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.