Polymer-Enhanced Foams Part 1: Laboratory Development And Evaluation

Abstract

SUMMARY A laboratory study was conducted to identify pertinent properties and features of polymer-enhanced foams (PEFs). In addition, initial development of acrylamide-polymer oil-recovery PEFs was completed. Polymer addition to the aqueous phase of conventional foams resulted in foams of enhanced viscosity and stability. Based on findings of this laboratory study, PEFs appear to be attractive conformance-improvement fluids and attractive mobility-control fluids for use in naturally fractured reservoirs. The acrylamide-polymer PEFs promoted exceptionally high effective viscosities and were much more stable than conventional oil-recovery foams. Effective viscosities of the PEFs were comparable to the viscosities of the polymer solutions from which the PEFs were derived. PEFs exhibited shear-thinning viscosity behavior which makes them attractive for use as mobility-control fluids. The following parameters relating to PEFs were studied: polymer properties and concentration, surfactant types and concentration, aqueous phase viscosity, absolute pressure, foam quality (volume fraction gas), gas type, stability in glassware, rheology and the effect of shear, critical pressure gradient for flow, and briefly, temperature and brine makeup chemistries. Stability of PEFs in glassware was much better than that of counterpart conventional foams. PEFs were successfully formulated over a broad range of foam qualities, and the viscosity performance of the PEFs was highly insensitive to foam quality. A PEF was more efficient than brine or two polymer solutions at displacing a viscous oil (25:1 oil:water viscosity ratio) in an ideal fracture model. Much of the experimental work involved constant-differential-pressure flooding experiments performed in high-permeability sandpacks. PEFs were successfully formulated with nitrogen, carbon dioxide, and methane as the gas phase. The study was limited to PEFs for application within fractures of naturally fractured reservoirs and to PEFs that are to be generated above-ground prior to injection. Only the addition of acrylamide polymers to foams was considered. A large majority of the PEFs were formulated with alpha olefin sulfonates as the foaming surfactant.