When wet gas is transported in a pipeline, liquid (condensate and water) will drop out due to temperature and pressure changes along the pipeline. The prediction of liquid holdup inside a pipeline is very important, as it will affect the prediction of pipeline pressure drop, downstream slug catcher design, scraping operation, etc. In performing pipeline steady-state liquid holdup and pipeline pressure drop calculations, one can choose either multiphase dynamic simulator or multiphase steady-state simulator. It was found that there could be significant differences in liquid holdup prediction when comparing the calculation results from different simulation methods. Using a typical hilly terrain, this paper presents the calculation results for wet gas pipeline liquid holdup and pressure. Different water and condensate loadings are considered. Gas flowrate is varied and different calculation methods are used.
Heavy component and water exists in the gas produced from gas production wells or gas-oil separation facilities. The pipeline can be in multiphase flow conditions when this wet gas is transported. It is very important to accurately calculate the pressure drop and liquid holdup in the multiphase flow pipeline for the design of the pipeline and other processing facilities. The accurate prediction of liquid holdup inside pipeline is also important for pipeline operation as the accumulated liquid inside the pipeline can potentially flood its downstream slug catcher due to slugging flow, gas flowrate rampup, or scrapping. Two different approaches have been practically used to Model pipeline multiphase flow. Ellul [1] has summarized these two approaches as Steady-State Approach and Transient Approach. Over the years, multiphase flow inside a pipe has been widely studied and correlations have been proposed to model the multiphase flow phenomena. These correlations include Beggs & Brill [2], Oliemans [3], Eaton [4], flanigan [5], etc. These correlations have been used for describing steady-state multiphase flow. Another method that used in steady-state calculations is the so-called Mechanistic Method [1]. The representatives for this method are OLGA Steady-State [6], Tacite Steady-State, and Xiao [7]. Empirical correlations and mechanistic methods are used in the softwares that are specifically designed for pipeline multiphase steady-state flow calculations.Dynamic simulations for pipeline multiphase flow have become more popular. The advance of computer power has made the dynamic simulation less time consuming. Dynamic simulation is based on solving the fundamental fluid flow equations in conservation of momentum, mass, and energy. Liquid holdup and pressure prediction can have significant differences among different calculation methods as well as in comparison with experimental data [6]. Shea [6] has compared several empirical correlations, mechanistic methods, and dynamic simulation results with experimental data. Ellul [1] summarized different approaches in multiphase flow modeling and compared the calculation results using an example. Steady-state and transient cases (ramp-up, scrapping) are studied. This paper studies multiphase pipeline pressure and liquid holdup predictions from different calculation methods that are available in commercial software using a typical hilly terrain. Different flowrates and liquid loading (for both condensate and water) are used.
