Based on the volume source

we established an unstable state model of coupling the horizontal wells to the gas reservoir

considering the friction resistance of the wellbore

the acceleration pressure loss and the influence of the wellbore inflow. It is showed that the calculation results of this model fit well with the commercial numerical simulation software--Eclipse

and has proven the correctness of this simulation method. The results show that we may overestimate the production of the horizontal wells when the wellbore pressure drop is neglected. The flow distribution of the horizontal wells is affected by the factors such as the wellbore inflow

acceleration and friction. And the influence of the gas production profile in the period of the unstable state is greater than that of the quasi-steady state.