Abstract: To study production decline model dominated by late-boundary flow for constant volume tight gas reservoir, and to provide a theoretical basis for gas reservoir performance analysis and index prediction. Based on experimental results of seepage mechanism for tight gas reservoir, after analyzing and establishing the seepage differential equation of tight gas reservoir, focusing on the late stage of boundary flow of constant volume tight gas reservoir, combined with material balance equation, a new equation and its differential equation were both proposed for the gas production vs time, and based on which, the quantitative model of initial decline rate and geological factors was determined. The results show that:(1) compared with conventional gas reservoirs, the non-Darcy flow pressure loss in tight gas reservoirs consists of three parts, which are derived from fluid internal friction, turbulence effect and start-up pressure, which is also an important reason for the anomaly of binomial productivity equation. (2) Because of turbulence effect and start-up pressure, Arps$'$s decline model was not followed for gas wells of constant volume tight gas reservoir, and the existence of start-up pressure gradient and the turbulence effect slows down the production decline rate of gas wells, and the gas well production decline model follows exponential decline, only when the turbulence coefficient tends to 0, without start-up pressure gradient, and the pseudo time is used instead of time. (3) The example shows that the binomial productivity anomaly can be effectively eliminated by introducing the start-up pressure term, and the reservoir parameters such as gas well dynamic reserves and start-up pressure gradient can be calculated by using the new model, which lays a theoretical foundation for the analysis of main controlling factors of production decline, formation parameter inversion and dynamic index calculation of constant volume tight gas reservoir, abnormal treatment of binomial equation in tight gas reservoir included, so it has strong practicability and foresight.

Key words: production decline, tight gas reservoir, seepage mechanism, start-up pressure, turbulence coefficient