With the growing interest in low-permeability gas plays, foam fracturing fluids are now well established as a viable alternative to traditional fracturing fluids. Present practices in energized fracturing treatments remain nonetheless rudimentary in comparison to other fracturing fluid technologies because of our limited understanding of multi-phase fluid- loss and phase behavior that occurs in these complex fluids. This paper assesses the fluid-loss benefits introduced by energizing the fracturing fluid to estimate when and why energized fluids may be suitable.
A new laboratory setup has been specifically designed and built for measuring the leak-off rates for both gas and liquid phases under dynamic fluid-loss conditions. This paper provides experimental leak-off results for linear guar gels and for N2- guar foam-based fracturing fluids under a wide range of fracturing conditions. In particular, the effects of the pressure drop, the rock permeability, the fluid shear rate, the polymer concentration, and the foam quality are investigated. Analysis of dynamic leak-off results provide an understanding of the complex mechanisms of viscous invasion and filter-cake formation occurring at the pore-scale.
This study presents data supporting the superior fluid-loss behavior of foams, which exhibit minor liquid invasion and limited damage. It also shows direct measurements of the ability of the gas component to leak-off into the invaded zone, thereby increasing the gas saturation around the fracture and enhancing the gas productivity during flowback. The conclusions not only confirm but add to the findings of McGowen & Vitthal (1996) for linear gels and the findings of Harris (1985) for nitrogen foams.