Paper: Technical and Economic Criteria for selecting Methods and Materials for Enhanced Oil Recovery (or Why CO2 Fills the Bill in the Permian Basin of New Mexico and Texas)

Enhanced oil recovery may be defined as any combination of methods and materials which recovers oil more effectively than either plain waterflooding or gas injection. The three basic mechanisms which can be used (individually or in combination) to achieve increased recovery are to: (1) lower interfacial tension between oil and water; (2) use a solvent to extract oil; and (3) reduce viscosity contrast between the oil and displacing fluid by thinning the oil or thickening the displacing fluids. Many methods and materials have had- extensive laboratory and field testing, and many combinations have been proved to be effective for displacing oil. However, economic and technical constraints limit current choices to 10 methods which use a total of only 8 individual compounds or general groups of chemical substances which include: light hydrocarbons, nitrogen, carbon dioxide, surfactant formulations (including co-solvents and salts), water-solublenpolflers, alkaline materials, air, and water. Technical screening criteria forn selecting the methods appropriate for Permian Basin reservoirs are described. Economic limitations are also discussed. The technical and economic logic behind the big push for CO2 flooding in the Permian Basin are emphasized.