Density Measurement of Three-Phase Flows Inside of Vertical Piping Using Planar Laser Induced Fluorescence PLIF

Abstract

Planar laser induced fluorescence (PLIF) is a measurement technique that can be used to provide a laboratory reference for validating the performance of field instrumentation that either directly measures mixture density or infers it from a combination of ancillary techniques. PLIF density measurements offer high-speed response and the ability to resolve minute flow features in transient flow patterns. Fundamentally, PLIF can also be used to verify multiphase flow models and predictive tools that are used for designing production piping. The use of PLIF to determine an instantaneous mixture density of two-phase flows has been successfully accomplished in previous fundamental laboratory studies found in literature. However, the use of this technique to determine the mixture density of three-phase flows for field-related scenarios has not been previously evaluated. To assess PLIF as a potential reference measurement system, a testing effort was undertaken to measure the instantaneous mixture density from a comingled oil-gas, water-oil, and oil-water-gas flow that was subjected to slug, churn, and bubble transient flow conditions inside of vertical piping. The objective of this work was to compare and validate the results obtained using the PLIF measurement approach against a commercially available gamma densitometer and tomography system for a variety of flowing conditions. The PLIF technique was able to resolve transient flow features and density values for both two-phase and three-phase flows through the piping. Distinct slug flow features such as the slug head, gas pocket, pocket collapse, and the tail were captured by PLIF and were observable in the raw image sequence captured by a high-speed camera. Additionally, the results for a variety of water-oil-gas flowing conditions were within 3% difference of a mixture density model that was calculated from liquid and gas flow measurements utilized in the test facility. The comparison of the PLIF results to the reference instrumentation indicates that this technique is successful at obtaining a mixture density for steady and transient oil, water, and gas comingled flows.