Proppant transport in foam fracturing fluid during hydraulic fracturing

During hydraulic fracturing treatments, proppants often settle at the fracture bottom in low viscosity fracturing fluid (e.g., slickwater) and leave a large fraction of the fractured surface unpropped. Severe proppant settling leads to under performance of the well productivity. Polymer-free foams can be used as fracturing fluids for improved transport of proppants after a low viscosity pad. In this paper, proppant transport in foam is studied during hydraulic fracturing. A proppant settling velocity correlation in foam-based fracturing fluid is developed based on laboratory-scale experiments. Foam quality and the foam velocity gradient are found to control proppant settling. Additionally, foam liquid drainage is found to be an important process affecting proppant transport, and a foam drainage model is proposed based on literature studies. The new settling velocity correlation and the foam drainage model are incorporated into an in-house fracturing simulator, and proppant placement in foam fracturing fluid is evaluated at the field-scale. Foams place proppants more uniformly than slickwater. For dry foams, drainage has little effect on the final proppant placement. For wet foams, drainage affects the final proppant distribution. The faster the foam drains, the less uniform is the final proppant placement. The liquid from the foam collects at the bottom where the proppants settle fast and form a small proppant bed.