Comparison of Sodium Carbonate, Sodium Hydroxide, and Sodium Orthosilicate for EOR

Abstract

Summary Alkaline and alkali/polymer flooding are economical and versatile techniques proposed for application in EOR. Recently, the use of high-pH alkaline chemicals was emphasized to obtain low interfacial tensions (IFT's) with the crude oil and to counteract alkali loss by both reservoir rock and interstitial water reactions. This experimental study compares the utility of sodium carbonate (Na2CO3) buffer solutions with sodium hydroxide (NaOH) and sodium orthosilicate (Na4SiO4) at equal Na2O levels for alkaline and alkali/polymer flooding. The alkalis were found to be equally effective in reducing IFT with Wilmington Ranger zone crude, and eight other acid crude oils. Tertiary recovery results from 20 Berea corefloods with the Ranger zone crude and hard reservoir brine were equivalent (6 to 17%) for Na2CO3, NaOH, and Na4SiO4. Similar modest recoveries were obtained for polymer floods that used Polyacrylamide or xanthan gum. However, polymer augmentation of alkaline floods dramatically increased tertiary oil yields to 73 to 95%. In addition, alkali improved the injectivity of polymer solutions. The alkali reactions with sandstone were much less severe with Na2CO3 than with NaOH or Na4SiO4.