Abstract

The Mount Simon Sandstone (Cambrian) is recognized as an important deep saline reservoir with potential to serve as a target for geological sequestration in the Midwest, United States. The Mount Simon Sandstone in Michigan consists primarily of sandy clastics and grades upward into the more argillaceous Eau Claire Formation, which serves as a regional confining zone. The Mount Simon Sandstone lies at depths from about 914 m (3000 ft) to more than 4572 m (15,000 ft) in the Michigan Basin and ranges in thickness from more than 396 m (1300 ft) to near zero adjacent to basement highs. The Mount Simon Sandstone has variable reservoir quality characteristics dependent on sedimentary facies variations and depth-related diagenesis. On the basis of well-log-derived net porosity from wells in the Michigan Basin, estimates of total geological sequestration capacity were determined to be in excess of 29 billion metric tons (Gt). Most of this capacity is located in the southwestern part of the state.

Numerical simulations of carbon dioxide (CO2) injection were conducted using the subsurface transport over multiple phases-water-CO2-salt (STOMP-WCS) simulator code to assess the potential for geologic sequestration into the Mount Simon saline reservoir in the area of Holland, Ottawa County, Michigan. At this locality, the reservoir is more than 260 m (850 ft) thick and has a minimum of 30 m (100 ft) of net porosity. The simulation used a CO2 injection period of 20 yr at a rate of 600,000 metric tons (t)/yr, followed by an equilibration period of 280 yr, for a total of 300 yr. After 20 yr, the total amount of CO2 injected is 12 million metric tons (Mt); after 300 yr, 9.8 Mt is modeled to remain as a free-phase (nonentrapped) supercritical CO2, 0.7 Mt is capillary-entrapped (residual) supercritical CO2, and 1.5 Mt dissolved into the brine. The injected CO2 spread to an area with a radius of 1.8 km (1.12 mi) after 20 yr of injection at a single well and to an area with a radius of 3.8 km (2.36 mi) after 300 yr. The low-permeability Eau Claire retards the upward migration of CO2. Pressures during injection at the bottom of the cap rock (1540.5-m [5054-ft] depth) are well below the fracture pressure limit of 27.9 MPa (4046.6 psi), assuming a fracture pressure gradient of 0.018 MPa/m (0.8 psi/ft) caused by the high permeability of the Mount Simon Sandstone.

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