The origin and accumulation of oil still remain among the many unsettled problems of the geology of petroleum. The theory that oil source material is sparsely and widely disseminated organic matter in shales and limestones, and that free oil migrates long distances to its final trap, fails to satisfy conditions of most oil pools.
It is suggested that oil source material is accumulations of rich organic matter deposited in restricted areas near to, indigenous to, or in contact with, the reservoir and trap of the present oil pools. It is probable that source material is more closely associated with local conditions of sedimentation and environment than has been generally considered. The location of these deposits of rich organic matter is probably controlled by local favorable conditions of sedimentation on the floor of the epicontinental sea, by local favorable climatic conditions, by routes of travel of sea fife, by food supply, and by shallow warm water, all these conditions being favorable for the growth, propagation, and accumulation of organic matter. The source material is probably minute organisms of a low order and perhaps plant spores, all of which left few, if any, fossil remains. Several types of oil occurrences are cited in support of the theory that restricted accumulation s of rich organic matter are the source of petroleum, which is in conflict with the theory that widely disseminated organic matter in lean shales and limestones is the source of oil, and with the theory that free oil migrates long distances from its source to the trap.
Figures & Tables
The AAPG volumes of Structure of Typical American Oil Fields preceed this book, which was written as a sequel to those, and at first conceived as a third volume of the earlier work. This book is designed to review, modify and, if possible, clarify ideas with regard to the fundamental concepts of oil geology, utilizing, for this purpose, the material presented in the two earlier data-based volumes. To conform to the original standard set for it, this book has been kept relatively free from factual data and has been compiled rather as a summation, based upon the best available evidence, of present knowledge of the science. This volume does not include a discussion of the technique of field or laboratory geology, but does include papers divided into 7 parts: History; Origin and evolution of petroleum; Migration and accumulation of petroleum; Relations of petroleum accumulation to structure; Porosity, permeability, compaction; Oil-field waters; and Subsurface temperature gradients.