HOBDAY, DAVID, LINCOLN PATERSON, and MICHELLE SMYTH, Australian Petroleum Cooperative Research Centre, Kensington, NSW, Australia

ABSTRACT: Reservoir Characteristics of Gondwana Coal bed Methane Targets

Developing coal bed methane resources is of critical interest to several African countries that lack indigenous hydrocarbons, and is the subject of intensive appraisal in the eastern states of Australia. Southern Hemisphere coals share common characteristics that differ significantly from their Northern Hemisphere counterparts. Most Gondwana coal-forming environments were arctic or subarctic, and associated with glacial diamictite, proglacial braidplains, mixed-load fluvial systems, and lacustrine delta-plain facies. Available precipitation tended to be bound up as ice, and as a consequence peat marshes were dominated by stunted Glossopteris flora. Northern Hemisphere swamps developed under humid tropical conditions and were characterized by trees and dense undergrowth of Lepidophyta orests. As a result of differences in flora and hydrology, Gondwana peats were more oxidized before burial and the coals have higher proportions of inertinite macerals than the inertinite-rich Northern Hemisphere coals.

Gondwana coalbed methane targets differ markedly from commercial coalbed methane reservoirs of the Warrior and San Juan Basins in terms of petrography, intra-seam variability, and reservoir characteristics. Reservoir behavior is largely dependent on maceral composition, natural fracture distribution, and secondary mineralization. Fractures are best developed in vitrinitic bands, and deflect, thin, or terminate at the margins of inertinite bands. Traditional methods of well testing and stimulation have proved inappropriate in many Gondwana reservoirs. Detailed research on local geological conditions and adaptation of technology is necessary foreffective prospect targeting and optimal well completion and stimulation design.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.