Synergistic Interpretation of Near-Surface Magnetic Anomalies and High-Frequency Seismic Data, Northeastern Montana

John A. Andrew, Robert J. Graf, Douglas P. O'Brien, Richard J. Wold

A low-altitude (300-ft), close-spaced (4 lines/mi) airborne magnetic gradiometer survey was flown in a 1,000-mi² area in northeastern Montana. The area contains 31 oil fields and a modern high-frequency, broad-bandwidth seismic data set. The aeromagnetic survey was designed specifically to study and analyze the short-wavelength, small-amplitude magnetic anomalies associated with near-surface magnetic sources. Some near-surface magnetic sources may be related to epigenetic changes associated with seeps from hydrocarbon reservoirs.

All 31 oil fields had a near-surface magnetic anomaly. Other near-surface magnetic anomalies had an obvious seismic anomaly visible on the high-frequency, broad-bandwidth seismic data available in the area. In addition, the zones offsetting the observed near-surface magnetic anomalies can be seen in the seismic data, suggesting a small, but deep-seated Quaternary or Holocene wrench-fault system. Many of the magnetic offset zones were also visible in available Landsat data. These offset zones may provide the vertical migration paths for reservoir seeps.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.