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Geophysical Monograph Series



  • Carbon sequestration
  • Carbon cycle (Biogeochemistry)

Index Terms

  • 1615 Global Change: Biogeochemical cycles, processes, and modeling
  • 1694 Global Change: Instruments and techniques
  • 1829 Hydrology: Groundwater hydrology
  • 1847 Hydrology: Modeling



Scoping calculations on leakage of CO2 in geologic storage: The impact of overburden permeability, phase trapping, and dissolution

C. Doughty and L. R. Myer

The purpose of this chapter is to examine fundamental aspects of potential leakage of CO2 from geological sequestration reservoirs. Numerical simulations of fluid and heat flow are conducted to evaluate the rate at which a plume of CO2 moves upward through the subsurface and the amounts of dissolution and phase trapping (called “residual gas trapping” in other chapters) that occur along the way. A quantity of CO2 is injected into a 1000-m deep, 100-m thick permeable formation saturated with saline water, where it forms an immiscible, supercritical fluid phase and partially dissolves in the aqueous phase. As the supercritical CO2 moves upward, it smoothly transitions into a gas. Between the injection interval and the ground surface, the overburden is assumed to be homogeneous. For overburden vertical permeabilities of 100 md (∼10−13 m2), 10 md (∼10−14 m2), and 1 md (∼10−15 m2), using a numerical simulator that incorporates hysteretic relative permeability and capillary pressure functions, 1000-year simulations are conducted. For each permeability, simulations are carried out for a range of maximum residual gas saturations (Sgrmax), which plays a key role in phase trapping and is poorly known for aqueous/CO2 systems. The time required for the CO2 plume to reach the surface increases with decreasing overburden permeability and increasing Sgrmax. Tradeoffs exist between three key mechanisms for CO2 trapping: stratigraphic trapping, phase trapping, and dissolution trapping. Low overburden permeability promotes stratigraphic trapping but hinders phase or residual gas trapping and dissolution trapping by keeping the CO2 plume compact. High overburden permeability enables the plume to move upward more readily, but any attendant spreading promotes phase and dissolution trapping. A large value of Sgrmax promotes phase trapping but hinders dissolution trapping by minimizing contact between brine and immiscible (free-phase) CO2. Additional simulations, including a high-permeability conduit in an otherwise low-permeability overburden, provide insights into the effects of geologic heterogeneity, which can greatly shorten the time required to reach the surface.

Citation: Doughty, C., and L. R. Myer (2009), Scoping calculations on leakage of CO2 in geologic storage: The impact of overburden permeability, phase trapping, and dissolution, in Carbon Sequestration and Its Role in the Global Carbon Cycle, Geophys. Monogr. Ser., vol. 183, edited by B. J. McPherson and E. T. Sundquist, pp. 217–237, AGU, Washington, D. C., doi:10.1029/2005GM000343.

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