Increasing the efficiency of completions in horizontal wells is an important concern in the oil and gas industry. To decrease the number of fracturing stages per well it is common practice to use multiple clusters per stage. This is done with the hope that most of the clusters in the stage will be effectively stimulated. Diagnostic evidence, however, suggests that in many cases only 1 or 2 clusters out of 4 or 5 clusters in a stage are effectively stimulated.

In this paper strategies to maximize the number of effectively stimulated perforation clusters are discussed. A fully 3-D poroelastic model that simulates the propagation of non-planar fractures in heterogeneous media is developed and used to model the propagation of multiple competing, fractures. A parametric study is first conducted to show how important fracture design variables such as limited entry perforations and cluster spacing; and formation parameters such as permeability, lateral and verical heterogeneity affect the growth of competing fractures. The effect of stress shadowing due to both mechanical and poroelastic effects is accounted for.

3-D numerical simulations have been performed to show the impact of some operational and reservoir parameters on simultaneous competitive fracture propagation. It was found that an increase in stage spacing decreases the stress interference between propagating fractures and increases the number of propagating fractures in a stage. It was also found that an increase in reservoir permeability can decrease the stress interference between propagating fractures because of poro-elastic stress changes. A modest (about 25%) variability in reservoir mechanical properties along the wellbore is shown to be enough to alter the number of fractures created in a hydraulic fracturing stage and mask the effects of stress shadowing. Inter-stage fracture simulations show post-shutin fracture extension induced by stress interference from adjacent propagating fractures. The impact of poro-elasticity is highlighted for infill well fracture design and preferential fracture propagation towards depleted regions is clearly observed in multi-well pad fracture simulations.

The results in this paper attempt to provide practitioners with a better understanding of multi-cluster fracturing dynamics. Based on these findings recommendations are made on how best to design fracture treatments that will not only lead to the successful placement of fluid and proppant in a single fracture, but in a set of fractures that are competing with each other for growth. The ability to successfully stimulate all perforation clusters is shown to be a function of key fracture design parameters.

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