Abstract

The reflection seismic method has proven to be an excellent technique for locating and mapping Silurian reef buildups in northern Michigan. Current industry estimates of total discovery volumes are 400 to 600 million barrels of oil and 3 to 5 trillion cu ft of gas. Production is from carbonate buildups (reef pinnacles) whose areal extents range from 40 to 600 acres at depths of 3000 to 7000 ft. Extending northeast-southwest across the northern part of Michigan, the reef trend is 10 to 20 miles wide. Reef heights increase basinward from the shelf margin, growing to a maximum of 600+ ft. Reef porosity throughout the trend is variable, ranging from 5 to 30 percent, depending upon a combination of diagenetic processes.Reefs grew on a ramp from the Niagaran shelf edge to a flat basinal plain. A series of salt and carbonate beds were deposited around and over these carbonate buildups. Anomalies are recognizable from seismic data because the inter-reef section produces a strong characteristic seismic event which becomes weak and disrupted in the presence of a buildup. The Niagaran shelf margin can be mapped because it produces a seismic response similar to that of a pinnacle reef.In some areas, seismic interpretation is difficult due to high noise levels and distortion of seismic data by the irregular distribution of Pleistocene glacial deposits. Data quality has been improved through a combination of field techniques, common-depth-point stacking, static correction refinement, and filtering.

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