CFD Modeling of Proppant Transport in Tight Gas Fractures and Strategies for Production

Enhancements

Hydraulically stimulated fractures in unconventional oil and gas reservoirs require the presence of proppants to maintain their conductivity for optimized oil and gas production. The proppants are injected into the stimulated reservoir fractures with either water or gel, a highly viscous fluid modified by specially cross-linked polymers. The gel liquid can be designed to have certain viscosity values in order to place proppants at desired pump rate to form desired distribution pattern. Although the interaction process between the carrier liquid can proppants can be studied in labs, the limitation of lab scale severely hinders the understanding of the proppant transport process in a real fracture.
This work extends our previous efforts on the development of CFD modeling for dense phase slurry flows (Tsai et al., 2012; Tsai, 2013) to model the full scale of the stimulated fractures in unconventional tight gas reservoirs. The use of an efficient hybrid Lagrangian/Eulerian method (Snider, 2001) enables the modeling of dense phase slurry flows approaching the packing limits. The inter-particle collision model adopted by Snider (2001) enables the efficient modeling of proppant transport in a full-scale reservoir fracture (>100â??x1000â??) for a long duration (>2 hours). However, the inter-particle collision model requires some adjustment to reproduce the lab results (Sahai et al., 2014). Although our earlier efforts showed the model can be used to mimic sand transport in pipes, the larger scale requires more sophisticated collision models to account for the sand settling and re-entrainment behavior.
The application to proppant distribution in a fracture under various scenarios, including various pumping schedules and gel viscosities, will be presented and discussed. The possible influence to the oil and gas production rate will also be addressed.

References

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Tsai, K., â??CFD Modeling of Sand Distribution in a Multiply-Perforated Horizontal Pipe for Applications in
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flows,� J. Comp. Phys., 170, pp. 523-549, 2001
Sahai, R., J. L. Miskimins, K. E. Olson, â??Laboratory results of proppant transport in complex fracture systems,â? SPE paper 168579, SPE HFTC Conference, The Woodlands, TX, 2014.