酸预处理在水力压裂中降低伤害机理研究

A Study on Damage Reduction Mechanism of Acid Preflushing During Hydraulic Fracturing

低渗透储层进行常规加砂压裂常常由于压裂液破胶不彻底、残渣和滤液伤害等问题而影响压裂改造效果。压裂前的酸预处理技术可降低压裂过程中伤害,改善压裂效果。利用激光粒度仪对常规压裂液破胶与酸性环境下压裂液破胶过程中瓜胶分子尺寸进行定量观测,研究不同破胶环境下岩石基质伤害的主要因素;通过电镜扫描对注入破胶液与酸液后伤害的岩芯进行微观分析。研究表明,在酸液存在条件下压裂液破胶后瓜胶分子尺寸大幅度降低,瓜胶分子尺寸的降低比酸性环境对降低岩石渗透率伤害贡献更大,酸液能够很好地解除压裂液伤害,提高岩芯渗透率,同时由于酸溶蚀可形成较为明显的溶蚀孔道,进一步提高基质渗流能力。

Hydraulic fracturing is an effective way to develop low permeability reservoir.However,halfway gelout,fracturing fluid residue and filtrate damage often reduce stimulation effect.On-site application of acid pretreatment fracturing technology has been proved to be able to reduce damage during fracturing,but the damage reduction mechanism of acid pretreatment remains unclear.In this paper,molecular dimensions of guar gum under both conventional and acidic conditions are quantitatively observed by using laser particle analyzer（LPSA）.Principle factors affecting the damage of gelout fluid to matrix in acidic environment are also researched here.In addition,microanalysis of damaged core edge after injecting gelout fluid and acid fluid is conducted by means of scanning electron microscope（SEM）.We can draw conclusions from the results：molecular dimension of guar gum after gelout is significantly reduced under acidic condition,and the reduction of molecular dimension plays more important role than acidic environment in decreasing damage;acid fluid is able to effectively remove damage caused by fracturing fluid,increase core permeability,and form corrosion channels.