致密砂岩储层压裂液损害机理探讨

Discussion on damage mechanism of fracturing fluid in tight sandstone reservoir

大牛地气田储层为典型的致密砂岩储层,自然产能低。在压裂过程中,压裂液不可避免地进入储层,造成储层损害从而影响压裂效果。文中针对工区低孔、低渗、低压、黏土矿物丰富、毛细管力高、局部存在超低含水饱和度等特征,开展了压裂液室内评价实验,深入分析了液相圈闭、固相侵入、黏土矿物运移、敏感性损害、压裂液与储层的配伍性等因素对储层损害的影响。实验表明:液相圈闭和固相损害是造成储层损害的主要原因;毛细管自吸、黏土矿物运移、碱敏和固相沉积等加剧了液相滞留和孔喉堵塞,减小了孔喉有效渗流,使得储层渗透率下降;储层物性越差,非均质性越强,液相滞留越严重,造成储层损害严重,返排效果越差。

Daniudi Gas Field is a typical tight sandstone reservoir. It has low nature production capacity without hydraulic fracturing. In the proeedure of hydraulic fracturing, fracturing fluid enters the reservoir inevitably, resulting in a series of reservoir damages and affecting the fracturing effect. According to the engineering geological characteristics of low porosity, low permeability and low pressure, rich in clay minerals, high capillary force anti local ultra-low water saturation in work area, and through a lot of lab experiments on fracturing fluid evaluation, this paper makes a deep analysis of the influences of liquid phase trapping, solid invasion, clay minerals migration, sensitivity damage, the fracturing fluid and reservoir eompatibility on reservoir damage. The resuhs show that liquid phase trapping and solid phase danmge are the main reasons of reservoir damage. Capillary imbihition, clay mineral migration, alkali sensitivity and solid phase deposition exacerbate liquid phase residenee and pore throat blocking, reducing the effective seepage of pore throat and decreasing the reservoir permeability. The poorer the reservoir physical property is, the stronger the heterogeneity is. The more serious the liquid phase residence aml the reservoir damage are, the worser the backflow effect of fracturing fluid is.