An Introduction to Migration and Accumulation of Oil and Gas

Petroleum accumulations are generally found in relatively coarse-grained porous and permeable rocks that contain little or no insoluble organic matter. It is highly improbable that the huge quantities of petroleum found in these rocks could have originated in them from solid organic matter of which now no trace remains. Rather, as discussed in previous sections, it appears that fluid petroleum compounds are generated in appreciable quantities only through geothermal action on high molecular weight organic kerogen usually found in abundance only in fine-grained sedimentary rocks and that usually some insoluble organic residue remains in the rock at least through the oil-generating stage. Hence, it can be concluded that the place of origin of oil and gas is normally not identical with the locations where it is found in economically producible conditions, and that it has had to migrate to its present reservoirs from its place of origin. This migration of petroleum, and the subsequent formation of commercial accumulations, will be discussed in this part of the book.