Secondary oil recovery process with incremental injection of surfactant slugs
Improved oil recovery can be obtained by the use of staged or incremental injection of at least two sulfonate-sulfate surfactant slugs, where the first slug is compatible with the connate water or water of high salinity and hardness and the last surfactant slug is compatible with the flood water. A water-thickener, such as water-soluble gums and/or polymers such as partially hydrolyzed polyacrylamides may be added to the waterflood. Each surfactant slug contains different mixtures of dissimilar surfactants of which one is an alkali metal or ammonium or amine salt of an organic sulfonate, and the other is an alkali metal or ammonium or amine salt of a sulfated oxyalkylated organic material. Where the salinity of the water is relatively high, the ratio of sulfonate to sulfate by weight should be low, and vice versa. High salinity requires an additional amount of the sulfate surfactant. Incremental injection of graded surfactant slugs eliminates the necessity of a low salt preflood, reduces the amount of water-thickener necessary for mobility control, and minimizes adsorption of the surfactants onto the formation surfaces. Hence, the amount of sacrificial additives can be minimized or eliminated. Berea cores were used to compare a one step surfactant flood process with the incremental injection of several slugs of varying composition. The incremental process produced significantly better total oil recovery.
- Assignee:
- Shell Oil Co.
- Patent Number(s):
- US 3638728
- OSTI ID:
- 7299597
- Country of Publication:
- United States
- Language:
- English
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