低渗透气藏水锁损害定量评价模型

为了定量评价低渗透气藏潜在的水锁损害，基于相对渗透率和启动压力梯度模型，建立了低渗透气藏水锁损害定量评价模型，分析了水锁损害深度、启动压力梯度和应力敏感对水锁损害程度的影响。分析发现，该模型的预测结果与致密砂岩水锁损害实验结果吻合较好；水锁损害深度越大，潜在的水锁损害程度越严重；流体启动压力梯度越大，液相越难以返排，添加表面活性剂能够提高流体返排效率；高返排压差有利于液相返排，但应力敏感可能导致水锁损害程度增大，在启动压力梯度较低时影响尤其明显。研究结果表明，水锁损害是水相滞留引起的气相相对渗透率降低与应力敏感导致的绝对渗透率降低协同作用的结果，确定合理的返排压差能够减轻水锁对低渗透气藏的损害。 

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.