However, in unconventional shale reservoirs, the large polymer molecules can plug the small pores of the fracture surface and decrease the gas flow (Peles et al., 2002). The second way is to use foam-based fracturing fluids (Gidley et al., 1990). The cellular structure of foams can give a high effective viscosity without plugging up the shale pores if polymers are avoided. Foams are usually generated from a base fluid made from a surfactant, a polymer stabilizer such as guar, HPG, and Xanthan gums. Foams made from a surfactant foamer without polymers are known as polymer-free (or gel-free) aqueous foams. The foam rheology is a very important property for fracture-treatment design. It influences the tubing pressure drops, pump pressure head, fracture geometry, proppant transport and fluid loss to the matrix. It is affected by foam quality, texture, viscosity of the base aqueous phase, pressure and temperature. A circulating loop rheometer is widely used to characterize the foam rheology.