Summary
High-quality CO2-foam fracturing has recently become a very popular stimulation tool. Dynamic fluid-loss measurements were performed on a broad range of core samples to measure the effect of several parameters on CO2-foam fluid-loss coefficients. The parameters tested were core permeability, foam quality, gelling-agent concentration in the aqueous phase, and core temperature. Measurements were performed in a recirculating fluid-flow test loop.
A variation of one order of magnitude in CIII for two-orders-of-magnitude change in permeability was observed from 0.02 to 10 md. For permeability below 1 md, foam quality had no effect. Fluid-loss control improved as gelling agent concentration in the liquid phase increased. CIII increased with increasing temperature as a result of temperature thinning of the aqueous phase.
Passage of CO2 foams through porous media caused a significant modification in quality from the input to the effluent fluid. The ratio of liquid to gas passing through the core was measured as a function of core permeability, quality, and gelling-agent concentration. In low-permeability cores, flow proceeded as separate phases, whereas in higher-permeability cores, the foam structure remained more nearly intact.
CO2 foams were found to be very similar to N2 foams with respect to the above parameters.