Deep well oil casing annulus entrapment pressure prediction method

The invention discloses a deep well oil casing annulus entrapment pressure prediction method which comprises the following steps: averagely dividing a shaft into n sections, and sequentially calculating the temperature and pressure of each section; solving the liquid holdup and fluid physical property parameters of the well section based on the drift model; the temperature drop gradient and the pressure drop gradient of the well section are calculated based on a temperature-pressure model formula, and then the temperature and the pressure of an outlet are obtained; the obtained temperature and pressure result is compared with the temperature and pressure of the outlet of the assumed well section, and the temperature and pressure of the inlet of the next section are determined according to the difference value till the temperature and pressure of the whole shaft are calculated; dividing a shaft annulus trap into an annulus gas section and an annulus liquid section, and respectively calculating a pressure incre