The value of geothermal data as an aid to the oil geologist remains to be demonstrated, at least insofar as the direct discovery of individual oil pools is concerned. While Van Orstrand demonstrated years ago, in his work on the Salt Creek field of Wyoming, that in some instances isothermal contours below the surface of the earth quite faithfully reflect the structural conditions and, more recently, observations on salt domes in Texas have demonstrated temperature conditions that would be recognized as anomalous by any geologist familiar with the area, the facts that no data are available in advance of drilling, that even after wells are drilled significant measurements can be secured only occasionally, and that in spite of the years of work that have been devoted to the study of earth temperatures we are still far from a complete understanding of their significance, have combined to dull the interest of those who must measure their effectiveness in terms of new oil-field discoveries and who have, therefore, concentrated their attention on methods that are more speedy, more definite and less dependent on a multitude of circumstances than is the measurement of the geothermal gradient.
On the other hand, the science of petroleum geology, during the past few years, has left the narrow lane which led only to the discovery of obvious anticlinal structures, along which it traveled for decades after the anticlinal theory was first announced, and to-day geologists recognize that all facts which may throw additional light upon either the
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.