Lost Ridge Klappan area Coalbed Methane potential of the anthracite Groundhog/Klappan Coalfield Northern Bowser Basin Barry Ryan New Ventures Branch Ministry of Energy and Mines BC

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 KM 2 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

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

Klappan east Klappan 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

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

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

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

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

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 days for 66.3% gas desorption 11.6 days 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

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

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

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

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

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

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