Numerical simulation study of proppant transport in complex hydraulic fractures

Abstract

During the hydraulic fracturing construction of unconventional reservoirs， hydraulic fractures easily intersect with natural fractures to form complex fractures. The migration and the laying form of the proppant directly determine the stimulation effect of the reservoirs. In order to study the laying rules of proppants in complex fractures， a proppant-fracturing fluid two-phase flow mathematical model was established based on the Euler-Euler method， and the dune laying shapes in complex fractures of the indoor test device and the numerical simulation were compared to verify the model. The results show that the selected Euler two-fluid numerical model can be used to study the migration and laying rules of proppants carried by slick water in complex fractures. Based on the similarity criterion， a simplified complex fracture plate model was established， and the morphological parameters and area of the dune were normalized to obtain the influence of the fracturing fluid displacement， viscosity， proppant particle size， fracture width， and fracture morphology on proppant laying in complex fractures. The results show that increasing the displacement and viscosity and reducing the particle size is beneficial to proppant migration to the depth of the fractures， and the displacement has the most obvious impact on the shape of the dune in the branch fractures， but increasing the displacement is not conducive to proppant to fill the near-well zone. The influence of the fracture width is reflected in the wall effect. Under the same injection time， when the viscosity of the fracturing fluid increases from 1 mPa·s to 5 mPa·s， the normalized length of the main fracture dune increases by 37.9% on average， and the normalized height reduces by 61.4%. A more complex fracture structure indicates a higher proportion of proppant laying area in all branch fractures and a more significant diversion effect. As the number， series， and extension length of the branch fractures of complex fractures increase， the height and length of the dune in the branch fractures decrease； compared with the T1 type fracture， the dune in the T3 and T5 type fractures decreases the most in terms of length and height.

Keywords

• hydraulic fractures
• slick water fracturing
• two-fluid numerical model
• proppant
• normalization