The oil recovery enhancement by nitrogen foam in high-temperature and high-salinity environments

This article is designed for the application of Cocamidopropyl hydroxyl sulfobetaine (CHSB) in the nitrogen foam flooding under the high-temperature and high-salinity environments. Firstly, foam properties of CHSB were evaluated at different temperatures and varying salinity, as well as the effect of concentration on foam properties, and the long-term foam properties of CHSB were developed under different concentration. Then, a series of researches on controlling mobility of nitrogen foam were conducted in the sand-packs. Finally, nitrogen foam flooding was carried out in the sand-model and oilfield site. Results indicated that high-temperature was unfavorable to foam stability, and high-salinity could favor its stability. When CHSB was used as foaming agent at the concentration of 0.2 wt%, it showed excellent performance at the temperature of 120 °C and the salinity of 22×104 mg/L and good long-term stability after aging for 60 days. The foam flooding experiments showed that mobility reduction factor of foam increased with the residual oil saturation decreased or as the permeability declined in the high-temperature and high-salinity, and the residual resistance factor of foam during the subsequent waterflooding with 5 days shut-in was 3.8, which was obviously higher than that without shut-in or with shut-in in oil-free environment. The displaced area in sand-model was lager and wider in the presence of 5 days' shut-in than that in the absence of shut-in, and the water cut could be reduced to 38% and the enhanced oil recovery was about 17.8% after 5 days' shut-in. The oilfield test showed that the validity period of high oil production rate was more than half year and 2400 t of crude oil was produced in all.