State of Michigan Department of Conservation Gerald E. Eddy, Director Geological Survey Division William L. Daoust, State Geologist Information on Michigan Silurian Oil and Gas Pools

Michigan's first commercial oil field was discovered at Port Huron, St. Clair County, in 1886. By 1910, 21 shallow wells had been completed in the Dundee formation at depths of about 500 to 650 feet. In 1910 the daily production from this field amounted to about 10 barrels of oil per day, all of which was used locally in the manufacture of lubricants. However, it was not until 1925 when the Saginaw field was discovered that Michigan began to produce significant quantities of petroleum. The wells in the Saginaw field produced oil from the Berea sandstone, a Mississippian formation lying at a depth of about 1825 feet in the city of Saginaw. In 1927 on the western side of the state at Muskegon, oil and gas were found in the Dundee formation. By 1928 a Dundee oil field had been established near Mt. Pleasant in Isabella County. Since then more than 400 oil and gas accumulations have, been found in Mississippian, Devonian, Silurian, and Ordovician formations. In drilling to Devonian reservoir rocks, formations of Pennsylvanian and Mississippian age are penetrated. In the course of exploration, Mississippian and Devonian formations have received the most attention and are thus credited with a greater number of oil and gas pools. To date the Devonian formations have produced most of Michigan's petroleum and Mississippian formations have produced most of the gas. But, since 1942, Mississippian and Devonian oil production has steadily decreased, and Mississippian gas production has shown an annual decline which began about 1947, the peak year. In contrast, oil and gas production from Silurian and Ordovician rocks has increased in recent years. Exploitation of these rocks is not entirely new to Michigan since gas was produced from Silurian formations in St. Clair County as early as 1927, and some Ordovician oil was produced from wells in Monroe County as early as 1920. However, the productive history for these older formations essentially begins in 1938 for the Silurian, and in 1935 for the Ordovician, Silurian and Ordovician formations have been increasingly popular drilling objectives in recent years, especially in the shallower parts of the basin. Accordingly, as more exploration of these older formations has been done, more new pools have been found, and substantial gains have been made annually in the amount of oil and gas produced from them. Since i960 more than half of Michigan's annual oil production and nearly one-third of the annual gas production has come from Ordovician rocks. The large increase from Ordovician reservoirs is mainly due to the discovery and