低渗透储层水锁伤害及解除机理核磁共振实验研究

Experimental study on water-blocking damage mechanism and its solution mechanism in low permeability reservoirs by nuclear magnetic resonance

低渗储层由于孔喉细小,开发过程中入井液进入储层后容易造成严重的水锁伤害。在分析水锁原因的基础上,开展了水锁伤害评价实验,研究了水锁伤害变化规律,并首次应用核磁共振技术研究了表面活性剂解除水锁伤害的机理。实验结果表明:外来液侵入岩心后初期水锁伤害率高达85%以上,经返排后水锁伤害有较大幅度降低,水锁伤害程度与小孔隙中外来液的滞留量有较好的正相关关系;通过降低表面张力可以大幅度降低岩心水锁伤害率。通过实验认为可以通过核磁共振技术测得小孔隙中外来液的滞留量计算水锁伤害程度;提高返排量和降低入井流体的表面张力可以降低储层的水锁伤害。

The water-blocking will bring harm to low permeable reservoirs due to small pore and throat. Based on the water-blocking define and the reasons,the experiments to evaluate water-blocking damage were carried out.The surfactant was applied to reduce the damage of water-blocking, and the mechanism has been studied for the first time using nuclear magnetic resonance technology.The results show that the water-blocking damage of the core is over85 % at the early stage, and the damage is significantly reduced after driving by gas,and there is obvious positive correlation between water blocking damage and the quantity of injected fluid in small pores.The surfactant can lower the surface tension and completely eliminate the water-blocking damage.The experiment results demonstrate that the level of the water-blocking damage can be counted by quantity of injected fluid in small pores,and improving the flowing back rate and reducing the surface tension of the invasion fluid will significantly reduce the damage of water-blocking.