Towards Proppant Back-Production Prediction

Abstract Proppant back-production from hydraulically fractured wells is a great operational problem to the oil and gas industry. Apart from safety problems related to erosion of tubing and valves, extra equipment and operators are required to handle wells that produce proppant. Substantial work has been conducted to develop methods to control proppant back-production. The methods include the modification of completion designs, the use of controlled fracture closure to obtain early closure on the proppant and the use of new materials designed to prevent proppant production. These materials include curable resin coated proppant, fiberglass, thermoplastic filmstrips, and chemicals that modify the surface of the proppant. Relatively little effort, however, has been directed towards understanding the mechanisms that cause proppant back production. A review of the relevant literature shows some experimental studies at a laboratory scale and one numerical study on the mechanical stability of proppant packs. This paper presents the results of combined experimental and modelling studies to quantify parameters critical to proppant back-production. Laboratory experiments were conducted in several slot flow models. The experimental results were used to calibrate a numerical model to predict back-production. In the model flow inside the proppant pack is described by Darcy's equation for flow through porous media. The resulting velocity distribution is used to assess the local stability along the free surface between the proppant pack and the continuous fluid phase. These steps are repeated to evaluate the development of the interface over time. Similar methods have been used to describe viscous fingering in petroleum reservoir engineering. However, in viscous fingering the interface moves in the same direction as the fluid while the directions are opposite in the application described here. Example simulations show how stable open channels can develop in propped hydraulic fractures. The results provide a foundation for the existence of such channels as has been speculated and hypothesized by many people over the last couple of years.