The Influence of CO₂ on New Albany Shale Pore Structure and Composition

Richard Lahann, Maria Mastalerz, and John A. Rupp
Indiana Geological Survey, Indiana University, Bloomington, IN 47405, [email protected]

To determine the possible influence of CO₂ on the pore structure and mineralogy of the New Albany Shale (Devonian-Mississippian), a series of experiments were conducted utilizing Indiana shale samples of varying TOC content at various conditions. After the shale samples were heated as high as 150^oC in Teflon-lined high-pressure reaction cells containing either distilled water or NaCl brine and CO₂, the reaction products were characterized by mesopore and micropore analysis, X-ray diffraction and SEM analysis of the shale residue, and fluid chemistry analysis of the reactant brine. Results from CO₂-saturated shale and distilled water showed no changes in shale pore structure relative to shale samples without CO₂ surface saturation.

A second series of experiments was run at 80^oC, using 50,000 ppm NaCl brine, 60-mesh ground shale (2:1 by mass), and varying amounts of solid CO₂ (dry ice). The pressure in the reaction cells was controlled by the partial pressure of CO₂ and ranged from 100 to 3500 psi. Postreaction brine samples showed up to thousands of ppm of K, Mg, and Ca in solution. The concentration of Ca and Mg in the brine tended to increase in proportion to the increasing partial pressure of CO₂. The same experiments using chips of shale from the New Albany showed lower concentrations of the cations in solution, but displayed a similar pattern of elevated increasing Ca and Mg with increasing CO₂ pressure. SEM examination of the shale chips confirmed the dissolution of carbonate-mineralized biogenic structures in the shale.

AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009