The development of extra-low permeability reservoirs (air permeability<10md) is a crucial challenge due to the high injection pressure and low oil production. Many methods had been used for low permeability reservoirs to improve the performance, such as hydrofracturing, surfactant flooding, cycle injection, etc. It was found that the small pores dominate the fluid flow and displacement in low permeability porous media, so the capillary forces plays primary role in water oil displacement. For water-wet systems capillary forces assist brine imbibing into pores, whereas for oil wet case they tend to act as resistance. It is believed the wettability alteration from oil wet to water wet or to intermediate plays a beneficial role to lower the injection pressure and enhance oil recovery, but the flow mechanisms and the significance of wettability alteration for extra-low permeability reservoirs is ambiguous. A series experiments were conducted for investigating the effect of wettability alteration on relative permeability for oil-wet reservoir sandstones rock with air permeability range from 0.1 millidarcy to 2.0 millidarcy. The results indicate that both water and oil relative permeability curves are dependent strongly on wettability alteration. In particular, the co-flowing zones were extended remarkably and the recovery efficiency was improved by injection of thin film spreading agent solution.

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