Improvements in and relating to miscible gas enhanced oil recovery from petroleum bearing formations

摘要

61936-1770 MISCIBLE GAS ENHANCED OIL RECOVERY METHOD USING OIL-BRINE COMPATIBLE PREFORMED FOAM Oil recovery from a petroleum reservoir using a miscible gas, such as carbon dioxide, nitrogen or methane is enhanced by injecting a preformed stable foam into the reservoir. The foam composition is formed by an alpha olefin sulfonate (AOS) having from 8 to 24 carbon atoms in water having a salt content similar to that in the reservoir and the miscible gas. In a preferred form the AOS has a carbon content of less than 12 carbon atoms in higher salt content brines and less than 12 carbon atoms in lower salt content brines. Most preferably, in brines having a salt concentration of at least 10 weight percent, the effective amount of AOS has 10 carbon atoms; in brines having a salt concentration of from 2 to 10 weight percent the AOS has 12 carbon atoms; and in brines having less than 2 weight percent salt the AOS has 14 carbon atoms.