Polymers for Mobility Control in CO2 Floods

Abstract

ABSTRACT The very low viscosity of the displacing fluid is the probable cause of much of the early breakthrough and poor areal sweep efficiency that plagues most applications of CO2 flooding technology. A focussed and already partially successful research program is described, to develop polymers that are soluble in dense CO2 and raise its viscosity sufficiently so that they can be used as direct thickeners for mobility control. Such water-free additives will offer greatly improved displacement efficiencies on both microscopic and macroscopic scales. Developed correlations between molecular structure and solubility in both simple hydrocarbon-CO2 and in polymer-CO2 systems are reviewed. Guided by these, we have synthesized amorphous poly-1-hexenes as a first step towards the preparation of more complex multicomponent polymer systems. Reported in this paper are results on the solubilities and viscosities of various α-olefin polymers in dense lower hydrocarbons such as n-butane and n-propane, which are close to dense CO2 in many solvent properties. Also reported are other experimental details, including the development of gas chromatographic techniques to follow the course of higher α-olefin polymerization, and measurements of molecular weights and molecular weight distribution of the synthesized polymers. It is pointed out that polymers of narrow molecular weight distribution must be used for accurate determination of solubilities in dense CO2.