Abstract
As foam is injected into an oil reservoir, the region near an injector can become oil-free due to the relatively high capillary number. Foam created in this region encounters oil further out in the reservoir. The impact of oil on foam in porous media is usually investigated by co-injecting surfactant, gas and oil, or by injecting pre-generated foam into an oil-saturated core. However, the former experiment does not give information on the impact of oil on pre-generated foam, and with the latter experiment one cannot easily obtain data at different oil fractional flows, necessary to model the impact of oil on pre-generated foam.
Here we present a novel but relatively simple experimental technique for investigating the effect of oil on pre-generated foam in porous media. This allows one to compare the effects of oil on pre-generated foam and on foam generation without the experimental complications involved in using two separate porous media. We co-inject surfactant solution and gas into a relative narrow core (1 cm diameter), and inject oil into the core some distance downstream from the inlet through ports in the side of the core. The relatively narrow core allows rapid contact between the injected crude oil and pre-generated foam in a porous medium much larger than pore dimensions. By injecting the three phases into the core we investigate the flow behaviour of foam with oil at fixed fractional flows of all three phases.
We illustrate the technique with a study of the effect of one crude oil with two surfactants. With this system, there is a progressive decrease in the apparent viscosity of the foam after encountering oil. Foams with a higher gas fraction experiences a more-significant weakening by oil over the length of the core than foams with a lower gas fraction. By the end of the core, the apparent viscosities of foam with a higher gas fraction approach values observed with three-phase co-injection. We present a novel, but relatively simple method to investigate the change of foam mobility as it encounters oil in a porous medium, at controlled fractional flows. We show that in our case the apparent viscosity of foam with oil can decrease by more than a factor of four over a distance of 15 cm, indicating that foam and oil reach steady-state (as observed with three-phase co-injection) almost instantaneously compared to the length of a reservoir-simulation grid-block.
•Novel experimental approach to investigate the impact of oil on pre-generated foam.•Pre-generated foam progressively weakened in presence of oil after first contact.•The apparent viscosity in some cases decreased by more than a factor 4 over 0.15 m.•Lower-quality foams propagated for a longer distance in the presence of oil.•Foam made with pre-equilibrated surfactant collapsed more quickly on contact with oil.