Geologic Occurrence of Oil and Gas in Montana
The Great Plains of Montana contain many structural features apparently favorable for oil and gas accumulation, but tests of most of them have disclosed only a small number of important fields. The region is characterized by several isolated mountainous groups of diversified origin, each being essentially a complete structural unit. Oil and gas are produced from formations ranging in age from early Mississippian to Upper Cretaceous. The producing structural features are various types of anticlines, noses, and terraces. The major tectonic movements responsible for the development of most of these structural features took place sometime in the Eocene subsequent to the deposition of the Fort Union formation. The major factors responsible for oil and gas accumulation are anticlines and domes, lenticular sandstones, porosity, faults and circulating ground water.
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.