CFD-Based Sensitivity Study of Flow and Design Parameters in Multiphase Flow Meters. Analyzing the Impact of Variable Conditions on Homogeneity and Measurement Accuracy

Abstract

In subsea oil- and gas applications, multiphase flow meters (MPFM) are used to measure volumetric flow rates of oil, gas and water produced from a well, without first separating the phases. When well productions decline the flow may become unstable, requiring additional controls. In these cases MPFMs are useful instruments to detect well instability, blockages and disturbances so that the well can be controlled and stabilized in real time. Variations in flow regime and homogeneity in the Venturi-based MPFM may affect the accuracy of measured volume flow. Additionally, understanding slip velocity between phases is crucial for formulating an accurate slip model to compute phase volume flow rates.

In this project, the sensitivity of the MPFM to flow- and geometrical parameters is studied by modeling and simulating the MPFM using CFD. This gives insight into how MPFM design and operating conditions influence measurement certainty on a macroscopic scale, while also allowing for the investigation of smaller scale phenomena. Time-averaged mean values and periodic behaviors of the flow parameters are evaluated to give insight into the flow behavior and the MPFM sensitivity to flow and design parameters. The homogeneity and mixing of the flow before entering the MPFMs is evaluated, to understand how operating conditions and geometry changes affect the flow characteristics considering MPFM accuracy. Additionally, a suitable CFD modeling technique is found to aid in the design and development of future MPFMs. The modeling technique is evaluated in terms of accuracy, quality and computational expense.

In this study, a suitable modeling method was identified using Eulerian Multiphase models. These models have high accuracy and is effectively capturing the flow behavior while being computationally efficient. The slip-ratios evaluated showed that for increased pressure and viscosity the liquid film, dispersed, and overall slip decreased while for design changes the slip had more mixed results. The sensitivity study revealed that the MPFM’s sensitivity to geometrical parameters, such as blind-T depth and vertical entrance length, was minimal. Operating conditions, especially pressure and liquid viscosity, play a major role in shaping the flow regime and phase mixing. These factors can significantly affect MPFM accuracy if they are not properly accounted for in the interpretation models.