Coal-bearing strata as source rocks — a global overview

Compilation of a global source rock database has shown that coal-bearing sequences are significant oil generators only in very specific and relatively uncommon geological settings. Coals and associated carbonaceous shales are thought to be the primary oil-prone source facies in Australasia and an important secondary source facies in Southeast Asia. In other regions of the world, there is, however, no evidence that they have expelled major quantities of oil. In terms of their contribution to the worldrss petroleum reserves, coal measures are the origin of relatively minor proportions of oil, but of significant amounts of gas. Coal sequences that are believed to have expelled significant amounts of liquid hydrocarbons seem to be restricted to two palaeoclimatic and palaeobotanical ‘fairways’. 1. Tertiary angiosperm assemblages within 20° of the palaeo-equator. 2. Late Jurassic-Eocene gymnosperm assemblages formed on the Australian and associated plates. The reasons for this are not well understood. Multidisciplinary research work is recommended to compare these oil-prone coals with the much greater volumes of apparently gas-prone coals deposited outside these regions.