Understanding Proppant Flowback

Abstract Proppant production from hydraulically fractured wells can cause severe operational problems, increase safety concerns, and dramatically reduce economic returns on well-stimulation investments. Methods that have helped eliminate or minimize proppant flowback include modified completion designs, the use of controlled fracture closure for obtaining early closure on the proppant pack, and the use of materials designed to reduce proppant production. Curable resin-coated proppants, chopped fiberglass, thermoplastic strips, and chemicals that modify the surface of the proppant are all accepted methods for minimizing flowback. This paper presents the results of both physical and numerical modeling of proppant flowback recorded during the development of a chemical designed for modifying the proppant surface. The goal of this study was to develop an understanding of the mechanisms that control proppant flowback. Laboratory experiments performed in slot models with no closure stress helped establish the interaction of proppant size, proppant distribution, and fluid velocity. Additional studies of the impact of closure stress, fracture width, and fluid rate on proppant flowback were performed with modified API linear conductivity cells. Data obtained from the physical modeling were used to calibrate a numerical model that predicts proppant flowback. In this model, fluid flow in the proppant pack is described by Darcy's equation for flow through porous media. The resulting velocity distribution allowed local stability to be assessed along the free surface between the proppant pack and the continuous fluid phase. Repeating these steps allowed evaluation of the interface that develops over time.