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| Fig. 1: Michigan basin geology. [3] (Source: Wikimedia Commons) |
The Michigan Basin has been a focus for oil and gas production for decades. The oldest deposits of this region have Precambrian rock formations, whereas the youngest sediments are from the Late Jurassic geological period. Most of the produced and producing fields are carbonate rocks from the Middle Ordovician, Middle Devonian, and Middle Silurian ages. There are several oil fields which have been discovered, the first one being in 1886 although production did not actually start until 1926. During the following decades, production was focused on the Mississippian rocks, and in the 1950s, Devonian rocks were the major contributors to production. In the 1960s, oil and gas production was fixated in the Ordovician reservoirs, and during this decade, Niagaran Reefs were discovered in the southern region of Michigan. Since the 1970s, the Silurian has been the major producer in Michigan - it is the most prolific formation with good potential for future development. [1]
There are two main regions of focus for production in the Niagaran reefs: the Northern Fairway and the Southern Trend, as seen in Fig. 1. The Northern Fairway is at a more mature stage, with steady-to-decreasing drilling rate, whereas the Southern Trend has been explored less, making this a target for potential exploration in the future. The reef play alone has an Estimated Ultimate Recovery of 1 BBOE from over one thousand pinnacle reefs and undiscovered resources of 239 MMBO and 7,023 BCFG, making it the major target of exploration in Michigan. [2]
The Michigan Basin was formed primarily by three eustatic sea level fluctuations which occurred during the Niagaran (Wenlockian) and into the Ludlovian, approximately 420 mya. Reef evolution, such as continuous and episodic growth, and sea level variation are some controlling factors for the deposition and architecture of Silurian Pinnacle reefs. The reef fields are relatively small and recoverable reserves range from 0.03 to 0.12 MMBOE for oil and 0.5 to 4.5 BCFG for gas. [2]
The Niagaran reefs have a ninety-year history of exploration, first having been discovered in Ontario, Canada during the 1930s. It was not until three decades later that oil and gas were discovered in the United States Niagaran reefs. In the 1950s, exploration expanded to southeastern Michigan where many additional reefs were discovered. In the 1970s, increased development in seismic technology led to the discovery of the most successful prospects of the Southern Trend in Eaton and Ingham counties. Studies of the region showed that the boundaries of the Niagaran reef were farther than expected, extending beyond the shores of Lake Michigan and Lake Huron, covering most of the territory of the state of Michigan. The Niagaran reefs reservoir has good porosity and permeability in multiple facies but the heterogeneous nature of its geologic composition makes it a complex formation to exploit. Throughout the 1990s, most of the exploration in Michigan consisted of drilling and discovery wells in the Niagaran reefs. Originally, only two sections of the Niagaran reef were being explored, the Northern and Southern ends, but later discoveries in the western Michigan counties of Mason, Oceana and Muskegon confirmed the prediction of the reef extending to the east and under Lake Michigan. Development of this field has remained slow due to impediments such as lack of pipelines in the area and environmental issues. [1]
© Fatimah AlNasser. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] K. Aminian, L. Ameri, and R. Bomar, "Evaluation of Silurian-Niagaran Reef Belt in Northeastern Michigan," SPE Form. Eval. 2, 428 (1987).
[2] C. J. Schenk et al., "Assessment of Continuous Oil and Gas Resources in the Ordovician Collingwood Formation and Utica Shale of the Michigan Basin Province, 2019," U.S. Geological Survey, Fact Sheet 2020-3027, June 2020.
[3] C. M. Davis, Readings in the Geography of Michigan (Ann Arbor Publishers, 1964).
