Quick estimation of gas pipeline inventory

Quick estimation of the pipeline inventory at the end of fiscal periods is common practice in companies dealing with the transmission of natural gas. The accuracy of line pack estimation depends on the accuracy of estimating the mean value of the gas density (or specific volume) which depends on composition and the distribution of pressure, temperature, and compressibility factor along the pipeline. An improved line pack estimation formula is developed for natural gas flowing in a horizontal pipeline. The derived formula takes into consideration the variation of velocity, pressure, temperature, and compressibility factor along the pipeline. Numerical results comparing the errors associated with line pack estimation on the basis of alternative approximations to the mean pressure, temperature, and compressibility factor are presented. The errors entailed on using different approximations depend on the gas composition, and the magnitude of the pressure and temperature ranges existing at the extremities of the pipe segment.