Petrography of Ardley Coals, Alberta - Implications for Coalbed Methane Potential

This report describes chemical and petrological characteristics of coal seams from the Ardley Coal Zone, Scollard Formation, and Alberta and evaluates their coalbed methane (CBM) potential. The seams were sampled at mine sites west of Edmonton (Genesee, Highvale, Whitewood) and from outcrop sections in the Red Deer Valley, east of Red Deer. The seams were sampled 1) by full seam channel samples, which were subsequently analyzed by proximate analysis, determination of sulphur content, vitrinite reflectance and maceral analysis; and 2) by many lithotype samples from seam base to seam top to determine in-seam variations in petrography composition

The results indicate that all coals are subbituminous in rank and will not have generated thermally derived gas. However, biogenic gas may have been generated by interaction with circulating ground water. Cumulative coal thickness at the locations studied is between 5 and 10 m, with individual seams having a thickness in excess of 3 m. These factors make the Ardley Coal Zone an exploration target in areas, which increased coal rank at depth, may have generated significant amounts of thermogenic gas. Also favourable for CBM exploration are the relatively low ash yields (11-21 wt. %) and sulphur contents (0.15-0.48 wt. %) in seams greater than 1 m in thickness.

The seams show significant differences in petrographic composition, with the highest vitrinite contents associated with the base of the coal zone (No. 6 seam at Highvale and Whitewood and No. 3 seam at Genesee). Predominant lithotypes in most seams are banded dull and dull, although some coals are characterized by predominance of banded coal and banded bright and bright lithotypes.

The comprehensive petrographic dataset on the Ardley Coal Zone presented in this report has demonstrated that

1) There exist significant compositional differences between the various seams; and

2) There exist significant in-seam compositional variations, both on the macroscopic (lithotype) and microscopic (maceral) level.

Based on previous studies, it is suggested that the brighter seams of the Ardley Coal Zone and the seams with the highest vitrinite contents will have the highest potential for gas generation and gas storage.