Interpreting Silurian Niagaran Reefs In The Michigan Basin

Productive Michigan Basin reefs were discovered in 1889 by random drilling. The pinnacle reef trend became active in southwestern Ontario in 1947, expanding to southeastern Michigan in 1952. The current exploration play began in northern Lower Michigan in 1969, and soon after in southern Michigan. Michigan reef log interpretation is highly dependent on empirically derived methods, as conventional charts do not adequately cover saturated sodium chloride salt muds and hypersaline formation waters. Hypersaline is defined as salinity much greater than 260,000 ppm total salt burden at 25ø C. The higher burdens in Michigan are a result of significant amounts of calcium chloride along with sodium chloride salts. As both the density and neutron logs are affected by hypersaline conditions, a FDC-CNL cross plot chart with a rh of of 1.20 gm/cc was constructed. The proper solution of Archie's water saturation equation requires an m value substantially greater than 2.0. Empirical studies lead to the Niagaran reef "variable m" exponent used in "Quick Sw" charts.