Rheological behavior of aqueous foams at high pressure

Abstract

Aqueous foams are used in many oil field applications including drilling, fracturing, and enhanced oil recovery operations. The success of all these operations strongly depends on viscosity and stability of foam. Rheology of foams is a function of foam quality (i.e. gas volume fraction), liquid phase viscosity, pressure, and temperature. Besides, foam generation method and stability are factors that influence its rheology.This article presents results of an experimental study performed to investigate the effects of foam quality, pressure, and wall slip on aqueous-foam rheology. Extensive tests were conducted using a foam recirculating flow loop consisting of three pipe viscometers. Experiments were performed at ambient temperature, and varying pressure (6.89–20.68 MPa), foam quality (40–80%), and pipe diameter (3.06, 6.22 and 12.67 mm). The foam was generated by passing a mixture of water containing 2% surfactant solution and gas phase (nitrogen) through a needle valve. To minimize degradation while testing, the foam was regenerated by circulating at the maximum flow rate (0.55 L/min) before each flow measurement was made.Results indicate strong non-Newtonian behavior of foam, which closely fits the power law model. For foams with more than 55% quality, measured viscosities were higher than the ones reported in the literature. Noticeable wall slip was not observed. Foam viscosity change because of pressure variation at a constant foam quality was negligible. Foams with quality higher than 70% exhibited yield pseudoplastic behavior. Their rheological behavior can be described better by Herschel–Bulkley model than power law model when the shear rate is below 20 1/s.