Method for predicting SAGD oil production speed of heavy oil reservoir

The invention discloses a method for predicting the SAGD oil production speed of a heavy oil reservoir. The method comprises the steps that the oil reservoir is divided into a plurality of small layers according to the oil reservoir size, the maximum steam cavity included angle of a fan-shaped oil drainage area of a steam cavity, small interlayer steam cavity included angle change, small interlayer included angle change of a side face oil drainage area of the steam cavity, the oil reservoir thickness and the steam cavity front edge distance change value; when the steam cavity does not grow to the production well, the maximum diffusion velocity of the steam cavity in the initial stage of the SAGD after preheating is completed is calculated; determining t-moment oil production speed of the ascending stage, the transverse development stage and the descending stage of the steam cavity; respectively changing the thickness of the oil reservoir, the oil phase permeability and the viscosity of the crude oil, and repe