The gas adsorption capacity of the coals varies regionally with depth of burial (pressure), coal rank, and ash content. The highest adsorption capacity at reservoir pressure and temperature, approaches 4001 scf/t, but most coals have values between 260 and 320 scf/t. The gas content of the coals, as measured by desorption, ranges from 230 to 350 scf/t and averages 310 scf/t. Most of the coals are saturated with gas within the accuracy of the analyses. Notable exceptions occur adjacent to the Saskatchewan border where the lower rank coals may be markedly under saturated. The amount of methane in solution (calculated) at a reservoir pressure of ≈ 1000 psig (6.9 MPa) is calculated to be between 7 and 10 scf/t (≈ 3% of total gas).
Currently, Mannville coal gas production is limited to an area in central Alberta of about 2200 km2 (850 miles2). Outside the producing fairway, sustained commercial production has not been achieved due to low permeability. In the producing and prospective fairway, the net thickness of the coal within ± 20 m of the main coal seam, varies from 0 to 10.8 m and averages 5.1 m. Here the thickest coal seam ranges up to 4.7 m thick and averages 1.9 m.
Due to limited gas content data from core for all seams and wells, a protocol was developed to extrapolate existing core data to non-cored seams and wells through petrophysical logs. The protocol takes into consideration the correlation between gas and ash content and the maturity of the coals. The total coal gas resource density in the current area of production and prospective areas determined by applying this protocol for the average well has a low estimate of 5.4 BCF/mi2(2) (m3/km2), a median estimate of 5.9 BCF/mi2, and a high estimate of 6.1 BCF/mi2.