Abstract: At present,the horizontal drilling with large-scale hydraulic fracturing is the main technology to mine shale gas while volumetric fracturing would induce cracks underground and communicate natural cracks to form complex fracture networks eventually. In order to simulate the seepage flow of shale gas in the complex fracture network and characterize the network on the shale gas model,a random fractal network model was established through a two-porosity component simulator combined with the random fractal geometry system. Based on the above model,five schemes for carbon dioxide stimulation to extract shale gas were further studied. The results show that CO₂ huff and puff can significantly increase the production of shale gas,and the increase of injection pressure and injection time can improve the ultimate recovery. The latter has the optimal value in the process of shale gas production,and too early or too late injection timing will make the production worse,and there is an optimal injection timing range in each CO₂ injection cycle. The fractal fracture network model provides a theoretical basis for further research on the simulation of fracture CO₂ huff and puff production of shale gas reservoir.

Key words: shale gas, volumetric fracturing, fractal geometry, CO₂ huff and puff, numerical simulation