A computational fluid dynamics approach to improve multiphase flow measurement in a vertically installed venturi-based multiphase flowmeter

• Main Author: Zhan, Mengke
• Other Authors: Shu Jian Jun
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/170038
• Institution: Nanyang Technological University

Multiphase flowmeters (MPFMs) have been widely used in the production monitoring of upstream oil and gas wells with co-produced water. An MPFM generally consists of phase fraction and velocity (hence flow rate) measurements. Real-time in-line interpretation of liquid properties is also important for multiphase flow measurements; for example, many phase fraction measurement principles have a dependency on characteristics of water salinity. Despite the advantages of being able to perform continuous, inline, real-time oil-gas-water flow rate measurement without fluids separation, several challenges have been identified to further improve MPFM performance. Some of the challenges include difficulties to (i) improve the design parameters of upstream piping of vertically-installed MPFMs to establish flow homogeneity in order to maintain measurement accuracy and minimize manufacturing cost and carbon footprint, (ii) to identify a near-wall liquid-rich and water-liquid-ratio (WLR) representative location suitable for salinity and WLR measurement, and (iii) to scale multiphase flows with different fluid properties and flow conditions for generalities of the flow model. This study uses a computational fluids dynamics (CFD) approach, particularly the Eulerian-Eulerian multiphase framework with various models on interphase forces, to address the challenges in a vertically installed Venturi-based MPFM downstream a horizontal blind-tee. The simulation results are verified against experimental data collected at SLB and National University of Singapore (NUS) multiphase flow facilities. To recommend the suitable design parameters for the MPFM upstream piping, the main effects of the variations in the vertical entrance length (VEL from 3D to 16D) and in the horizontal blind-tee depth (HBD from 1.5D to 3D) on the Venturi phase fraction, differential pressure, two-phase discharge coefficient, and local liquid properties are quantified. Considering the trade-off between achieving good MPFM flow model accuracy (that requires a large VEL for flow homogeneity) and reducing manufacturing cost and carbon footprint (that requires a small VEL), the study identifies that the suitable design parameters are 6D for VEL and 1.5D~2D for HBD. A correlation to determine gas volume fraction (GVF) from the gas phase fraction measured by a gamma-ray sensor at Venturi throat has been established for a given VEL (≥ 6D), in order to reduce the dependency of phase fraction (and GVF) measurement on the variation in VEL. To identify a near-wall location suitable for water salinity and WLR measurement, the liquid-richness and WLR representativeness are evaluated at four different sensing locations along the vertical Venturi. The CFD simulation results, validated by experiments, show that the Venturi inlet is the most suitable location for liquid-property measurement by a microwave sensor, compared to the mid-convergence section, mid-divergence section and the Venturi outlet. The microwave sensor installation integrated with a vertically installed Venturi can further reduce MPFM carbon footprint without requiring the sensor at the horizontal blind-tee location. Scaling studies have been performed in this research on the gas-liquid two-phase flows in a vertical Venturi where flows are developing. Different from the previous work which focused on separated flows, the effect of phase interactions is studied. Phase fraction in the Venturi is found to be dependent on the dimensionless numbers related to the phase interaction terms. Useful scaling rules to obtain phase fraction have been developed, with good agreement with the measurement. The analytical equation to obtain the Venturi dimensionless differential pressure from a set of dimensionless numbers, and the relationship between two-phase discharge coefficient and liquid Reynolds number can also be used to predict the Venturi differential pressure and the frictional loss that needs to be accounted for to obtain accurate mass flow rate. The developed correlations can be used to potentially reduce the cost (and carbon footprint) required to perform flow experiments and CFD simulations, as phase fraction, Venturi differential pressure, and two-phase discharge coefficient can be readily predicted, given the dimensionless numbers of the gas-liquid flow.