World's First Optical Venturi Flowmeter

Abstract

A new downhole optical Venturi flowmeter (OVFM) was developed that makes use of world's first optical differential pressure sensor (ODPS) and an optical pressure/temperature gauge. The use of Venturi flowmeters for downhole applications is not common because of the short life span of the associated electronics in the challenging downhole environment. The OVFM may therefore represent a more reliable solution for downhole applications when compared to its electronic versions.

The heart of the OVFM, the ODPS sensor, was developed between 2007 and 2014 as a part of a downhole multiphase flowmeter program that required differential pressure (ΔP) measurements. The ODPS measures the true ΔP with low uncertainty and is, therefore, superior to using two independent static pressure sensors with higher measurement uncertainties at the high pressures in a typical downhole environment. The performance of the OVFM was recently demonstrated in a multiphase flow loop test as a by-product of the aforementioned multiphase test program. The 100-bar test pressure represented a realistic downhole condition and the data from the single-phase test points and from one-phase dominant two-phase test points (i.e., liquid-rich/gas, gas-rich/liquid, and wet-gas flows) were analyzed to evaluate the performance of the OVFM with the ODPS sensor. In the process, modeling equations for Venturi discharge coefficient were also developed based on the multiphase flow data.

The results showed that the OVFM is in excellent agreement with the reference flow rates for single-phase, wet-gas, gas-rich/liquid, and liquid-rich/gas flows. By dynamically adjusting the density and viscosity of the fluid at the measured pressure and temperature (P and T) for the single-phase and one-phase dominant flows, and by using the ΔP measurements from the ODPS, the total-flow rates were successfully calculated. Because the ΔP measurement across the Venturi tube is fundamentally a static measurement, the OVFM is orientation-free and can be installed in any angle. Furthermore, this type of measurement is equally applicable to turbulent and laminar flows and, as a result, is a viable candidate for nonturbulent heavy oil applications. This paper provides a detailed discussion of performance results of the OVFM from the multiphase flow loop tests.

The OVFM represents a novel technology because the ODPS sensor is the first and only optical ΔP sensor for downhole applications. The optical nature of the sensor prevents any significant drift in the signal, and its true ΔP measurement capability provides increased accuracy in the flow measurement.