Abstract: Within the ongoing effort towards a better understanding of the influence of the stress shadow on the choice of fracture spacing in alternative fracturing, an optimised particle flow theory of fluid-solid coupling was applied to simulate the distribution of the induced stress due to the stress shadow around double hydraulic fractures. Numerical results were compared with the theoretical analysis solution to verify its rationality. Numerical simulations under different anisotropic stress fields and initial hydraulic fracture spacing were carried out to investigate the effect of the stress shadow on the initiation pressure and extension forms of the induced fracture with double hydraulic fractures. Experimental results showed that the anisotropic stress field did not change the stress field around the fractures and also did not affect the initiation pressure of the induced fracture. With the decrease of initial hydraulic fracture spacing, the stress shadow effect was enhanced, and the initiation pressure of induced fracture was also increased. Both of the anisotropic stress field and initial hydraulic fracture spacing affected the extension forms of the induced fracture. With the increase of initial hydraulic fracture spacing or the hydraulic differential stress, the influence of stress shadow on the extension direction of new hydraulic fractures gradually weakened. The initial hydraulic fractures exhibit a limitation on the extension direction of the induced fracture, to some extent, which was not conducive to the formation of a complex fracture network. Based on the above results, the optimisation of fracturing spacing in alternate fracturing was qualitatively discussed.

Key words: alternative fracturing, stress shadow, fluid-solid coupling, hydraulic fracture, initiation pressure, extension forms