Method for determining dynamic change of pressure gradient to be started after heavy oil water drive is converted into hot water drive

The invention discloses a method for determining dynamic change of a pressure gradient to be started after heavy oil water drive is converted into hot water drive. The method comprises the following steps: 1, collecting geological reservoir static data of a target block; 2, determining a relational expression of oil sample viscosity and temperature of a target block; 3, testing the quasi-starting pressure gradients of the core and the oil sample of the target block under different temperature and permeability conditions; 4, obtaining a change relational expression of the starting pressure gradients at different temperatures along with the fluidity; 5, obtaining formation temperature field distribution of different stages of the hot water flooding process of the target block; 6, calculating a starting pressure gradient according to the geological reservoir parameters of each grid; and 7, drawing starting pressure gradient distribution diagrams of different stages of hot water drive of the target block. Accordi