Migration and distribution laws of proppant in multi-scale fractures during deep shale fracturing

The developed natural fractures and bedding fractures in deep shale facilitates the formation of the multi-scale fracture structure composed of main fractures, branch fractures and secondary microfractures after volumetric fracturing, but influenced by high vertical stress and horizontal stress difference, the apertures of the hydraulic fractures in deep shale are extremely small and the aperture difference between main fractures and secondary fractures is large. In order to figure out the migration mechanisms and distribution laws of proppant in multi-scale fractures, this paper establishes a large visual experiment system of proppant transport, and studies the influence laws of pumping displacement, liquid viscosity, proppant particle size, proppant concentration and fracture characteristics parameter on proppant migration and distribution. Finally, based on the water-electricity similarity principle, the overall fracture conductivity is calculated, evaluated and analyzed. And the following research results are obtained. First, the proppant in fractures accumulates in many modes, which is controlled by the proppant carrying capacity of fluid. Second, the proppant diverting efficiency is under the influence of multiple factors, and can be improved by increasing the displacement or decreasing the proppant particle size. Third, in multi-scale fractures, the non-uniform distribution of proppant can be improved to some extent by increasing the displacement or the fracturing fluid viscosity, but the fracture conductivity increases first and then decreases. Fourth, based on the proppant diverting results and the proppant distribution laws in multi-fractures comprehensively, it is recommended to follow the idea of large displacement & low viscosity pumping to ensure the proportion of large-particle size proppant with an appropriate amount of small-particle size proppant, so that a high-conductivity fracture body of high conductivity near the wellbore & support far from the wellbore is formed. In conclusion, the proppant migration and accumulation modes under different conditions are studied comprehensively and systematically using the large visual experiment system of proppant transport in multi-scale fractures. The research results can provide a theoretical support for the design and optimization of the pumping parameters in deep shale fracturing. © 2024 Natural Gas Industry Journal Agency. All rights reserved.