Foam flooding is one of promising enhanced oil recovery (EOR) methods for waterflooded reservoirs due to its good mobility control capability. However, its application in high-temperature and high-salinity reservoir has always been a challenge. This work presents salt-tolerant foam that can be used at about 100 °C under the salinity of more than 200000 mg/L (Ca2+ + Mg2+ >10000 mg/L). Its displacement efficiency was evaluated at different permeability heterogeneity conditions.

The surfactant (foaming agent) solution was prepared using reservoir formation water (total salinity 204672 mg/L, Ca2+ + Mg2+ 11480 mg/L) obtained from a reservoir in Tarim Basin, China. The displacement efficiency of foam was investigated in different permeability conditions (35.47, 72.72, 165.75, 265.28, 410.73, 600.38, and 950.11 mD) using single-core flooding experiment and in different permeability heterogeneity (permeability max-min ratio of 3.34, 6.62, 9.22, and 11.98) using parallel-core flooding experiments (one high-permeability core and one low-permeability core). For all flooding experiments, nitrogen foam was used by co-injection of nitrogen and surfactant solution.

For all permeability conditions in single-core flooding experiments, after water flooding with a 98% water cut, the injection of foam could increase the injection pressure. Foam injection together with its subsequent water flooding could yeild an additional oil recovery of 11.73, 12.35, 12.8, 13.04, 15.45, 16.04, and 17.51% under the permeability of 35.47, 72.72, 165.75, 265.28, 410.73, 600.38, and 950.11 mD, respectively. Obviously, the yielded additional oil recovery increased with permeability. Under the permeability max-min ratio of 3.34, 6.62, and 9.22, an addtition oil recovery can be yielded from both high- and low-permeability cores, but the additional oil recovery from low-permeability core was higher. This implies that the injection of foam can not only improve displacement efficiency after water flooding, but also can effectively increase flow resistance in high-permeability core, and thus improving oil recovery in low-permeability core. However, when the permeability max-min ratio was increased to 11.98, the oil in low-permeability core cannot be mobilized even after foam injection, which means that foam injection can effectively work only in a certain permeability heterogeneity condition. When permeability heterogeneity is strong, enhanced foam should be considered to increase the strength of foam using polymer (only for low temperature), gel or nanoparticles, etc.

The obtained results show that the developed foam formulation has a great potential for improving displacement efficiency and sweep efficiency in water-flooded heterogenous reservoirs with very high temperature and ultra-high salinity.

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