Comparison of Sodium Carbonate, Sodium Hydroxide, and Sodium Orthosilicate for EOR
- J.H. Burk (Stauffer Chemical Co.-CPI)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- February 1987
- Document Type
- Journal Paper
- 9 - 16
- 1987. Society of Petroleum Engineers
- 5.4.10 Microbial Methods, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.4.1 Waterflooding, 5.3.2 Multiphase Flow, 5.4 Enhanced Recovery, 5.2.1 Phase Behavior and PVT Measurements, 4.2.3 Materials and Corrosion, 1.6.9 Coring, Fishing, 5.3.4 Reduction of Residual Oil Saturation, 5.2 Reservoir Fluid Dynamics
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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.
Over the last 10 years, numerous reports have been published on the theory of alkali interaction with reservoir published on the theory of alkali interaction with reservoir rock and fluids and on experimental work with alkaline flooding. The majority of the alkaline floods in the field and most laboratory studies have been carried out with NaOH or Na4SiO4. Use of high pH and high alkali concentrations of up to 5 wt% was deemed necessary to obtain low IFT's with the acid crude oils, to counteract alkali loss, and to decrease alkali retention time in the formation.
Na2CO3 and other alkaline buffers that have a lower pH than NaOH or Na4SiO4, have not been studied extensively. pH than NaOH or Na4SiO4, have not been studied extensively. The use of an alkali buffer (such as Na2CO3) could be advantageous, because the buffered slug would be less reactive with sandstone minerals because of reduced hydroxyl ion activity. The slug's lower pH would be maintained over a wide concentration range despite alkali consumption within the formation. Results from very early field flooding trials with Na2CO3 were not conclusive. More recent field tests with Na2CO3 look promising, however, especially the successful implementation of a Na2CO3/polyacrylamide polymer flood in the Isenhour, WY, field. Use of alkali in conjunction with polymer to obtain low tension and improved mobility ratio has polymer to obtain low tension and improved mobility ratio has been shown to increase tertiary oil yields substantially; more specifically, a Na2CO3/polyacrylamide system was reported to be very effective in laboratory corefloods.
On a contained-Na2O basis, Na2CO3 is cost-effective compared with NaOH or Na4SiO4 because, unlike the other alkalis, it is readily available from vast trona deposits in Wyoming. NaOH and Na4SiO4 prices can fluctuate substantially with economic conditions because their manufacture is tied to other processes. This experimental study presents a side-by-side comparison of NaOH and Na4SiO4 with Na2CO3 on an equal contained-Na2O basis. The equal Na2O convention was chosen in preference to a comparison on an equal weight-percent basis after preliminary screening showed similar low-tension IFT behavior and oil recoveries at equal Na2O levels. Results from IFT measurements and alkaline and alkali/polymer corefloods are reported. The aspects of divalent ion precipitation, slug injectivity, and alkali retention and consumption are discussed.
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