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 barry.ryan@gems4.gov.bc.ca

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