Silurian-Niagaran Reef Belt Around the Michigan Basin—A Synergistic Review

Abstract

ABSTRACT The Silurian-Niagaran pinnacle reefs occur on a belt which encircles the entire Michigan Basin including areas presently covered by the Great Lakes. The annual production from these reefs in Michigan has reached 30 million barrels of oil and 150 billion cubic feet of natural gas. Two different structural settings existed in the Michigan Basin during the Silurian Period, which resulted in formation of the pinnacle reefs with somewhat different characteristics in different parts of the basin. The pinnacles of the northern trend occur at depths of 4000-7000 feet, are up to 700 feet thick, and average about 100 acres in area. The southern pinnacles occur at depths of 2000–3000 f shorter, about 300 feet thick, and attain larger areas. The pinnacle reefs underwent several diagenetic changes, which resulted in concentration of the majority of the hydrocarbon reserves of the northern trend in pinnacles which occur on a band 3-4 miles wide inside the middle of the trend. There exists a regional partitioning of oil and gas in the northern pinnacle reefs, which can best be explained by Gussow Theory of migration and differential entrapment. Such a reserve concentration or hydrocarbon differentiation has not been observed in the southern trend. A probabilistic model for exploration in a play was found applicable in mature areas of the northern trend and the results were extended to other parts. The results suggest that the effectiveness of exploration, based on seismic surveys, is 8 to 10 times better than random drilling. The reserves of the reef belt are in excess of 7 billion barrels of oil and 15 trillion cubic feet of natural gas in place.