Oil and gas reservoirs may be divided into two great groups, (i) those caused by local deformation with or without rupture of strata; and (2) those due to the varying porosity of rock. In the first group the container rock is uniform in lithology and continuous over wide areas. In the second group the container rock is characterized by variable lithology and by discontinuity.
All oil and gas reservoirs are closed. The open or terrace type of structure nowhere constitutes an oil trap, nor does it cause accumulation of oil in commercial quantities. It is not uncommon for more than one type of reservoir to be present in a single field, but this fact can be recognized only by detailed knowledge of subsurface conditions.
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.