Experimental and simulation study of foam in porous media

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Date

2006

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Shen, Chun

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This dissertation comprises two studies of foam in porous media. The first part is an experimental study of the effect of polymer on the properties of foam in porous media. Addition of polymer has been proposed as a way to stabilize foam, especially in the presence of oil. This study probes the possible stabilizing effect of polymer on foam in terms of steady-state properties. Specifically, we tested the effect of polymer addition on the two steady-state foam regimes identified by Alvarez et al. (2001). For the two polymers (Xanthan and partially hydrolyzed polyacrylamide), two oils (decane and 37.5°API crude oil), and surfactant (an alpha-olefin sulfonate surfactant (AOS)) tested, it appears from coreflood pressure gradient that polymer destabilizes foam modestly. The increased viscosity of the aqueous phase with polymer mitigates the effects of 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 relative to foam without polymer. Surface-tension measurements with these polymers and surfactant likewise showed no evidence of presence of polymer at the air-water interface that might stabilize foam lamellae between bubbles. This suggests that, for similar polymers and surfactants, addition of polymer would not give stronger foams in field application or stabilize foam against the presence of crude oil. Complex behavior, some of it in contradiction to the expected two steady-state foam regimes, was observed. At the limit of, or in the place of, the high-quality regime, there was sometimes an abrupt jump upwards in pressure gradient as though from hysteresis and a change of state. In the low-quality regime, the pressure gradient was not independent of liquid superficial velocity, but decreased with increasing liquid superficial velocity, as previously reported and explained by Kim et al. (2004). The second part of this dissertation is a simulation study of gravity segregation during injection of shear-thinning foam in a homogenous reservoir. A useful model for gravity override with Newtonian flow is Stone’s model (1982), which describes gravity override during simultaneous water-gas flow. Shi and Rossen (1998) extend the model to foam processes with Newtonian rheology. However, foams are non-Newtonian, often in the high-quality regime, and always in the low-quality regime. In this study we examined the ability of shear-thinning foam to overcome gravity segregation in homogeneous reservoirs with different foam properties. In the limited range of conditions tested, we extended Stone's model to non-Newtonian flow using the estimated mobility at a representative "average" location which depended on the degree of shear-thinning behavior. We then developed a method to estimate the segregation distance for nonNewtonian foams that required iterative calculation but not computer simulation. The estimates were qualitatively, but not quantitatively, correct.

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