ANALYSIS OF DEVONIAN BLACK SHALES IN KENTUCKY FOR POTENTIAL CARBON DIOXIDE SEQUESTRATION AND ENHANCED NATURAL GAS PRODUCTION

摘要

Devonian gas shales underlie approximately two-thirds of Kentucky. In the shale, natural gas is adsorbed on clay and kerogen surfaces. This is analogous to methane storage in coal beds, where CO_2 is preferentially adsorbed, displacing methane. Black shales may similarly desorb methane in the presence of CO_2. Drill cuttings from the Kentucky Geological Survey Well Sample and Core Library are being sampled to collect CO_2 adsorption isotherms. Sidewall core samples have been acquired to investigate CO_2 displacement of methane. An electron capture spectroscopy log has been acquired to investigate possible correlations between adsorption capacity and mineralogy. Average random vitrinite reflectance (R_(0random)) data range from 0.78 to 1.59 (upper oil to wet gas and condensate hydrocarbon maturity range). Total organic content determined from acid-washed samples ranges from 0.69 to 4.62 percent. CO_2 adsorption capacities at 400 psi range from a low of 19 scf/ton in less organic-rich zones to more than 86 scf/ton in the Lower Huron Member of the shale. Initial estimates based on these data indicate a sequestration capacity of 5.3 billion tons of CO_2 in the Lower Huron Member of the Ohio Shale of eastern Kentucky and as much as 28 billion tons total in the deeper and thicker parts of the Devonian shales in Kentucky. Should the black shales of Kentucky prove to be a viable geologic sink for CO_2, the extensive occurrence of shales in Paleozoic basins across North America would make them an attractive regional target for economic CO_2 storage and enhanced natural gas production.