Kalkaska

The Kalkaska Field CO₂-EOR project is located in Kalkaska County, Michigan, within the Michigan Basin, and represents one of the primary examples of CO₂ flooding in Midwestern carbonate reservoirs. Production targets Niagaran (Silurian) pinnacle reef carbonates, which consist of isolated reef buildups characterized by high porosity zones surrounded by tight evaporitic and carbonate sealing formations. These reefs form stratigraphic traps with strong structural confinement, making them suitable for miscible CO₂ injection and long-term containment. Discovered in the late twentieth century during development of Michigan Basin reef trends, the field followed the typical progression of primary production → waterflooding → tertiary CO₂ flooding to increase recovery from mature reservoirs. CO₂ injection improves oil recovery through miscible displacement mechanisms including oil swelling and viscosity reduction, while water-alternating-gas (WAG) cycles are commonly used to improve conformance within the vertically heterogeneous reef systems. CO₂ is injected through Class II wells and partially recycled through surface processing facilities, with retained volumes contributing to geologic storage through structural trapping, residual trapping, and dissolution within reservoir fluids. Niagaran reef reservoirs in the Michigan Basin are relatively deep and pressure-contained, with thick evaporite and shale sequences providing effective vertical seals. The isolated nature of reef buildups allows well-defined plume migration and containment, making Kalkaska and similar reef projects important analogs for CO₂ storage in confined carbonate systems.