A proppant mechanical model in postfrac flowback treatment

• Different proppant mechanical models are built before and after fracture closure.
• Gradually increasing flowback velocity can keep proppant in fracture as much as possible.
• Reducing the viscosity of fracturing fluid for gel breaking can improve postfrac flowback results.

It is well known that proppant back flow is a key evaluation criterion in postfrac flowback treatments. Based on the analysis of the physical processes of proppant flowback, a proppant mechanical model is established, the model considers different stress situations before and after fracture closure. Through calculation and analysis, the results show that deposited proppant are carried difficultly and suspended proppant are carried easily before fracture closure. When fracture close down, the cementations of particles become closer and critical velocity become bigger. The viscosity of fracturing fluid for gel breaking directly affects flowback procedure, the bigger viscosity is, the smaller critical velocity is and proppant are easily flowed back. Reducing the viscosity of fracturing fluid for gel breaking, adopting a lower velocity before fracture closure and a higher velocity after fracture closure, cannot only carry fracturing fluid away from formation as soon as possible, but guarantee for the keeping proppant in fracture as much as possible. These results enrich the theories of postfrac proppant flowback.