Modeling polymer displacement in hydraulic fractures at the pore-scale

Document Type

Conference Proceeding

Publication Date

12-1-2004

Abstract

Proppant-packed fractures provide a relatively low-resistance pathway for the recovery of reservoir fluids. However, residual polymer left over from the proppant transport can greatly reduce the fracture conductivity and, therefore, productivity. Poor fracture cleanup is often observed and it is important to understand the fundamental reasons behind the phenomenon. It is believed that non-Newtonian fluid rheology, viscous fingering, and leak off may all contribute to the problem. The vast majority of fracture cleanup modeling has been limited to continuum-scale modeling. However, important aspects of the cleanup problem may be affected by pore-scale events. For this reason, it is desired to model flow at the pore-scale to obtain a better understanding of the qualitative fingering patterns and quantitative flowrates in a fracture during the cleanup process, as a function of basic parameters such as proppant size, fluid rheology, and imposed pressure gradients. These pore-scale results may help explain the fundamental reasons for the observed poor polymer cleanup and give insight on how to improve cleanup in the future. In this work, computer-generated, random sphere-packs are used to approximate a small portion of the propped fracture. The sphere-packs are transformed into physically representative networks of pores and connecting throats. The network models are used to model flow through the proppant pack at the pore-scale. Modeling the dynamic cleanup process consists simulating a low-viscosity, Newtonian fluid (e.g. water) displacing a high-viscosity, non-Newtonian polymer from the pack. A novel approach is used to couple the network to a continuum model for flow in the reservoir, and realistic boundary conditions are used that allow the displacing fluid to flow in from the side of the fracture. Current modeling is used to better understand displacement behavior under different conditions. Future results will be upscaled and integrated with large-scale reservoir models. Copyright 2004, Society of Petroleum Engineers Inc.

Publication Source (Journal or Book title)

Proceedings - SPE Annual Technical Conference and Exhibition

First Page

1751

Last Page

1766

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