Until the past five years, little attention was given to the effect of the physical properties of rocks on accumulation and discharge of oil and gas. Consequently, although the importance of the physical properties of a reservoir rock, such as permeability, compaction, cementation, and adsorption, are now clearly recognized, their measurement and interpretation, especially as applied at depths of several thousands of feet, are far from satisfactory. It is the purpose of this introduction to review briefly the two papers presented in this group, and to point out the value to the oil industry of continued research on the physical properties of the reservoir and associated rocks.
In “The Importance of Compaction and Its Effect on Local Structure,” L. F. Athy summarizes the data on the compaction of muds and shales caused by various thicknesses of overlying sediments. A discussion is then given of the characteristics of local structures that may result from differential compaction over buried hills and huge sand lenses. It is also pointed out that any relatively competent bed, in a rising fold, will differentially compact overlying incompetent beds, such as shales. It naturally follows, wherever differential compaction has been of importance, that there should be a thinning of the sedimentary section above the axis of the local structure.
Whatever one’s reaction to the significance of differential compaction, conditions favorable for its operation are very common and should be considered by anyone studying the genesis and characteristics of folds.
It seems that, although differential compaction unaided by
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.