Abstract: Based on the characteristics of the changes of the seepage flow parameter and fluid parameters，the change laws
of the gas well deliverability for different types of gas reservoir are proposed by using on-site testing data and experimental
analysis data of a gas well and the decline law is theoretically predicted，then the quantitative analysis and comparison with
the conventional methods are done by using the field data. In this paper，the analysis of the coefficients of the deliverability
equation changes are emphasized，and also the deliverability performance after the precipitous pressure decline is studied by
using the well test data. It is shown that the deliverability of the dry gas well is mainly controlled by the fluid parameters；
the rate of deliverability decline of the gas condensate well is affected by the composition change and the condensate dropout
when the reservoir pressure is below the dew point；the drawdown of the permeability and porosity during the development
will accelerate the deliverability decline in stress-sensitive gas field. By correcting the previous well testing data to predict the
decline performance for the above gas reservoir，it can satisfy the demand of productivity prediction and thus presents a basis
for the study of deliverability decline in gas reservoirs.

Key words: gas well, binomial coefficient, well testing, pseudopressure, deliverability equation