Juske Horita¹, James G Blencoe², David R Cole²

(1) Oak Ridge National Laboratory, Oak Ridge, TN
(2) Oak Ridge National Laboratory

ABSTRACT: Fundamental Geochemical Research on Long-Term Carbon Sequestration in Subsurface Environments

To properly assess the viability of long-term CO2 sequestration, accurate information is needed on the thermophysical properties, phase relations, stable-isotope systematics, and reaction kinetics of C-bearing fluids and minerals under subsurface conditions. Accordingly, we are performing various laboratory experiments to investigate: (i) the thermophysical properties and phase relations of CO2-CH4-H2O fluids; (ii) carbon and oxygen isotope partitioning during carbonate precipitation; and (iii) the utility of natural isotopic tracers in quantifying CO2 residence times, storage capacity and reaction mechanisms in the subsurface.

The ultimate aim of the research on CO2-CH4-H2O fluids is to develop a comprehensive equation of state for binary and ternary mixtures of CO2, CH4 and H2O at pressure-temperature conditions representative of those in deep gas fields and saline aquifers. To acquire the data needed to create the model, two unique, custom-designed devices at Oak Ridge National Laboratory (a high pressure vibrating-tube densimeter, and a hydrogen-service internally heated pressure vessel) are being used to measure the densities, excess molar volumes, miscibility limits and activity-composition relations of CO2-H2O, CH4-H2O and ternary CO2-CH4-H2O mixtures at P-T conditions near the vapor-saturation phase boundary in the H2O system.

To accurately determine the kinetics of carbonate precipitation from CO2-rich saline waters, and associated isotope partitioning, both inorganic and microbially mediated processes are being studied under environmental conditions encountered during CO2 injection into the subsurface. Our results indicate that the behavior of isotopes is affected by the composition of water and the precipitation rate of carbonate minerals. Preliminary results on carbon isotope partitioning between CO2 and hydrocarbon-saturated rock reacted statically at 25oC (an EOR injection scenario) suggest that a light isotopic component of CO2 may be retained in the reservoir, leading to isotopically heavier CO2 further down the flow path.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado