Prediction of Transient Behaviors of Gas-Condensate Two-Phase Flow in Pipelines With Low Liquid Loading

Abstract

Transporting natural gas and gas condensate in a long distance pipeline occurs frequently during the development of offshore or desert gas condensate and/or oil fields. However, the thermohydraulic calculation of gas-condensate pipeline, especially transient flow simulation, is hitherto a challenging issue in the pipeline industry on account of a maze of complexities of pipeline undulation, changeable properties of fluid, and transfer of momentum, mass and heat. This study is intended to predict the transient flow behavior in gas-condensate pipelines. In the paper, a hydraulic and thermodynamic (such as phase behavior and properties) model for the analysis of transient gas-condensate two-phase flow in pipelines with low liquid loading is outlined. The hydraulic model is based on simplified “No Pressure Wave” model where the constitutive relation results from the Ottens et al (2001) correlation. An implicit method, the convergence and stability of which have been verified by example calculations, is utilized to solve the transient flow model equations of gas-condensate pipelines. In the end, the transient performances of low-liquid-loading gas-condensate two-phase non-isothermal flow in undulating pipelines, which are subjected to boundary conditions of increasing or decreasing inlet flow rate and specified outlet pressure with time, are numerically investigated. The results, such as pressure and liquid holdup profiles vs. time, and time evolutions of outlet condensate flow rate and accumulated liquid content etc., show that the presented model and numerical method for analyzing gas-condensate transient flow behaviors in pipelines looks reasonable.