Enhancements in Fraction Measurements and Flow Modeling for Multiphase Flowmeters

Abstract

Multiphase flowmeters (MPFMs) have been used since the early 1990's in the oil and gas industry and have gained acceptance in many environments. They have been considered the primary metering option for a wide range of applications - from heavy oil to wet gas. The combination of operational benefits, measurement robustness, demonstrable accuracy, and auditability has improved their status from new, unproven technology to that of the premium mainstream metering option. With more than a decade of experience acquired using a combination venturi and gamma-ray multiphase flowmeters, further gains in measurement quality and operational robustness have been achieved. We will illustrate how enhancements in fraction measurements using multi-energy gamma ray attenuation and a more comprehensive analysis of the gamma-ray spectrum have been developed and implemented to provide better measurement accuracy and stability, leading to enhanced performances in multiphase flow measurements. Another area of improvement that has been pursued is in the field of modeling of multiphase flows through a venturi. Historically, single-phase flow equations have been used, being adapted to multiphase flows by semi-empirical means to account for their complexity. While such models have proven robust for most standard applications, they can reach some limitations in particular conditions. We will present how a more dynamic model that considers the nature of the flow has led to improved accuracy of multiphase flow measurements. We present the scientific basis for the new enhancements as well as illustrate the accuracy gains achieved based on hundreds of flow loop test points, ultimately leading to the quantification of the accuracy gains obtained through those technological improvements.

Microwave probe sensing location for Venturi-based real-time multiphase flowmeter

“…Some assumptions are made to simplify the Eulerian-Eulerian governing equations. First, a steady framework is used instead of a transient one, because (i) the flow loop experiment used for validation has steady inlet condition; (ii) the flow rate output is computed at a frequency of 1 Hz for gamma-ray full-spectrum deconvolution (Chazel et al, 2014), which can be considered as the "average flow rate" over a second duration; (iii) in steady flow, steady-state simulation produces the equivalent of time-averaged transient results. To show that the flow reaches a steady-state, the time-series data of the water-nitrogen flow rates for the Venturi throat chord-average liquid fraction l From Fig.…”

“…In the phase fraction measurement technique, single-energy gammaray attenuation is commonly used to measure the chord-averaged phase fraction of gases and liquids with sufficiently different densities (Saetre et al, 2010). Through dual-energy gamma-ray attenuation, the phase fraction of gas, oil, and water can be measured to calculate the water-toliquid ratio (WLR) (Chazel et al, 2014). For an MPFM based on single-energy gamma-ray attenuation, only the fraction of gas or liquid can be measured; an additional measurement of the flowing mixture conductivity and/or permittivity can be used to determine the water fraction (and hence the WLR).…”