Abstract
Due to the complex nonlinearity characteristics, analytical modeling of compressible flow in inclined transmission lines remains a challenge. This paper proposes an analytical model for one-dimensional flow of a two-phase gas-liquid fluid in inclined transmission lines. The proposed model is comprised of a steady-state two-phase flow mechanistic model in-series with a dynamic single-phase flow model. The two-phase mechanistic model captures the steady-state pressure drop and liquid holdup properties of the gas-liquid fluid. The developed dynamic single-phase flow model is an analytical model comprised of rational polynomial transfer functions that are explicitly functions of fluid properties, line geometry, and inclination angle. The accuracy of the fluid resonant frequencies predicted by the transient flow model is precise and not a function of transmission line spatial discretization. Therefore, model complexity is solely a function of the number of desired modes. The dynamic single-phase model is applicable for under-damped and over-damped systems, laminar, and turbulent flow conditions. The accuracy of the overall two-phase flow model is investigated using the commercial multiphase flow dynamic code OLGA. The mean absolute error between the two models in step response overshoot and settling time is less than 8% and 2 s, respectively.
Highlights
The oil and gas industry has been looking for a long time into the development of reliable technologies and practices to be able to properly assess and understand the dynamics of multiphase flows within transmission lines
Having a simplified, analytical yet accurate model is crucial so that transmission line flow models can be integrated with other oil and gas equipment models to analyze the behavior of the whole complex system, achieve tasks that require real-time calculations as well as having a fast and reliable tool that can be deployed during the design and optimization phase of oil and gas development projects
Approximated transfer functions proposed in Equations (43)–(46) are obtained for under-damped transmission lines
Summary
The oil and gas industry has been looking for a long time into the development of reliable technologies and practices to be able to properly assess and understand the dynamics of multiphase flows within transmission lines. In addition to steady-state flow conditions, numerous studies have been conducted to model transient two-phase flow systems based on either a two-fluid model [12] or a drift-flux model [13] In both cases, the models are developed mainly on the basis of introducing a full set of conservation equations (mass, momentum, and energy). A comprehensive mechanistic model is adopted to estimate steady-state liquid holdup and pressure gradient, which will be used to derive equivalent single-phase fluid parameters, namely, altering the fluid parameters of density, Fluids 2021, 6, 300 viscosity, and bulk modulus as a function of gas volume fraction (GVF) These steady-state parameters are integrated within the analytical dynamic single-phase model to predict transient flow behavior in inclined transmission lines.
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