
160
180
200
0 20 40 60
K
G
Ash%
There is good data density in the northern Klappan area where the seam stratigraphy is established
Seam thick ashQ 2.7 58.46
PH 2.0 39.41P 1.7 34.47O 1.6
NU 0.9N 2.6 38.61
M/N 2.1M 2.2 41.36L 2.7 40.38
K/L 2.2 45.04K 2.3 34.64J 3.4 31.49I 2.7 25.12
H/I 2.5 39.12H 3.0 38.53
GU 2.1 51.95GL 2.1G 2.3 44.99F 2.1 39.98E 2.5 26.85D 3.8 46.04C 1.9 33.69B 2.3A 2.2
Metres
Vitrinite reflectance data exists for coal samples from numerous areas
It is difficult to define the stratigraphic position of the samples but they do when contoured
provide an estimate of the rank of the coal in the coalfield
Most values indicate that the coal is anthracite
Biernes Synclinorium
Resource area
Vitrinite reflectance data from the coal section provides an estimate of the rank through the coal bearing section (sections?)
4.5
5
3
4 3.5
5
4
CBM Resource
Coal tonnage times estimated gas content
provides an estimate of potential CBM in place resource
This number indicates the size of the box in which a reserve might be found
it provides almost no indication of its size or where it might be found
Resource box
elusive and ill defined reserve box
Coal and CBM potential resource Groundhog/Klappan Areaaverage ash 30assumed specific gravity 1.5conversion cubic metres to cubic feet 35.31assumed average gas content as cc/gm 5
Sub
are
as
area
aver
age
rank
R
max
%
cum
ulat
ive
coal
m
etre
s
Cum
ulat
ive
coal
bi
llio
n to
nnes
cum
ulat
ive
gas
as
bcf
McEvoy flats 577 4.39 16.1 13.9 2460Panorama 275 3.05 9.1 3.8 664
Beirnes Syn 538 2.83 14 11.3 1994Klappan west 374 3.67 18.9 10.6 1871Klappan east 210 3.62 26.25 8.3 1459
SumResource area 1974
total cumulative coal 48total gas as tcf 8
The cooking required to make anthracite
expels most previously adsorbed methane
For anthracite to have adsorbed gas at the depth (=pressure and temperature conditions) sampled
it must re adsorb previously expelled
thermogenic methane
or
generate biogenic methane
DURING COALIFICATION COAL
GENERATES MORE METHANE
THAN IT CAN RETAIN
THE EXCESS IS EXPELLED
INTO SURROUNDING ROCKS
DURING UPLIFT COALS
ABILITY TO RETAIN GAS INCREASES
IF IT IS TO REACH
SATURATION IT MUST
GENERATE BIOGENIC METHANE
OR RE ADSORB METHANE
FROM SURROUNDING ROCKS
0
1000
2000
3000
4000
5000
6000
7000
0 5 10 15 20 25
gas cc/g or temp ºC/10d
epth
met
res
progressive rank adsorption curveduring coalification
MVBHVB
LVB
temperature gradient
arrows=makeup gas for saturation at 1400 m
LVB
FINDFIND
FIND
black dashed lines adsorption curves during uplift
There is no way of estimating the gas content of Groundhog/Klappan anthracites but data do exist for Chinese anthracites
The average value of 5 cc/gm appears to be conservative
Anthracite is very good at adsorbing methane
a single isotherm is available for the Groundhog/Klappan coalfield
0
5
10
15
20
25
30
35
40
0 500 1000 1500 2000 2500
metres
gg/g
m
22'C isotherm
eddy curve
Anthracite adsorption isotherm
However
Anthracite if it has it
doesn’t want to give it back
Turning a resource into a reserve
might be difficult
So here are some ideas
The time it takes gas to diffuse through the coal matrix to the cleats where flow takes over is controlled by
particle size
Rank
Petrography
At higher ranks coal structure becomes more organized and aromatic rings develop and cluster
This process accelerates in the rank window 1.8% to 2%
Pores within the anthracite are flattened and sealed by aromatic ring clusters with low diffusivity.
The density of anthracite decreases and the surface area available for adsorption increases but diffusivity is low
From Bustin et al, 1983
Production history changes based on changes in diffusivity (modelling Black Warrior Basin) When diffusivity is low it becomes the rate controlling process from Sawyer et al 1987
1.2 days for 66.3% gas desorption
11.6 days
115.7 days
I have not had time to locate much information on the relative diffusivities of anthracites versus medium volatile coals but
Some points to develop
Diffusivity is temperature dependent
Diffusivity is particle size dependent
Anthracites are hard have low diffusivity and may respond like very organic rich shales
0
5
10
15
20
25
30
35
40
0 500 1000 1500 2000 2500
metres
gg/g
m 20'C406080
22'C adsorption
eddy curve
Some Chinese data
actual adsorption trend during uplift
Anthracite data temperature data from Olszewski 1992
Olszewski (1992) developed the Langmuir Rank Equation . It provides a very rough estimate of anthracite isotherms at different temperatures
Plot illustrates that based on an assumed geothermal gradient maximum adsorption occurs at about 500 metres
ie
shallow depth cheap drilling
low pressure easy to predict geology
hopefully good permeability
In the depth range for biogenic methane generation
Plot also indicates some Chinese anthracite data
Eddy anthracite curve
Isotherm curve for Groundhog/Klappan anthracite
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 5 10 15 20 25
methane concentration cc/gm
dif
fusi
vity
50 'C
25 'C
0 'C
50 'C
25 'C
0 'C
medium volatile
Anthracite
10^
3 *
D^
(1/2
) /
ro *
(s^
(-1/
2) )
The diffusivity of anthracite appears to be less than half that of
medium volatile coals
However
An increase in 50’C increases diffusivity by a factor of 7
Nandi and Walker 1974
0
5
10
15
20
25
30
35
40
0 100 200 300 400 500 600 700 800 900 1000
depth in metres
cc/g
m
80'C
20'C
gas released at constant pressure by increasing temperature
Because adsorption decreases as temperature increases
If temperature increases from 20 to 80’C then at a pressure equivalent to 110 metres 15 cc/g of gas will be released and diffusivity will be much better
Maybe -- think of anthracite as heavy oil It may be possible to make use of temperature to improve diffusivity and anthracite hardness to produce extensive
hydro fracing with minimal
de pressuring of seam
hot water
hot or heated waterre injected
gas and water returned to surface
deep heated aquifer
Coal seam
There is some data to indicate that deformation improves the diffusivity of anthracites.
The Groundhog/Klappan area is certainly deformed
Data from Wales indicates a relationship shearing of anthracites and diffusivity
Indications of 7 times increase based on sampling in different locations
Data from Harris et al 1996
0
2
4
6
8
10
12
14
16
18
20
0 0.5 1 1.5 2
Hand Drill Penetrometer cm/sec
T f
or
63
% g
as
in m
inu
tes
Anthracite is hard and will fracture but may not produce as much fine coal as medium volatile coals which are much more friable
Klappan
Evidence from crushed screened sample indicates low percent of super fine material generated by anthracite
0
5
10
15
20
25
30
0.01 0.1 1 10 100
mid size in millimetres
wei
ght
per
cen
t
medium vol HGI>80
anthracite HGI<40
high vol coal HGI about 45
ConclusionsThere is a lot of anthracite in the G/K coalfield
There could be a lot of CBM in the G/K coalfield
Any oil and gas development will provide infrastructure
Is anthracite a very organic rich shale not a problem coal ??
Is temperature the key to over coming diffusivity problems ??
Is deformation a good thing - it improves anthracite diffusivity ??
Anthracite generates less fine material than lower rank coals ??
The Groundhog/Klappan coalfield
Are perceived problems opportunities for those with vision