基于双尺度等效渗流模型的复杂碳酸盐岩蚓孔扩展形态研究

Wormhole dissolution pattern study in complicated carbonate rock based on two-scale continuum model and equivalent seepage theory

碳酸盐岩储层非均质性强,具有天然裂缝发育与孔渗分布复杂的特点,常采用酸化措施进行处理,在其间形成的酸蚀蚓孔形态必然受到储层复杂孔渗分布模式和天然裂缝的影响。因此,在双尺度连续模型的基础上结合等效渗流理论,分析了层内非均质性、层间非均质性与天然裂缝对蚓孔形态特征与注酸量的影响。结果表明:在不同的非均质程度情况下,均存在几乎相同的注酸速度可使蚓孔突破时的注酸量最小,且最小注酸量随非均质程度增加先减小后增加;高渗带的存在能显著减少蚓孔突破时的注酸量,但渗透率增高到一定程度后对注酸量减少的影响减弱;酸液流入天然裂缝后,蚓孔延伸方向由天然裂缝决定,平行于酸液流动方向的天然裂缝能够大幅度地降低酸液注入量,随着天然裂缝长度增加,注酸量呈现线性下降的趋势。该研究对碳酸盐岩储层基质酸化研究具有一定的指导意义。

Carbonate rock has great heterogeneity,and possesses the characteristics of complex physical property and natural fractures development,thus it is often treated by acidizing to create wormhole.Wormhole dissolution patterns are significantly affected by those characteristics.Hence,a dual-scale continuum model and equivalent seepage theory were used to study,the influence of in-layer heterogeneity,interlayer heterogeneity and natural fractures upon wormhole pattern and acid injection volume when break through （PVBT） were analyzed.The results show that an approximately the same optimum acid injection rate that leads minimal PVBT in different heterogeneity level do exist,and the minimal PVBT firstly increased and then decreased with the increase of heterogeneity level.High permeability zone leads to sharp decrease of PVBT ,but the inference of permeability increase on PVBT decrease becomes weak gradually when the permeability increases to a certain level.The extension direction of wormhole is decided by natural fractures when acid flows into it,and the PVBT decreased sharply by the fractures which are parallel to the acid flow direction.With the increase of fracture length,the acid injection volume tends to decrease linearly.The study is of great significance in guiding matrix acidizing of carbonate reservoirs.