Earth Sciences Division Berkeley Lab
Fundamental and Exploratory Research Program
Annual Report 2000–2001
NUMERICAL SIMULATION TO STUDY MINERAL TRAPPING FOR CO2 DISPOSAL IN DEEP AQUIFERS Tianfu Xu, John A. Apps, and Karsten Pruess Contact: Tianfu Xu, 510/486-7057, tianfu_xu@lbl.gov
RESEARCH OBJECTIVES
Carbon dioxide (CO2) disposal into deep aquifers has been suggested as a potential means whereby atmospheric emissions of greenhouse gases may be reduced. As a prelude to a fully coupled treatment of physical and chemical effects of CO2 injection, we sought to analyze the impact of CO2 immobilization through carbonate precipitation.
which in turn is dependent on the reactivity of associated organic material. The accumulation of carbonates in the rock matrix and induced rock mineral alteration caused by the presence of dissolved CO2 lead to a considerable decrease in porosity. Figure 1 shows simulated mineral abundances and CO2 sequestration for Gulf Coast sediments.
APPROACHES
SIGNIFICANCE OF FINDINGS
We performed batch reaction modeling to simulate the geochemical evolution of three different aquifer mineralogies in the presence of CO2 at high pressure. Our modeling considered (1) redox processes that could be important in deep-subsurface environments, (2) the presence of organic matter, (3) the kinetics of chemical interactions between the host rock minerals and the aqueous phase, and (4) CO2 solubility dependence on pressure, temperature, and salinity of the system. The geochemical evolution under both natural background and CO2 injection conditions was evaluated. Changes in porosity were monitored during the simulations.
ACCOMPLISHMENTS
Modeling results indicate that CO2 sequestration by matrix minerals varies considerably with rock type. Under favorable conditions, the amount of CO2 that may be sequestered by precipitation of secondary carbonates is comparable with (and can be larger than) the effect of CO2 dissolution in pore waters. The precipitation of ankerite and siderite is sensitive to the rate of reduction of ferric mineral precursors such as glauconite,
These numerical models provide a detailed understanding of a particular geochemical system’s dynamic evolution. A critical evaluation of these modeling results can provide useful insight into sequestration mechanisms and control of geochemical conditions and parameters.
RELATED PUBLICATIONS
Xu, T., J. Apps, and K. Pruess, Analysis of mineral trapping for CO2 disposal in deep aquifers, Berkeley Lab Report LBNL46992, 2000. Pruess, K., T. Xu, J. Apps, and J. García, Numerical modeling of aquifer disposal of CO2, Paper SPE-66537, presented at SPE/EPA/DOE Exploration and Production Environmental Conference, San Antonio, Texas, February 2001.
ACKNOWLEDGMENTS
This work was supported by the Office of Sciences, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, of the U.S. Department of Energy, under Contract No. DE-AC03-76SF00098.
Figure 1. Mineral abundances and CO2 sequestration obtained with CO2 injected at 260 bar for Gulf Coast sediments
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