Effects of Texture on Rheology of Foam Fracturing Fluids

Summary A new laboratory technique was developed to measure changes in foam texture (bubble-size distribution) vs. foam viscosity in a recirculating pipeline viscometer. Fluid variables studied included foam quality, surfactant type and concentration, gelling-agent concentration, shear history, system pressure, and liquid-phase chemical type. The viscous properties of foam fluids are determined primarily by quality (internal-phase volume) and liquid-phase properties. The viscosity of an equilibrated foam is influenced by texture to a lesser extent. Foams are shear-history-dependent fluids. The bubble size and degree of dispersion will adjust to an equilibrium state that depends on time at a given shear rate. Finer-texture foams are produced by higher shear rates, higher surfactant concentrations, and higher pressures. Viscosity measurements at low pressure may not adequately simulate field use at high pressure. The liquid-phase chemical type influences texture. The structure of methanol and hydrocarbon foams may result in sensitivity to degradation at high shear rates.