Quantitative Evaluation Model of Water Blocking Damage in Low Permeability Gas Reservoirs

In this study, the goal was to quantitatively evaluate the potential water locking damage in low permeability gas reservoirs. To do so, a quantitative evaluation model for water locking damage in low permeability gas reservoirs was established based on the relative permeability and starting pressure gradient models. In the doing so, we analyzed the influences of water locking damage depth, starting pressure gradient and stress sensitivity on the water blocking damage degree. The analysis results suggested that the predicted results are better matched with the data of water locking damage experiment in tight sandstone. The greater the depth of water locking damage, the more serious the potential water locking damage; the larger the fluid starting pressure gradient, the more difficult for the liquid phase to cleanup. Herethe fluid cleanup efficiency could be improved by adding surfactant. A cleanup differential pressure is beneficial to liquid phase cleanup, while stress sensitivity may exaggerate the water locking damage, especially when the starting pressure gradient is low. Studies showed that water locking damage is the synergistic effect of reduced gas phase relative permeability caused by water phase retention and reduced absolute permeability caused by stress sensitivity, and the reasonably determined cleanup differential pressure is conducive to alleviating the water locking damage in low permeability gas reservoirs.