GEOLOGICAL CONTROLS ON RESERVOIR PROPERTIES AND CO2 SEQUESTRATION POTENTIAL IN THE LOWER-MIDDLE DEVONIAN SYLVANIA-BOIS BLANC INTERVAL, MICHIGAN BASIN, USA

The main objective of this study is a sedimentary and stratigraphic investigation of the lower-Middle Devonian Sylvania-Bois Blanc interval in the Michigan Basin for large scale, safe geological carbon sequestration. The “Sylvania Sandstone” is a proven brine aquifer as a result of decades of commercial brine extraction and spent brine re-injection in central Lower Michigan. Though substantial brine is produced from the “Sylvania Sandstone”, recent studies from 355 modern wire-line log suites and conventional core analysis data from 53 wells suggest that much of the production is from non-sandstone lithology (Rock, 2011).

The Sylvania-Bois Blanc interval is a lithologically complex mixed carbonate-siliciclastic system that contains a diverse range of lithofacies, including limestone, dolomite, cherty carbonate and sandstone, most of which have been subject to fabric-altering diagenesis. Core derived porosity and permeability data suggest that diagenesis has improved reservoir quality in the dolomitized and cherty intervals. Each of these lithologies contains variable reservoir properties and may all act as significant reservoirs.

Core observations, petrographic thin-sections, and chemical staining analysis suggest this interval was deposited in peritidal to shallow subtidal environments with normal marine salinity. Correlation of geophysical wire-line log response to core derived facies allows for the regional mapping of facies in the subsurface. Wire-line log analysis suggests that the Sylvania-Bois Blanc interval contains shoaling upward packages that are effectively compartmentalized both laterally (along depositional dip) and vertically due to facies changes seen in cross-section. This compartmentalization may be due to the carbonate depositional systems response to relative sea-level change.

Mercury-injection capillary-entry pressure analysis will help in the evaluation of reservoir lithofacies versus non-reservoir lithofacies along with assessing the migration and entrapment potential of injected CO₂ within the Sylvania-Bois Blanc interval. A pay-zone analysis using core-calibrated wire-line logs and reservoir facies characterization data will allow for more accurate CO₂ storage capacity estimates for the Sylvania-Bois Blanc interval.