OIL FIELDS AND AEROMAGNETIC ANOMALIES

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Abstract
Six examples of relationships between aeromagnetic anomalies and producing areas are presented by maps of subsurface structure, observed aeromagnetics, second vertical derivatives of the aeromagnetic fields, and maps of the magnetic basement computed from the aeromagnetic data whenever all these are available. In addition, a copy of an original aeromagnetic traverse is included. The examples embrace Puckett in the Delaware Basin of West Texas, Grieve in the Wind River Basin of Wyoming, Tioga and Onstad in the Williston Basin of North Dakota, Swanson River in the Cook Inlet Basin of Alaska, and Zelten in the Sirte Basin of Libya. These include both “before and after” examples with basement maps prepared in some cases before discoveries, and in other cases afterwards. The paper purports to demonstrate that correlative magnetic anomalies exist in either event. Moreover, these anomalies would be disclosed by any competent technique, so techniques of interpretation are not a part of the argument. It is well known that the larger observed aeromagnetic anomalies result from intrabasement contrasts of magnetization. Anomalies resulting from structure alone ordinarily are smaller by a factor of the magnitude of ten. Of the six cases, Puckett, Tioga, and Onstad represent structures with associated intrabasement effects, whereas anomalies at Grieve, Swanson River, and Zelten are considered to be purely structural effects. There are difficulties involved in using either type of anomaly quantitatively for determination of depth to basement and the relief of possible basement structure. But these examples are part of a much larger amount of evidence which seems to justify improving the definition of the observed aeromagnetic field so that the small residual structural effects can be better defined in order to find more of them and to interpret them more accurately. New instrumentation with higher sensitivities is now available for this second venture in aeromagnetic prospecting.

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