Proppant placement plays a crucial role in ensuring that the conductivity of fractures is maintained after a hydraulic fracturing treatment. The process involves the transport of solids suspended in a liquid (usually a water-based fluid) from the wellbore through the perforations and finally into the fractures. Many studies have focused on proppant settling and transport in fractures but relatively few studies have investigated the transport of slurries through perforations into the fracture. The paper addresses the important issue of proppant transport through perforations by modelling the fundamental physics involved in the process. The objective of this paper is to evaluate the efficiency of proppant transport in a perforated horizontal well under different suspension flow conditions.

In this paper, proppant transport through a perforated horizontal casing is modelled using a combined CFD-DEM approach. The CFD-DEM model results are compared with experimental data and excellent agreement is observed. The effectiveness of proppant transport is evaluated by the particle transport efficiency (Ei), which is defined as the mass fraction of particles transported through the perforations relative to the total mass of particles injected. The effects of changing casing diameter, proppant size, proppant density, proppant concentration, fluid flow rate, fluid rheology, perforation size, and perforation orientation on Ei are investigated.

The results show that the perforation orientation has a large influence on Ei at low wellbore flow rates (typically seen in the downstream perforations). Under such conditions, proppant concentration in a low- side perforation is always larger than the upstream wellbore proppant concentration while proppant concentration in a high-side or a side perforation is always smaller than the upstream wellbore concentration. Increasing proppant size, proppant density, or decreasing fluid viscosity leads to an increase in Ei for low-side perforations and a decrease in Ei for high-side perforations. Increasing fluid flow rate and fluid viscosity helps to provide a more consistent Ei for perforations with different orientations; the proppant concentration in perforations in both scenarios are, however, smaller than the upstream proppant concentration regardless of perforation orientation. An increase in wellbore proppant concentration is found to have a negative effect on Ei for perforations of all orientations. An increase in perforation size is found to increase Ei for low-side and side perforations at a low flow rate but shows an insignificant effect on Ei for a high-side perforation. Finally, the usage of cross-linked gel provides a more consistent Ei among differently oriented perforations. However, even when gel is used, the proppant concentration in the perforation is still lower than the wellbore concentration, and it decreases as the flow rate increases.

Results from this paper enhance our understanding of proppant transport from the wellbore into fractures and provide guidelines for engineers to follow to better control proppant distribution in perforation clusters in horizontal wells.

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