The surface crude oil viscosity of the first ultra-heavy oil field in Bohai Oilfield is more than 50,00mpa·s, which is unable to be developed under the condition of original formation temperature and requires steam stimulation. In the first period of steam huff and puff well, due to sufficient formation energy, steam injection pressure is high in the process of steam injection. The measures to reduce the steam injection speed are mostly adopted in the field, but it will lead to the problem of large wellbore heat loss and affect the steam stimulation heat injection effect. In this paper, based on the oil characteristics of the first ultra-heavy oil field in Bohai Oilfield, the evaluation of oil soluble surfactant was carried out, and the experimental study of pre-injection of oil soluble surfactant to reduce steam injection pressure was carried out. It has been successfully applied in the development of the first ultra-heavy oil in Bohai oilfield. The results show that the oil soluble surfactant with asphaltene dispersibility has better temperature resistance and viscosity reduction effect, and the viscosity reduction effect is more than 95% before and after aging. Laboratory experiments show that the oil soluble surfactant can reduce the steam displacement resistance of the displacement front and the affected area. When the injection amount of oil soluble surfactant is 0.2PV, the maximum steam injection pressure can be reduced by 22.9% and the steady steam injection pressure by 10.8%. The design treatment radius of oil soluble surfactant is 0.15m, and the field test shows that the steam injection pressure decreases by 1.1MPa during steam injection.

After adopting the depressurization and increase injection volume technology, the field injection pressure is effectively reduced, the steam injection effect of ultra-heavy oil is guaranteed, and the technical guarantee for the subsequent development, promotion and application of ultra-heavy oil is provided.

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