THEORY OF MOBILIZATION PRESSURE-GRADIENT OF FLOWING FOAMS IN POROUS-MEDIA .1. INCOMPRESSIBLE FOAM

A theory is presented for the minimum pressure gradient (∇p)min required to keep a foam flowing through a porous medium. The theory accounts for pore shape, foam texture, contact-angle hysteresis, and bubble separation at pore throats, but not for the effects of gas compressibility or of the Plateau borders where liquid lamellae contact the pore wall. Quantitative estimates of (∇p)min depend on pore shape, foam texture, and surface tension. For medium-textured foams (bubbles 400 μm in diameter in bulk), reasonable parameter values give (∇p)min = 18-32 kPa/m (0.8-1.4 psi/ft) for CO2 foams and 125-240 kPa/m (5-11 psi/ft) for others foams. Lower gas/liquid surface tension causes the lower estimate for CO2 foams. For most foams, foam texture must coarsen substantially as foam flows away from the well in oilfield application, or formation plugging results. Further, to flow at 20-45 kPa/m (1-2 psi/ft), foam bubbles must be at least 1 or more cm, or hundreds of pores, in length. CO2 foams, on the other hand, can still flow if bubbles are somewhat smaller. The highest values of (∇p)min are predicted for foams in pores with high aspect ratio (body radius/throat radius), sharp corners, and narrow throats, and at low capillary pressures (wet foams). © 1990.