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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 66 (1982)

Issue: 10. (October)

First Page: 1686

Last Page: 1687

Title: Electro-Magnetic Oil Exploration Research Using Commensurate Frequency Previous HitPhaseNext Hit Difference Technology: ABSTRACT

Author(s): Donald B. Daniel

Article Type: Meeting abstract


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This paper defines and develops the characteristics of instrumentation that exploit the concepts of CFT (commensurate frequency technology), a modern application of frequency-domain electromagnetics. CFT instrumentation can operate in all modes (i.e., quasi-static, near field, or far field). In all modes, the Previous HitphaseNext Hit difference between commensurate frequencies is measured to produce a signature relating only to geologic variations. Unlike classical EM measurements, which are apt to be dominated by near-surface features, the CFT process minimizes the effects of near-surface features by common mode rejection (CMR). This characteristic is clearly substantiated by comparison of CFT data and classical EM data.

"Previous HitPhaseNext Hit" is an ambiguous subject that means different things to different people, and there are differences between Previous HitphaseNext Hit sensitive detectors and Previous HitphaseNext Hit meters. There are unique benefits and limitations to use of a Previous HitphaseNext Hit meter.

Pioneering work has been done using GeoDecca instrumentation and the resulting data show that there is a distinctive, frequency-domain signature associated with a significant number of oil and gas fields in southern California. Recent work using GeOmega instrumentation shows that measurements of commensurate frequency Previous HitphaseTop difference are insensitive to near-surface pipelines that produce significant distortion of classical EM data taken at the same time and same place. Field data also show the signature enhancement that results when radio signals from four different directions are stacked to produce a composite signature. This will not surprise those who understand that the apparent electrical characteristic of the earth depends on the direction of arrival of electromagnetic waves. T is complicates life and one might wish that it were not true, but field data clearly indicate the benefits of illuminating the earth with multiple frequencies from multiple directions.

The shallow skin depth of current GeoDecca (VLF) and GeOmega (LF) sensors is acknowledged. However, a question that cannot be answered at this time is "why the sensors produce a significant signature above a number of California oil fields where the oil and gas are commonly 10 or more skin depths in the earth."

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Copyright 1997 American Association of Petroleum Geologists