TESTING CARBON STORAGE IN THE MISSISSIPPIAN/DEVONIAN BLACK SHALES OF THE APPALACHIAN, ILLINOIS, AND MICHIGAN BASINS

Black shales are continuous, low permeability units that are commonly considered to be regional seals in petroleum exploration. The Devonian Antrim (Michigan Basin), New Albany (Illinois Basin), and Ohio (Appalachian Basin) Shales are organic-rich gas shales that may provide CO₂ storage and enhanced natural gas recovery. In gas shales, significant amounts of natural gas are adsorbed onto dispersed organic matter. When injected into the shale, CO₂ is expected to displace that natural gas and trap the CO₂ analogous to the processes associated with enhanced coalbed methane recovery. These shales are being characterized and their CO₂ capacity assessments are being compiled for the U.S. Department of Energy-funded Regional Sequestration Partnerships. Shales in the study occur at a drilling depth of 1,000 feet or deeper and have a thickness of 100 feet or more. CO₂ and CH4 adsorption isotherms for the Ohio and New Albany shales are being acquired. Adsorption isotherm cumulative probability curves indicate that at a reservoir pressure of 400 psi, the CO₂ adsorption capacity for these shales is 21.98 standard cubic feet of CO₂ per U.S. ton of shale (scf/ton, 10^th percentile), 42.9 scf/ton (50^th percentile), and 83.6 scf/ton (90^th percentile). A GIS analysis of shale storage capacity has been completed using the 10^th percentile value to reflect uncertainty associated with the low injectivities of a reservoir with permeabilities in the micro- to nanodarcy range. As much as 247 gigatonnes (Gt, billion metric tonnes) of CO₂ might be sequestered in these shales: 21 Gt in the Antrim Shale of the Michigan Basin; 15 Gt in the New Albany Shale of the Illinois Basin; and 211 Gt in the Ohio Shale of the Appalachian Basin.

In an August, 2007, special session, the Kentucky Legislature passed House Bill 1, a coal to liquids and coal gasification incentive bill. The bill provides funding and mandates carbon storage research in several areas including a test of the CO₂ storage and enhanced natural gas recovery possibilities in the Devonian Shale. Within the Kentucky Consortium for Carbon Storage, an experimental protocol to test this concept is being designed and well selection criteria are being established.