In considering the accumulation of oil and gas in limestone reservoirs according to the theories involving capillarity, water circulation or gravitational adjustment, one is faced by many difficulties in explaining migration through impervious rocks surrounding the reservoir. It is therefore suggested that oil-forming organisms collected within the reservoir itself and the area immediately tributary thereto, and that there is consequently no true distinct source rock. Neither is there any necessity for accounting for any migration excepting within the porous limestone itself.
The accumulation of oil in limestone may be effected in various ways, depending on the nature of the openings in the limestones. These openings may be classified as: (1) fractures; (2) primary porosity; and (3) secondary porosity, (a) with partial later cementation, and (b) without later cementation.
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.