The invention discloses a determination method for alternate injection opportunity of gel /
polymer flooding. According to the determination method, alternate opportunity 1, alternate opportunity 2 and alternate opportunity 3 are determined according to the output liquid
moisture content and injection quantity of
oil displacement systems. The alternate opportunity 1 is the opportunity corresponding to the time when the output liquid
moisture content reaches a certain value. The alternate opportunity 2 is the opportunity corresponding to the time when the injection quantity of the
oil displacement system 2 is 0.05-0.3 PV. The alternate opportunity 3 is the opportunity corresponding to the time when the injection quantity of the
oil displacement system 3 is equal to the difference value of 0.45 PV and the injection quantity of the oil displacement
system 2. The
viscosity, obtained through change injection in the alternate opportunity 1, of the oil displacement system 2 is larger than the
viscosity, obtained through prior injection, of the oil displacement system 1. The
viscosity, obtained through change injection in the alternate opportunity 2, of the oil displacement system 3 is smaller than the viscosity of the oil displacement system 2. Through the determination method, heterogeneous oil reservoirs conducting chemical flooding can obtain different oil displacement effects, and thus the usage degree of a low permeable layer is improved.