致密气藏中防水锁剂的筛选方法及其微观机理

致密气藏物性差，只有通过水力压裂才能获得工业产能。在压裂过程中，水相压裂液侵入储层后会产生水锁现象，对储层造成伤害，严重影响致密气藏的产量。在压裂液中添加防水锁剂可以有效降低水锁带来的伤害。为了揭示防水锁剂降低水锁提高产量的机理,本文以DME稀释微乳液为例，首先通过表面张力实验，测试了DME稀释微乳液的表面张力随浓度的变化关系，并得到最佳的添加浓度；然后通过接触角实验评价了DME稀释微乳液的改变润湿性作用；之后结合自发渗吸和渗透率恢复率实验证明了DME稀释微乳液的降水锁功能；同时借助核磁共振研究了渗吸过程中水相进入不同大小孔喉的顺序以及渗吸采收率。本文还建立了一种有效评价防水锁剂的方法，为现场施工筛选此类添加剂提供了指导。

Experimental on Mechanism of Reducing Water Blockage in Tight Gas Reservoirs

Due to the low permeability and porosity, effective development of tight gas reservoirs relies on hydraulic fracturing. During fracturing, the fracturing fluid enters into pore and pore throat, which can create water blockage therein and decrease the well productivity. Adding additive in the fracturing fluid is an effective method to reduce the water blockage. In order to find out the mechanism behind this method, several experiments were conducted; the DME micro-emulsion was taken as the additive. Firstly, surface tension test was conducted to acquire the relationship between the concentration of additive and surface tension, thus to obtain the optimal usage of additive. Secondly, the contact angle test was conducted to test the wettability alteration by the DME micro-emulsion. Thirdly, imbibition and permeability recovery tests were conducted to test if the DME could reduce the water blockage. Moreover, the distribution of water in large and small pores were obtained through the nuclear magnetic resonance (NMR). In this paper, a systematic method was established to screen the additive for reducing the water blockage during hydraulic fracturing. Meanwhile, the key properties of such type of additive was revealed.