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The Use of Microgravity Data to Increase the Success of Niagaran Reef Exploration in the Michigan Basin

A. W. Hinks and R. L. Schulz
Westshore Consulting, Muskegon, MI

Although the Michigan Basin is considered a mature hydrocarbon play, new Niagaran reef reservoirs are regularly discovered. A significant reason that a number of reefs remain undiscovered is because glacial drift and underlying scoured bedrock limit the signal-to-noise ratio of geophysical methods. Seismic methods are limited by energy attenuation in drift and scattering of energy at the scoured drift/ bedrock contact. Bouguer gravity data allows subsurface density variations to be identified, and has been used successfully to locate reefs, but is severely limited by scouring on the drift/bedrock contact.

Microgravity data is precise, densely sampled Bouguer gravity data that is being used to improve exploration success. The shallow density variations caused by drift-filled scours produce high frequency gravity anomalies, while deeper density variations cause lower frequency anomalies. Because microgravity data samples the high frequency content of gravity anomalies, gravity anomalies caused by scours can be identified by their frequency content.

Once scours are identified, that information can be used to highlight areas where seismic data should be questioned or receive additional processing and interpretation. Additionally, the identification and segregation of high frequency gravity anomalies often allows deeper-sourced broader gravity anomalies, like those caused by Niagaran reefs, to be reliably identified. Once the probable source of gravity anomalies is identified, the direct identification of Niagaran reefs from microgravity data can aid in the development of prospects in areas where seismic data is expensive and/or quality seismic data cannot be acquired.

AAPG Search and Discovery Article #90900©2001 AAPG Eastern Section Meeting, Kalamazoo, Michigan