SORPTION BEHAVIOR OF INDIANA COALS AND THEIR CO2 SEQUESTRATION POTENTIAL

Sequestration of anthropogenic carbon dioxide into geological formations may represent a plausible solution for reducing the amounts of CO₂ currently emitted into the atmosphere. Abandoned oil and gas fields, deep saline aquifers, shale units, and unminable coal seams are the preferred candidates for geological sequestration.  Significant attention has been paid to the unminable coals as they appear to have a twofold beneficial effect. First, carbon dioxide appears to be tightly sorbed into the molecular structure of the coal. Second, as demonstrated both on a laboratory and field scale, the displacement of methane occurs when CO₂ is sorbed, thus creating an additional supply of natural gas.  Studies in high-rank coals have demonstrated a CO₂/CH₄ adsorption ratio of 2:1. Recent studies on lower-rank coals suggest much higher ratios and a possible dependency on maceral composition. These studies indicate that the influence of rank and maceral type on sorption needs further evaluation.

The sorptive and compositional characteristics of Indiana’s high-volatile bituminous C-rank coals are being investigated. Preliminary assessment of the Pennsylvanian Springfield (Petersburg Fm.) and the Seelyville (Linton Fm.) coal seams in Indiana suggest that they could sequester nearly 10.2 million metric tons of CO₂. These calculations are based on standard adsorption isotherm analyses performed on crushed coal samples. Currently, an investigation is being conducted on uncrushed core samples of coals at controlled reservoir temperature and pressure conditions in order to more closely approximate in-situ adsorbed CO₂ volumes.