基于实验方法的酸压裂缝分形研究

Experimental study on fractal characteristics of fractures in acidizing fracturing process

酸压是提高碳酸盐岩储层渗透率的主要措施,酸压裂缝的形成和延伸直接影响到油气井产能。为此,采用分形方法研究酸压过程中裂缝的形成和延伸机理。首先推导出裂缝导流能力与裂缝分形维数之间的函数关系,然后采用造缝后的岩心进行一次酸压和重复酸压实验,测试酸压前后裂缝导流能力的变化,得到一次酸压和重复酸压前后裂缝的分形特征变化。研究表明:酸压裂缝的几何形态及分布具有明显的分形特征,其中一次酸压以酸蚀原始裂缝、促进原始裂缝延伸为主,酸压前后裂缝分形维数明显降低;重复酸压以造新裂缝为主,分形维数较一次酸压明显提高。

Acidizing fracturing is one of the major measures of enhancing the permeability of carbonate reservoir. For this reason, the forming and growth mechanism of fractures in the acidizing fracturing process is studied using fractal method. Firstly,the relationship between the fracture flow capacity and fractal dimension is derived,and then,the fractal dimensions of fractures before and after the first acidizing fracturing and the second acidizing fracturing are obtained by testing fracture flow capacity. The fractal characteristics of fractures in the first acidizing fracturing and the second acidizing fracturing are studied according to the change of the fractal dimension of fractures before and after acidizing fracturing. It is shown that,the geometrical morphology and size distribution of acidizing fracturing fractures have obvious fractal feature; the fractal dimension of fractures decreases after the first acidizing fracturing,so the effect of the first acidizing fracturing is mainly the acid corrosion and growth of original fractures; the fractal dimension of fractures increases after the second acidizing fracturing,so the effect of the second acidizing fracturing is mainly generating new fractures.