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 fractur- ing treatments remain, nonetheless, rudimentary in comparison to other fracturing-fluid technologies because of our limited under- standing of multiphase fluid-loss and phase behavior occurring in these complex fluids. This paper assesses the fluid-loss benefits introduced by energizing the fracturing fluid.

A new laboratory apparatus has been specifically designed and built for measuring the leakoff rates for both gas and liquid phases under dynamic fluid-loss conditions. This paper provides experi- mental leakoff results for linear guar gels and for N2/guar foam- based fracturing fluids under a wide range of fracturing condi- tions. In particular, the effects of the rock permeability, the foam quality, and the pressure drop are investigated. Analysis of dynamic leakoff data provides an understanding of the complex mechanisms of viscous invasion and filter-cake formation occur- ring at the pore scale.

This study presents data supporting the superior fluid-loss behavior of foams, which exhibit minor liquid invasion and lim- ited damage. It also shows direct measurements of the ability of the gas component to leakoff into the invaded zone, thereby increasing the gas saturation around the fracture and enhancing the gas productivity during flowback. Our conclusions not only confirm but add to the findings of McGowen and Vitthal (1996a, b) for linear gels and the findings of Harris (1985) for nitrogen foams.