Predicting the flux of CO2 along a leaking wellbore requires a model of fluid properties and of transport along the leakage pathway. This model should accurately represent the geometry of any discrete leakage pathway, because this geometry strongly affects the coupling between geochemical reactions and geomechanical response. Validating a transport model in advance of large-scale sequestration is difficult because instances of CO2 plumes reaching abandoned wells are presently rare. However, natural gas leakage events along wellbores can provide insights into conductive pathways analogous to those anticipated for CO2 sequestration. We apply a simple transport model to field measurements of sustained casing pressure (SCP) vs. time. We treat as unknowns the effective permeability of the leakage path and the depth at which leakage into the wellbore is occurring. These parameters are useful for forecasting likely leakage rates in sequestration sites located near oil and gas fields and for choosing candidate sites based on past exploration history. For several cases of SCP, conductive pathways (e.g. open fracture, gas channel, micro annulus) must exist to explain the large inferred values of effective permeability. Applied to a large enough set of SCP wells, this approach can provide a probabilistic distribution of leakage rates given regional and well parameters. For CO2 sequestration purposes this provides a tool to assess the risk associated with carbon dioxide migration along leaky wells, which is necessary for site selection, permitting, and properly crediting sequestration operations.

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