Mechanistic Studies of Improved Foam Eor Processes

Abstract

The objective of this research is to widen the application of foam to enhanced oil recovery (EOR) by investigating fundamental mechanisms of foams in porous media. This research is to lay the groundwork for more-applied research on foams for improved sweep efficiency in miscible gas, steam and surfactant-based EOR. Task 1 investigates the pore-scale interactions between foam bubbles and polymer molecules. Task 2 examines the mechanisms of gas trapping, and interaction between gas trapping and foam effectiveness. Task 3 investigates mechanisms of foam generation in porous media.For Task 1, we investigated the interactions of polymers and foam in search of means to stabilize and strengthen foam using polymers, especially in the presence of oil For the polymers (xanthan and partially hydrolyzed polyacrylamide), oils (decane and 37.5° API crude oil), and surfactant (alpha-olefin sulfonate) tested here, it appears from coreflood pressure gradient |∇p| that polymer destabilizes foam modestly, raising water saturation S w and water relative permeability k rw . The increased viscosity of the aqueous phase with polymer partially compensates for the destabilization of foam. For the same polymers and surfactant, polymer does not stabilize foam in the presence of decane or 37.5° API crude oil.Complex behavior, in contradiction to the expected two steady-state strong-foam regimes, was sometimes observed. At the limit of, or in the place of, the high-quality regime, there was sometimes an abrupt jump upwards in |∇p| as though from hysteresis and a change of state. In the low-quality regime, |∇p| was not independent of liquid superficial velocity, but decreased with increasing liquid superficial velocity. This curious behavior in the low-quality regime was also found in studies of CO 2 foam; an explanation was discovered in research on Task 2. Pressure gradient can decrease upon increasing liquid superficial velocity in the low-quality regime because the drag on bubbles decreases as the liquid film between the bubble and the pore wall thickens.A new theory developed for the drag on bubbles moving through tubes suggests that polymer should make foam more shear-thinning than foam without polymer, both in the high-quality and low-quality flow regimes.Regarding Task 2, a new model for gas trapping was incorporated into a foam simulator. In this model, trapped-gas saturation is a function of pressure gradient, fit to DE-FC26-01BC15318 Final Report -4 data for liquid relative permeability following foam injection and the gas relativepermeability curve. This model can fit steady-state data for the two strong-foam flow regimes and in limited trials it also fitted the transition period between foam injection and injection of liquid following foam in coreflood experiments. The simulator would be most helpful in modeling liquid injectivity in SAG foam processes.Coreflood experiments during liquid injection following foam concluded that liquid saturation rose more upon liquid injection; i.e., less gas was trapped during liquid inj...