MODELING EARLY-TIME GAS MIGRATION THROUGH CEMENT SLURRIES

This work identifies a mechanism that could be responsible for substantial gas invasion into a cemented column after placement. A model is developed to predict the risk for gas invasion and to aid in the design of a cement job suggesting a ''tail'' and a delayed ''lead'' slurry. The model provides the absolute theoretical migration height when cement properties and formation parameters are known. The work accounts for the calculation of the hydrostatic pressure drop, for the estimation of the inflow rates resulting from shrinkage and filtration, and for the description of the bubble-rise process. A sensitivity study on important design and well parameters is included.