Unified Model for Steady-State Foam Behavior at High and Low Foam Qualities

Abstract

Summary Foams are routinely used worldwide to divert acid in well-stimulation treatments, and to divert gas flow in improved oil recovery (IOR) projects on a pilot basis. The complexity of foam behavior and the apparent contradictions among foam studies have bedeviled attempts to understand foams and to design effective field treatments. In 1992, Osterloh and Jante1 identified two distinct foam-flow regimes: a high-quality (dry) regime, in which the steady-state pressure gradient is independent of the gas flow rate, and a low-quality (wet) regime, in which the pressure gradient is independent of the liquid flow rate. New data for strong foams in a variety of porous media, with various surfactant formulations, and over a range of flow rates, show this behavior to be general. In each regime, foam behavior is dominated by a single mechanism: at high qualities by capillary pressure and coalescence, and at low qualities by bubble trapping and mobilization. Based on these insights, a new, unified model unites foam behavior in acid-well stimulation and gasdiversion IOR and reconciles apparently contradictory data. This model correlates the effects of parameters, such as rock permeability and surfactant formulation, on foam behavior in the two flow regimes and on the transition between the two regimes. A variety of laboratory data supports the model's assumptions. The implications of these results for designing foam processes for IOR and acid diversion are discussed. These insights can guide the selection of foam formulation and injection quality for foam applications.