Research and Application of Transient Wellbore Flow Model in Intermittent Production Gas Wells

In intermittent - producing gas wells, there exists an interaction between the wellbore and the formation during the opening and closing periods. Nevertheless, the current multiphase flow models for wellbore - formation coupling are not yet perfect. In this paper, a mathematical model of unsteady wellbore flow is established based on the principles of mass conservation and momentum conservation. This model is capable of simultaneously describing the flow, holdup, and gas - liquid transfer in both the tubing and the casing annulus. The numerical method is employed to solve the partial differential equation. Specifically, the finite - difference method is utilized to discretize the mathematical model on the grid system, thereby forming the corresponding fully implicit difference equations, which are ensured to meet the requirements of compatibility, convergence, and stability. To verify the accuracy of the model, a simulation calculation is carried out on Well Su 38 - X using the new model. The simulation results demonstrate that the calculation results of the new model can accurately reflect the variations in bottom - hole pressure and wellhead pressure during the well opening and closing periods. It is revealed that the removal of fluid decreases the water saturation in the formation near the well bottom, which is beneficial for enhancing the gas - phase permeability and thus increasing the gas - well production.