Evaporative Clean-Up of Water-Blocks in Gas Wells

The flow of a gas in to a wellbore in a production well can result in the evaporative cleanup of water blocks. This occurs primarily due to the expansion of gas resulting in additional water being evaporated in the near wellbore region. This study presents for the first time, equations and a model to calculate the rate at which the water block is removed in both fractured and unfractured gas wells.It is shown that the removal of water by the expanding gas leaves behind a saturation profile that is qualitatively different for low and high permeability rocks. As a consequence the increase in gas relative permeability or the well productivity with time can vary substantially depending on the rock permeability and the well drawdown. The model allows us to compute the impact of evaporative cleaning on well productivity.It is seen that high permeability rocks clean up significantly faster. It is also observed that unfractured wells may require a very long time to cleanup. Large pressure drawdowns as well as the use of more volatile fluids such as alcohols result in significantly faster cleanup. A distinctive feature of the study is that the model equations are formulated and solved completely without the assumption of skin factors for the damage zone. Thus the prediction of cleanup rates can be made more accurately.