Rheological Study of Foam Fracturing Fluids Using Nitrogen and Carbon Dioxide

Summary A practical mathematical model based on experimental data is presented for calculation of rheological properties of N2 and CO2 foam stimulation fluids. The laminar flow model is a yield pseudoplastic type, with viscosity dependent on foam quality, yield point, base liquid consistency index (K′), and flow behavior index (n′). Turbulent foam flow data were analyzed with API RP39 procedures but were modified to include variable density effects of foam fluids. Water-based foam apparent viscosities compare closely to Mitchell's Bingham plastic model at high shear rates. The yield pseudoplastic model also includes viscous effects of gelling agents and measurement at much lower shear rates. Comparison of predicted pipe friction was made to actual field wellhead pressures with good agreement.