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Coalbed Methane potential of the anthracite Groundhog/Klappan Coalfield Northern Bowser Basin Barry Ryan New Ventures Branch Ministry of Energy and Mines BC Email barry.ryan@gems4.gov.bc.ca. Lost Ridge Klappan area. OR. CBM in the green blob Fantasy or Future.

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Presentation Transcript
slide1

Coalbed Methane potential of the anthracite Groundhog/Klappan Coalfield

Northern Bowser Basin

Barry Ryan

New Ventures Branch

Ministry of Energy and Mines BC

Emailbarry.ryan@gems4.gov.bc.ca

Lost Ridge Klappan area

slide2

OR

CBM in the

green blob

Fantasy or Future

slide3

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

slide4

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

slide5

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

slide6

Drilling and trenching in the coalfield is concentrated in the north Klappan area and in the south Groundhog area

Klappan

Groundhog

slide7

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

Klappan east

Klappan west

McEvoy Flats

Biernes synclinorium

Panorama

slide8

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

slide9

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

slide10

Metres

There is good data density in the northern Klappan area where the seam stratigraphy is established

slide11

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

slide12

Vitrinite reflectance data from the coal section provides an estimate of the rank through the coal bearing section (sections?)

Biernes Synclinorium

4

3.5

4.5

5

Resource area

3

4

5

slide13

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

slide15

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

slide17

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

slide18

Anthracite is very good at adsorbing methane

a single isotherm is available for the Groundhog/Klappan coalfield

slide19

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

slide20

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

slide22

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

slide23

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
slide24

Olszewski (1992) developed the Langmuir Rank Equation . It provides a very rough estimate of anthracite isotherms at different temperatures

slide25

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
slide26

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

slide27

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

slide28

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

slide29

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

slide30

Anthracite is hard and will fracture but may not produce as much fine coal as medium volatile coals which are much more friable

Klappan

slide31

Evidence from crushed screened sample indicates low percent of super fine material generated by anthracite

slide32

Conclusions

There 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