Richard I. Gibson, 1998. "Gravity and Magnetics in Oil Exploration: A Historical Perspective", Geologic Applications of Gravity and Magnetics: Case Histories, Richard I. Gibson, Patrick S. Millegan
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The first U.S. oil discovery using any geophysical method came in 1924 at Nash Dome, Texas, as a result of a survey with the Eötvös torsion balance. This gravity-measuring device was invented in 1888, and first was used for hydrocarbon exploration in Czechoslovakia in 1915 16. It was very slow to operate and was sensitive to near-surface irregularities, and these problems provided the impetus for developing a sensitive pendulum apparatus.
Wyckoff and Eckhardt tested a practical pendulum instrument in Kansas and Oklahoma in 1925 26. After joining Gulf in 1928, they refined and developed the tool and it was field-tested in Michigan in April 1930. Gulf and other companies tried other pendulum methods, but by July 1932 the Gulf (Wyckoff) pendulum was in regular operation. Cleveland Oil Field (Texas) was found by Gulf with this pendulum; Conroe Dome, which was invisible in torsion-balance data, also was defined. The pendulum was a great improvement, but still did not have the sensitivity and speed of operation required for efficient exploration. At their peak, pendulum crews could observe a maximum of about 250 stations per month. The next step was the gravimeter.
Apparently, Humble Oil tested the first gravity meter in the United States, in 1930, but never placed it in regular use. Gulf developed a gravimeter in 1932 35 which began routine operation in May 1935. This instrument was the first practical field gravimeter, with an accuracy of better than 0.1 milligal, and it was very fast to operate. The Gulf (Hoyt) gravimeter received general
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The idea for this book came from a perceived lack of recent, instructive examples of exploration-oriented interpretations of gravity and magnetic data. The Society of Exploration Geophysicists two volumes, Geophysical Case Histories, are probably closest in philosophy to this book. Published in 1948 and 1956, many of the examples in the Case Histories are relatively dated and specific to particular areas. We hope this new book provides an update that includes lessons about gravity and magnetic exploration that can be applied to many parts of the world. The Utility of Regional Gravity and Magnetic Anomaly Maps (SEG, 1985, W.J. Hinze, editor) contains some excellent papers dealing with tectonics that have clear bearing on hydrocarbon exploration, but no paper shows the relationships among hydrocarbon accumulations, exploration, gravity, and magnetics. Geophysical texts focusing on gravity and magnetics, including L.L. Nettleton's classics, include only a few (albeit often excellent) case histories, and many are dated.
Thus, this book's target audience is geologists and geophysicists in operations offices, actively involved in exploration at any level from basin analysis to prospect generation. Although most of the papers deal with hydrocarbon exploration, several papers relate to gravity and magnetic data in mining and environmental applications. A final section is included on new developments, the state of the art.
The book is not intended for gravity and magnetics specialists (although we hope they will find it interesting), or for geophysicists interested in theory, acquisition, and processing, unless those aspects are important to the geologic exploration problem and to the decisionmaking process.
We believe that the philosophical approach to interpretation is almost as important as some aspects of a technical interpretation itself. This book reveals the diversity of philosophies that gravity and magnetic interpreters embrace, as well as the common threads to which all interpreters aspire.
This book is not a textbook, although we have tried hard to highlight the exploration lessons inherent in each technical paper. Additional instructional aspects of the book are the glossary of gravity and magnetic terms, provided by Integrated Geophysics Corporation (with assistance from Richard Hansen of Pearson, DeRidder & Johnson) and an annotated bibliography, which has pointers to the rich literature of gravity and magnetics. Other short "lessons" can be found in stand-alone illustrations or short features throughout the book.
We thank Ray Thomasson for continual encouragement, suggestions, and prodding. Reviewers, whose efforts are appreciated greatly, include Dale Bird, Bill Pearson, Mark Odegard, and several anonymous reviewers. We appreciate the help of the AAPG, especially Ken Wolgemuth, in this, the first effort at serious book publication by the coeditors.