CO₂ Injection and Reservoir Characterization: An Integrated Petrographic and Geochemical Study of the Frio Formation, Texas

K. A. McGuire and J. D. Grigsby
Ball State University, Department of Geological Sciences

The Gulf Coast Carbon Center (GCCC), a branch of the Bureau of Economic Geology of the University of Texas at Austin, has conducted CO₂ sequestration experiments in the Oligocene, Frio Formation at the South Liberty Oil Field, Dayton, Texas. Petrological examination of core samples from the Frio “C” and “B” sandstones, ranging in depth from 1500m-1657m classifies the sandstones as poorly cemented, subangular to subrounded, subarkoses with mean composition of Q₇₄F₁₈L₆. XRD analyses identify Illite/Smectite as the dominant clay with lesser amounts of Kaolinite. Measured core plug mean porosity is 32% (±3) and mean permeability is 1513mD (±872). Point count porosity, dominated by primary intergranular porosity, is 22% (±10). Formation waters, sampled during the sequestration experiment, exhibited a rapid decrease in pH and increases in alkalinity and dissolved metals. Additional XRD and SEM analyses will be used in an effort to identify the source of ions in solution (as a result of increased CO₂ concentrations). Rock-water interaction experiments will also be conducted. These data are essential in understanding the chemical changes occurring in the formation and assisting in a model simulation of the Frio’s chemical reactive properties, all in response to increased CO₂ concentrations. This research supports the GCCC’s CO₂ sequestration efforts, assessing the Frio Formation as a repository for anthropogenic CO₂, and ultimately, atmospheric CO₂ reduction.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas