A Novel Low Tension Foam Flooding for Improving Post-Chemical-Flood in Shuanghe Oilfield

Abstract

Abstract Shuanghe oil field is a sandstone reservoir characterized by high water cut, poor sweep efficiency, and high heterogeneity with a long history of water flooding. The field has completed polymer flooding and is now under SP flooding. Although the SP flood is close to the end, the residual oil saturation is estimated to still be about 46~50% OOIP. Therefore, it is desired for future development of such reservoir to find an efficient method to recover residual oil. In this paper, we presented a new high-temperature resistant nitrogen foam system that gives a low oil/water interfacial tension and improves the sweep efficiency after SP flood. A novel high activity foam agent was prepared with unique surfactants and a high-temperature resistant foam stabilizer. This foam formulation is also able to lower the oil-water interfacial tension to the order of 10-2mN/m and create stable foam at high reservoir temperature. Firstly, the concentration of the foam agent was determined by interfacial tension and foam property. Then, the molecular weight and concentration of foam stabilizer was optimized by Ross-Miles method. Next, the properties of foam formulation were measured by Ross-Miles method at different temperatures, salinities, contents of Ca2+/Mg2+, aging time. The final optimal foam formulation is 0.35 wt% foam agent and 0.1 wt% foam stabilizer, which has a low IFT (5.31×10-2mN/m) and high foam stability index (>10000mLmin). Operating parameters such as foam injection modes, gas liquid ratio, injecting slug size were investigated at reservoirs conditions. The results reveal that, co-injection of gas and solution is a better option than alternating injection; the optimum gas-solution ratio is 1.5:1 by co-injection; the optimum foam injecting size is 0.5 pore volumes; and the injection rate was optimized as well. The foam flood performance was validated by comparing with other three EOR processes in a series of four oil displacement experiments. The four individual core floods are foam, polymer, gel and SP floods, and they were all injected after water flood. Among these four core floods, foam flood showed the best performance and highest oil recovery. An additional core flood was also done to mimic the field processes. The core was first water-flooded, polymer-flooded and SP-flooded, and then the foam was injected. The results showed the foam flood can effectively recover residual oil after the previous chemical processes. All the experimental results indicate this low-tension foam flooding could be a potential application in Shuanghe oil field.