Greenhouse Emissions from Western Canadian Metallurgical Surface Coal Mines: Top Down and Bottom Up Measurement and Potential for Abatement

To establish verifiable  mine scale green house gas emission factors and evaluate the potential for emissions abatement from surface coal mines in Canada  we have undertaken a multi-mine study to predict the residual gas in place in the coal and coal measures that will become fugitive as result of mining operations as well as quantify the actual emissions during different phase of mine operations using both top down and bottoms up methodologies.

Top down satellite and airborne measurements of the study mine sites show no measurable fugitive methane with one exception.  At the same time and in the same mines when satellite and airborne data yield no detectable emissions, our bottoms up measurements using static and dynamic flux chambers and our mobile laboratory find significant emissions. The static and dynamic chambers which measure emission directly quantify a large degree of variability in both methane and carbon dioxide emissions which reflects the lithology with bright banded ash poor coals yielded the highest emissions and organic poor sandstones the lowest (or no) emissions.  . The emissions were highest through recently drilled blast holes that intersect coal and lowest in rock dumps. Background emissions in areas where the coal measures are yet to be disturbed by mining range from below detection limit to several ppb above background for methane and 10s of ppm for carbon dioxide.  Where background values are highest appear to correspond to liniments which are likely faults which are common in the mines.  The emissions data also varies a smaller scale diurnally, with atmospheric pressure and seasonally with the lowest concentration at night, with low pressure and in winter.

 Measurement of fugitive gases in air (plumes) were measured on multi transacts in several mines. The  largest plumes with the highest fugitive methane content were measured following blasting operations. Methane and carbon dioxide emissions were also tracked through the mining operations  from excavation, crushing, washing and blending.  Overall the transacts show high temporal variability  in fugitive GHG emissions that in large part reflect mining operations.

 To determine the practicality of pre- or during mining drainage of the residual gas by drilling directional boreholes will reduce emissions, we have reservoir modelled the coal measures.   At the shallow depths of surface mines and hence their lower reservoir pressure, pre-draining significant quantities of gas is challenging.  Reservoir models however, show that through strategic placement of boreholes, significant gas can be drained.