碳酸盐岩储层天然微裂缝一般较为发育,很多学者在对碳酸盐岩酸蚀蚓孔扩展进行模拟研究时,都未考虑微裂缝的分布及产状的随机性对模拟结果的影响。天然微裂缝的存在对孔隙度的改变非常小,但其对于模拟结果的影响很大。基于双重尺度蚓孔扩展模型,耦合Monte Carlo法产生的具有一定统计学分布规律的天然裂缝模型,建立考虑天然微裂缝存在的酸蚀蚓孔扩展数学模型。通过改变微裂缝方位角、微裂缝密度、微裂缝长度、微裂缝连通性等参数,研究了天然微裂缝的空间分布对蚓孔扩展的影响。研究发现,天然微裂缝的存在会降低酸液突破岩心孔隙体积,很大程度上影响了最佳注入速度与酸液用量的选择。高密度的天然微裂缝可以形成复杂的弥散性裂缝网络,起到增渗、增产的效果。增加微裂缝长度可以降低酸液突破孔隙体积,对污染带进行快速穿透。在微裂缝连通性较好的岩心中,蚓孔在扩展过程中会连通相邻微裂缝,增加岩心的导流能力。

Natural micro-fractures in carbonate reservoirs are generally developed and have little effect on porosity, but has a great influence on the simulation results. In previous studies, the effect of micro-fractures on the growth of wormholes has not been studied in detail. Based on the double-scale wormhole propagation model, and the natural fracture model with a certain statistical distribution law produced by coupling of the Monte Carlo method, the acid wormhole propagation mathematical model considering the existing of natural fractures is established. By adjusting the parameters such as azimuth, density, length and connectivity of micro-fractures, the effects of its spatial distribution on wormhole propagation is studied. It is found that the existence of natural micro-fractures will reduce the pore volume of acid invasion into the cores, which greatly affects the optimal injection speed and acid-liquid dosage. Natural micro-fractures with high density can form complex dispersion fracture networks, increasing the permeability and production obviously. Increasing the length of micro-fractures can reduce the pore volume of acid invasion, and penetrate the damage zone rapidly. In the cores contain micro-fractures with better conductivity, the wormhole will connect the adjacent micro-fractures in the process of propagation, so as to increase the core's conductivity.