Further Investigation of High-Temperature Alkaline Floods

Abstract

Effectiveness of alkalies, such as NaOH, Na2Si03, and Na2C03, to recover residual oil during hot waterfloods (356°F [l80°C]) was investigated and compared. These alkalies, with or without surfactants, may be added to steam to enhance oil recovery from that portion of the reservoir subjected to a hot waterflood during steam injection. Tertiary flood rate and concentration of the injected alkalies were changed and their corresponding effects on recovery efficiency, WOR, recovery mechanism. and alkali consumption were studied. Some lower-temperature floods were also performed with caustic. Dynamic interfacial tensions (IFT's) between the acidic crude oil and the alkaline solutions at different pH's were measured at elevated temperatures up to 356°F [l80°C] with a drop-weight technique. For some alkalies (e.g., NaOH), the effects of salt and surfactant addition were also investigated.The results show that dynamic IFT's between the acidic crude oil and the alkaline solutions increase with increase in temperature. At high temperatures, IFT values at low pH approach values obtained for distilled water. This is more pronounced for caustic than for sodium metasilicate and sodium carbonate. The same IFT values obtained for caustic at elevated temperatures can be obtained with sodium carbonate and sodium metasilicate at a lower solution pH. Although IFT and alkali consumption increase with an increase in temperature, recovery efficiencies obtained at high temperatures were comparable with those obtained at lower temperatures. This could result from ease in flow of emulsions at high temperature. Recovery efficiencies obtained with sodium metasilicate at 356°F [l80°C] were higher than those for sodium carbonate and sodium hydroxide. These recoveries took place at IFT values as high as I dyne/cm [I mN/m]. Oil was always recovered with the injected chemicals, and no significant oil bank was formed.

Interactions between Acidic Crude Oil and Alkali and Their Effects on Enhanced Oil Recovery

“…They observed an important initial combination of rapid reversible adsorption and chemical reactions followed by slower non-reversible chemical reactions that can later assume great importance because of the long contact time that may prevail in flooding a petroleum reservoir. Mehdizadeh and Handy studied the effectiveness of alkaline, such as NaOH, sodium orthosilicate, and Na 2 CO 3 , to recover residual oil during hot water floods. They claimed that, although IFT and alkali consumption increase with an increase in the temperature, recovery efficiencies obtained at high temperatures were comparable to those obtained at lower temperatures.…”