关键词: 页岩, 层理, 离散元, 裂缝扩展, 流固耦合, 多簇裂缝

Abstract: The bedding of the Longmaxi Formation shale in Changning is developed,and the fracture height is limited during hydraulic fracturing,which is not conducive to connecting with high-quality “sweet spots” and reduces the effective seepage range,thereby affecting the hydraulic fracturing effect.In response to the above issues,based on the discrete element method of particle flow and considering the fluid-solid coupling effect,a simulation model for the coupling of horizontal section clustered perforating,bedding fractures, and fracture propagation in bedded shale was established.The model was used to simulate and analyze the fracture height propagation law.The field application results are consistent with the model simulation results.The study shows that bedding has a strong inhibitory effect on the fracture height propagation of shale fracturing,and the presence of bedding fractures causes the fracture height to deviate from the vertical extension.When the tensile strength of the bedding fractures is low,the fractures are more likely to activate and propagate along the bedding fractures,resulting in a relatively smaller fracture height.The difference between the vertical stress and the minimum horizontal principal stress has a much greater impact on fracture height propagation than the Young′s modulus and Poisson′s ratio.Under low stress difference, the fractures almost propagate along the bedding direction,and the fracture height is greatly restricted.The clustered perforating parameters and the amount of fracturing fluid have a relatively greater impact on fracture height.It is recommended to use a low viscosity (50 mPa·s),high flow rate (18 m³/min),and large volume (2 000 m³) method for volumetric fracturing.The recommended number of perforation clusters is 6,with a cluster spacing of 12 m.After fracturing,the test well has good vertical extension and a large fracture volume,with a tested daily gas production of 21.5×10⁴ m³.The research results can provide a reference for the stimulation of similar shale reservoirs.

Key words: shale, bedding, discrete element, fracture propagation, fluid-solid coupling, multi-cluster fracture