Coal and its Relation to Oil and Gas

Abstract

When discussing the formation and occurrence of petroleum, it is necessary to include a brief review on relevant aspects of coal formation. Both petroleum and coal originate predominantly from organisms of the plant kingdom and both are subjected to the same geological processes of bacterial action, burial, compaction, and geothermal heating that constitute diagenesis and catagenesis. There are, however, also some essential differences between the modes of coal and petroleum formation. Basically, these differences center around the fact that coal is found at its site of deposition as a solid and relatively pure massive organic substance, whereas petroleum is liquid and migrates readily from its place of origin into porous reservoir rocks. Kerogen is the main precursor material of petroleum compounds. It is finely dispersed and intimately mixed with the mineral matrix in petroleum source beds. Most coals are remnants of terrestrial higher plants, whereas the kerogen of petroleum source beds is generally dominated by aquatic lower plants and bacteria. Most acknowledged petroleum source beds were deposited in marine environments and most coals formed under nonmarine or paralic conditions.