Pseudo slug flow in viscous oil systems – experiments and modelling with LedaFlow

An experimental two-phase flow campaign with a viscous oil (100 cP) was conducted in the Large Scale 8" loop at the SINTEF Multiphase Flow Laboratory. The loop consisted of three main test sections, with pipe inclinations 0, 0.5 and 90 degrees, and with approximate lengths of 380 m, 380 m and 50 m, respectively. The experiments were performed at system pressures 20, 45 and 85 bara. The primary focus of the campaign was on liquid dominated flows in horizontal/near-horizontal pipes, with particular emphasis on the laminar-to-turbulent transition in the liquid. The main instruments were DP-cells for pressure drop measurements, and narrow beam gamma densitometers to measure the liquid height. In addition, traversing gamma densitometers were mounted on each of the two near-horizontal sections to measure the time-averaged liquid distribution and volume fractions. In this campaign, it was found that at high pressure, the slug flow region was very narrow. In particular, at low gas-liquid ratios, the prevailing flow regime was determined to be a kind of "pseudo slug flow", which was characterized by large waves that did not quite extend to the top of the line. Simulations with the commercial multiphase simulator LedaFlow [1] did not reproduce this at the time, and the penalty for this discrepancy was that the predicted pressure drop was too high. Consequently, it was concluded that the physical models in LedaFlow needed improvement to predict these conditions better. Through detailed analysis of the experimental data, it was found that at these conditions, slugs were often not able to form because the waves did not have sufficient inertia to sustain a slug front. This limitation was not accounted for in the flow regime criteria in LedaFlow, so to improve the situation, the existing slug flow model in LedaFlow was generalized to cover pseudo slug flow in addition to regular slug flow. By introducing this new pseudo slug flow regime, the pressure drop predictions in viscous oil systems became significantly more accurate than before.publishedVersio

Pseudo slug flow in viscous oil systems – experiments and modelling with LedaFlow

An experimental two-phase flow campaign with a viscous oil (100 cP) was conducted in the Large Scale 8" loop at the SINTEF Multiphase Flow Laboratory. The loop consisted of three main test sections, with pipe inclinations 0, 0.5 and 90 degrees, and with approximate lengths of 380 m, 380 m and 50 m, respectively. The experiments were performed at system pressures 20, 45 and 85 bara. The primary focus of the campaign was on liquid dominated flows in horizontal/near-horizontal pipes, with particular emphasis on the laminar-to-turbulent transition in the liquid. The main instruments were DP-cells for pressure drop measurements, and narrow beam gamma densitometers to measure the liquid height. In addition, traversing gamma densitometers were mounted on each of the two near-horizontal sections to measure the time-averaged liquid distribution and volume fractions. In this campaign, it was found that at high pressure, the slug flow region was very narrow. In particular, at low gas-liquid ratios, the prevailing flow regime was determined to be a kind of "pseudo slug flow", which was characterized by large waves that did not quite extend to the top of the line. Simulations with the commercial multiphase simulator LedaFlow [1] did not reproduce this at the time, and the penalty for this discrepancy was that the predicted pressure drop was too high. Consequently, it was concluded that the physical models in LedaFlow needed improvement to predict these conditions better. Through detailed analysis of the experimental data, it was found that at these conditions, slugs were often not able to form because the waves did not have sufficient inertia to sustain a slug front. This limitation was not accounted for in the flow regime criteria in LedaFlow, so to improve the situation, the existing slug flow model in LedaFlow was generalized to cover pseudo slug flow in addition to regular slug flow. By introducing this new pseudo slug flow regime, the pressure drop predictions in viscous oil systems became significantly more accurate than before

Simulation of two-phase viscous oil flow

Multiphase flows of heavy oils and other fluids with high apparent viscosity is a particular industrial challenge. Main challenges here is that interfacial waves, atomization at the large scale gas–liquid interface as well as bubble entrainment and separation all are significantly modified by high fluid viscosity. In addition the viscous liquid may behave as laminar while gas and other low viscosity liquids show turbulent behaviour. Accordingly, correct modelling of the turbulence, including correct transitional behaviour between turbulent and laminar flow becomes of great importance. In this paper we have investigated two phase flows of gas at a rather high density and viscous oil. Experiments have been performed at the SINTEF Multiphase Flow Laboratory at Tiller, Trondheim. The experimental section was horizontal, with a pipe inner diameter of 69 mm. Pressure drop - and liquid hold-up time series, as well as video-documentation of the flow, were recorded. The experiments have been analysed and simulated by the Quasi-3D flow model which has been developed in the LedaFlow development project. The results show that flow regimes are well predicted, as well as liquid fractions (hold-up) and pressure drops. Furthermore, some cases have been identified where the Quasi-3D concept is challenged and where the full 3D effects need special attention and modelling. In the paper we describe the experiments in more details, discuss the general challenges on viscous flow modelling, present the special features of our Quasi-3D flow model and compare predictions to the experimental results. Finally we discuss the perspectives of multidimensional modelling as a virtual laboratory for multiphase pipe flows comprising viscous liquids.ACKNOWLEDGEMENTS.The financial support to the Leda Project, the long-time contributions from the Leda Technical Advisory Committee, as well as permission to publish, by Total, ConocoPhillips, and SINTEF are all gratefully acknowledged. Our colleagues Ernst Meese, and Runar Holdahl (SINTEF), Wouter Dijkhuizen and Dadan Darmana (Kongsberg Oil & Gas Technologies), Harald Laux (OSRAM Opto Semiconductors GmbH, Regensburg), and Alain Line (INSA, Toulouse) are acknowledged for their contributions to the development.publishedVersio

Simulation of two-phase viscous oil flow

Multiphase flows of heavy oils and other fluids with high apparent viscosity is a particular industrial challenge. Main challenges here is that interfacial waves, atomization at the large scale gas–liquid interface as well as bubble entrainment and separation all are significantly modified by high fluid viscosity. In addition the viscous liquid may behave as laminar while gas and other low viscosity liquids show turbulent behaviour. Accordingly, correct modelling of the turbulence, including correct transitional behaviour between turbulent and laminar flow becomes of great importance. In this paper we have investigated two phase flows of gas at a rather high density and viscous oil. Experiments have been performed at the SINTEF Multiphase Flow Laboratory at Tiller, Trondheim. The experimental section was horizontal, with a pipe inner diameter of 69 mm. Pressure drop - and liquid hold-up time series, as well as video-documentation of the flow, were recorded. The experiments have been analysed and simulated by the Quasi-3D flow model which has been developed in the LedaFlow development project. The results show that flow regimes are well predicted, as well as liquid fractions (hold-up) and pressure drops. Furthermore, some cases have been identified where the Quasi-3D concept is challenged and where the full 3D effects need special attention and modelling. In the paper we describe the experiments in more details, discuss the general challenges on viscous flow modelling, present the special features of our Quasi-3D flow model and compare predictions to the experimental results. Finally we discuss the perspectives of multidimensional modelling as a virtual laboratory for multiphase pipe flows comprising viscous liquids

Repeatability in a multiphase pipe flow case study

A high degree of repeatability is most often an underlying assumption for research and development based on multiphase flow experiments. In this paper repeatability in multiphase flow experiments are studied through an experimental campaign with 28 replicates for 11 unique settings. The experiments were conducted in a flow loop with multiple injections of oil, water and air. A high degree of repeatability was found, with relative replicate deviations in volume flow rates and pressure drops of 0.1% in magnitude. Further, several potential causes of replicate deviations were studied, and firmer control of temperature of the inflow fluids is proposed as a means to improve repeatability in volume flow rates and pressure. We conclude that for practical use, the presented category of multiphase experiments sufficiently meets underlying repeatability assumptions

Repeatability in a multiphase pipe flow case study

A high degree of repeatability is most often an underlying assumption for research and development based on multiphase flow experiments. In this paper repeatability in multiphase flow experiments are studied through an experimental campaign with 28 replicates for 11 unique settings. The experiments were conducted in a flow loop with multiple injections of oil, water and air. A high degree of repeatability was found, with relative replicate deviations in volume flow rates and pressure drops of 0.1% in magnitude. Further, several potential causes of replicate deviations were studied, and firmer control of temperature of the inflow fluids is proposed as a means to improve repeatability in volume flow rates and pressure. We conclude that for practical use, the presented category of multiphase experiments sufficiently meets underlying repeatability assumptions

Repeatability in a multiphase pipe flow case study

A high degree of repeatability is most often an underlying assumption for research and development based on multiphase flow experiments. In this paper repeatability in multiphase flow experiments are studied through an experimental campaign with 28 replicates for 11 unique settings. The experiments were conducted in a flow loop with multiple injections of oil, water and air. A high degree of repeatability was found, with relative replicate deviations in volume flow rates and pressure drops of 0.1% in magnitude. Further, several potential causes of replicate deviations were studied, and firmer control of temperature of the inflow fluids is proposed as a means to improve repeatability in volume flow rates and pressure. We conclude that for practical use, the presented category of multiphase experiments sufficiently meets underlying repeatability assumptions.publishedVersio

Mn-alginate gels as a novel system for controlled release of Mn2+ in manganese-enhanced MRI

The aim of the present study was to test alginate gels of different compositions as a system for controlled release of manganese ions (Mn2+) for application in manganese‐enhanced MRI (MEMRI), in order to circumvent the challenge of achieving optimal MRI resolution without resorting to high, potentially cytotoxic doses of Mn2+. Elemental analysis and stability studies of Mn‐alginate revealed marked differences in ion binding capacity, rendering Mn/Ba‐alginate gels with high guluronic acid content most stable. The findings were corroborated by corresponding differences in the release rate of Mn2+ from alginate beads in vitro using T1‐weighted MRI. Furthermore, intravitreal (ivit) injection of Mn‐alginate beads yielded significant enhancement of the rat retina and retinal ganglion cell (RGC) axons 24 h post‐injection. Subsequent compartmental modelling and simulation of ivit Mn2+ transport and concentration revealed that application of slow release contrast agents can achieve a significant reduction of ivit Mn2+ concentration compared with bolus injection. This is followed by a concomitant increase in the availability of ivit Mn2+ for uptake by RGC, corresponding to significantly increased time constants. Our results provide proof‐of‐concept for the applicability of Mn‐alginate gels as a system for controlled release of Mn2+ for optimized MEMRI application