Effect of foam quality on flow behavior of liquid CO2-based foam fracturing fluid stabilized by hydrofluoroether

Hydrofluoroether C4F9OCH3, as a foaming agent in liquid CO2, is used to stabilize bubble in liquid CO2-based foam fracturing fluid which is waterless and no damage to oil-gas reservoir. However, characteristics of this environmental friendly CO2-based foam, such as the foam morphology and its flow behaviors in pipe, are insufficiently understood. Especially, foam quality, one of important characteristic parameters in a foam fluid, has significant effects on foam structure and flow behaviors of CO2-based foam. By means of the flow tests in pipes with different diameters, it was found that the CO2-based foam displayed wall slip phenomenon, and Oldroyd-Jastrzebski method was used to deal with this phenomenon. Effective viscosity of this CO2-based foam, as well as convective heat transfer coefficient initially increases and then decreases with the increase of foam quality. Due to dominant collision and friction among bubbles, their values reach the corresponding maximums when the foam quality is about 0.82. Meanwhile, the evolution of rheological parameters of CO2-based foam with the foam quality is shown as well, and the exponential relationship between yield stress and foam quality is illustrated. Additionally, as for the flow friction characteristics, it shows that fanning friction factor increases and drag reduction rate initially increases and then decreases as the foam quality is increased.