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Problems with CO2 Sequestration

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  • Tom Catino
    Potential Leakage and Toxicity Problems with CO2 Sequestration 31 July 2006 Cross-well seismic difference tomogram of the Frio Brine project shows the CO2
    Message 1 of 1 , Aug 1, 2006
      Potential Leakage and Toxicity Problems with CO2 Sequestration
      31 July 2006

      Cross-well seismic difference tomogram of the Frio Brine project
      shows the CO2 plume.
      Results from a field test on CO2 sequestration in an old brine-
      filled oil reservoir suggest that the mixture of CO2 and brine
      dissolves minerals in the rock walls, including carbonate, that
      could lead to pathways in the rock through which the gas could

      In a paper published in the July edition of Geology, the researchers
      in the Frio Brine Pilot also note the potential for the mobilization
      of toxic trace metals and toxic organic compounds.

      The Frio Brine Pilot was the first test of closely monitored CO2
      injection in a brine formation in the United States, and was funded
      by the Department of Energy (DOE) National Energy Technology
      Laboratory (NETL) under the leadership of the Bureau of Economic
      Geology (BEG) at the Jackson School of Geosciences, The University
      of Texas at Austin, with major collaboration from GEO-SEQ, a
      national lab consortium led by Lawrence Berkeley National Laboratory

      The researchers injected 1,600 metric tons of CO2 1,500 meters down
      into a sandstone site representative of a target for large-volume
      storage. The sandstones of the Oligocene Frio Formation are part of
      a thick, regionally extensive sandstone trend that underlies a
      concentration of industrial sources and power plants along the Gulf
      Coast of the United States.

      Monitoring strategy at Frio.
      The team then measured and monitored the CO2 plume using a diverse
      suite of technologies in three intervals: the injection zone, the
      area above the injection zone, and the shallow near-surface

      Each monitoring strategy used a preinjection and one or more
      postinjection measurements. Wireline logging, pressure and
      temperature measurement, and geochemical sampling were also
      conducted during injection, and at follow-up intervals subsequent to
      the injection.

      While the sequestration to-date has been successful—there have been
      no detected CO2 leakages—the researchers conclude in their latest
      published assessment of on-going findings and analysis that the
      chemistry of the process might prove problematic.

      Fluid samples obtained from the injection and observation wells
      before CO2 injection showed a Na-Ca-Cl–type brine with 93,000 mg/L
      total dissolved solids (TDS) at near saturation with CH4 at
      reservoir conditions.

      Following CO2 breakthrough, samples showed sharp drops in pH (6.5–
      5.7), pronounced increases in alkalinity (100–3,000 mg/L as HCO3)
      and Fe (30–1,100 mg/L), and significant shifts in the isotopic
      compositions of H2O, dissolved inorganic carbon (DIC), and CH4.

      Geochemical modeling indicates that brine pH would have dropped
      lower but for the buffering by dissolution of carbonate and iron

      This rapid dissolution of carbonate and other minerals could
      ultimately create pathways in the rock seals or well cements for CO2
      and brine leakage. Dissolution of minerals, especially iron
      oxyhydroxides, could mobilize toxic trace metals and, where residual
      oil or suitable organics are present, the injected CO2 could also
      mobilize toxic organic compounds.

      Environmental impacts could be major if large brine volumes with
      mobilized toxic metals and organics migrated into potable
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