Method for reducing overflow of steam cavity and preventing top water from moving down in SAGD development process

The invention discloses a method for reducing overflow of a steam cavity and preventing top water from moving down in the SAGD development process. The method comprises the following steps of S100, determining the spatial development form of the current steam cavity; S200, determining main factors influencing the intrusion rate of the top water; S300, establishing a mathematical model of the rate of moving down of the top water by using the main factors determined in S200, and calculating the flow of water and oil under the current asphalt shell thickness; S400, evaluating the packing capacity of a top asphalt shell; S500, evaluating the influence of the pressure difference between the steam cavity and a top water layer on the intrusion rate of the top water; S600, establishing a technical boundary for preventing the top water from moving down. The pressure difference between the steam cavity and the top water layer needs to be controlled to reduce the risk that the top water moves downwards, and the SAGD pro