Alberta Geological Survey created a coal and coalbed methane (CBM) database to capture and manage CBM data. The database compiles different sources and contains information on 7923 wells (15,200 formation picks, 37,357 coal picks, 495 coal analyses and 363 vitrinite reflectance measurements).
From this parent dataset, individual coal zone was evaluated. This record describes the McKay Coal Zone's calculated gas in place in BCF/Section.
The gas-in-place resource for the McKay coal zone in billion cubic feet/Dominion Land Survey section (bcf/section), dry, ash-free basis (daf) was calculated as follows:
Step 1: Calculate gas content on a dry, ash-free basis (daf) for the coal zone using the methodology described in: GRI Coalbed Methane Guides V.2. "Determining gas content & gas-in-place analysis." Gas Research Institute 1998, GRI-98/0365.2 (CD-ROM)
1) For depth to top > 200 m: gas concentration (cc/g, daf)= Lv x (depth x grad)/(depth x grad)+(Lp x 0.70)
and
2) For depth to top < 200 m: gas concentration (cc/g, daf)= Lv x (depth x grad)/(depth x grad)+(Lp x 0.40)
where Lv is Langmuir volume (cc/g, daf) and Lp is Langmuir pressure (Mpa), both obtained from isotherm analyses; depth is depth to top of coal zone (m); grad is pressure gradient (Mpa); daf is dry, ash-free basis; and 0.70 and 0.40 are gas saturation values. Saturation percent determined by comparing gas adsorption capacity (Langmuir parameters) to measured desorbed gas content.
Note: Langmuir volume and pressure were determined by laboratory analysis on coal samples from the coal zone according to Langmuir, I.: "The Adsorption of Gases on Plane Surfaces of Glass, Mica, and Platinum," Journal of the American Chemical Society, Vol. 40 (1918) pp. 1,361-1,403.
Step 2: Calculate gas-in-place using the calculated gas content for the coal zone (cc/gm daf)
1) The gas resource in bcf/section (dry, ash-free basis) is given by
Gas resource (daf) = gas content (cc/g, daf) x Pure coal density (g/cc, daf) x net coal thickness (cm) x (9.146 x 10-4)
where Pure coal density = 0.905 + 1.593Ro – 2.886Ro2 + 2.392Ro3 – 0.913Ro4 + 0.133Ro5
Ro is vitrinite reflectance; 9.146 x 10-4 is the constant for conversion from (cm3/cm2) to bcf/section; and daf is dry, ash-free basis.
This coal zone falls within the high-volatile bituminous range, represented by the reflectance range of 0.50% to 0.65%. Pure coal density was calculated using modified equations of others, as reported by Scott, A.R., Zhou, N. and Levine, J.R. 1995. "A Modified Approach to Estimating Coal and Coal Gas Resources: Example from the Sand Wash Basin, Colorado". AAPG Bulletin v.79, no.9, p1320-1336., which indicated a pure coal density of 1.23 g/cc for this range of coal ranks.
Gas-in-place resource results were gridded and contoured in Viewlog using its Simple Kriging method. Contour lines were exported from Viewlog as a DXF file. This was imported into ArcGIS and written out as a shapefile.