PNNL

Abstract

The Middle (?)-Upper Cambrian Mt. Simon Sandstone formation has long been recognized as a significant deep saline reservoir in the Midwest, USA and is now recognized as a major Geological Sequestration target. The Mt. Simon injection zone in Michigan consists primarily of sandy clastics, overlies a diverse Precambrian basement complex, and grades upwards to fine-grained, shaley clastics and interbedded carbonate strata of the Eau Claire Formation, a regional confining zone. The top Mt. Simon lies at depths ranging from about 3000ft (914m) to more than 15,000ft (4572m) in the central Michigan basin. Formation thickness ranges from a maximum in excess of 1,300ft (396m) to near zero adjacent to basement highs in the southeast. The Mt. Simon has variable reservoir quality characteristics dependant primary on facies variations and depth related, diagenesis. On the basis of well log-derived net porosity from wells in Michigan a conservative estimate of total geological sequestration capacity in the Mt. Simon was determined to be in excess of 29 Gmt. The majority of this geological sequestration capacity is identified in the southwestern part of the state. Numerical simulations of CO2 injection were conducted using the STOMP-CO2 simulator to assess the potential for geologic sequestration in the Mt. Simon Sandstone saline reservoir in Holland, Ottawa Co., Michigan. The simulation used a CO2 injection period of 20 years at a rate of 600,000 mt/year, followed by an equilibration period of 280 years, for a total of 300 years. After 20 years, the total amount of CO2 injected is 12 Mmt; after 300 years, 9.8 Mmt is free (non-entrapped) supercritical CO2, 0.7 Mmt as entrapped supercritical CO2 and 1.5 Mmt dissolved into the brine. The supercritical CO2 has spread to a radius of 5905 ft (1.8 km) after 20 years of injection, and to a radius of 12,467 ft (3.8 km) after 300 years. The low-permeability Eau Claire retards upward migration of CO2. Pressures during injection at the bottom of the caprock (1540.5 m; 5054 ft depth) are well below the fracture pressure limit of 4046.6 psi (27.9 MPa), assuming a fracture pressure gradient of 0.8 psi/ft (0.018 MPa/m) due to the high permeability of the Mt. Simon.