Use data of bottom pressure restoration of well with right angle coordinate system to draw P-T curve

and then chose two time-points(t

1

t

23

) from the average value

read out corresponding P

1

P

2

and P

3

value

produce time curve slope and productivity index on the basis of the plate.Interval between each point shall be chosen as following rule;interval between t

1

and t

2

shall not be too small

40mm for t

1

and 300mm for t

2

.The establishment of this method is mainly on the basis of theory of slug flow test.Predicative results got from an oil field in eastern China by this method are almost as same as practical testing results.