Abstract
For Carbon Capture and Storage (CCS) systems, accurate multiphase flow predictions are important to achieve safe and cost-effective design and operation. The multiphase flow simulator LedaFlow was originally developed for hydrocarbon production systems, but due to the rapid emergence of CCS technology, LedaFlow is currently being adapted to scenarios and conditions relevant for CO2 injection.
In CCS applications, the gas/liquid density difference tends to be smaller than in typical hydrocarbon production systems, and the gas/liquid surface tension can also be very small. Both these factors increase the degree of gas bubble entrainment into the liquid, and measurements show that the gas bubble fraction in the liquid film can become very high in stratified two-phase flows with CO2. In LedaFlow, bubble entrainment in stratified flows is presently not modelled because the overall effect of bubble entrainment on typical oil/gas scenarios is usually limited. It has however become clear that bubble entrainment needs to be included in LedaFlow to accurately model CO2-rich flows.
This paper outlines the derivation and implementation of a new gas entrainment model in LedaFlow for stratified flows in near-horizontal pipes. The model is based on a balance between turbulent diffusion and gravitational drift, mainly using validated closure laws from public literature. The bubble size model was calibrated by fitting the model to experimental bubble concentration profiles in bubbly flows. Comparisons between the model predictions and the respective measurements show very good agreement with the bubble entrainment data for data covering several different pressures and two different pipe diameters. Furthermore, we observe that the flow regime predictions improve with the introduction of the new gas entrainment model in LedaFlow.
In CCS applications, the gas/liquid density difference tends to be smaller than in typical hydrocarbon production systems, and the gas/liquid surface tension can also be very small. Both these factors increase the degree of gas bubble entrainment into the liquid, and measurements show that the gas bubble fraction in the liquid film can become very high in stratified two-phase flows with CO2. In LedaFlow, bubble entrainment in stratified flows is presently not modelled because the overall effect of bubble entrainment on typical oil/gas scenarios is usually limited. It has however become clear that bubble entrainment needs to be included in LedaFlow to accurately model CO2-rich flows.
This paper outlines the derivation and implementation of a new gas entrainment model in LedaFlow for stratified flows in near-horizontal pipes. The model is based on a balance between turbulent diffusion and gravitational drift, mainly using validated closure laws from public literature. The bubble size model was calibrated by fitting the model to experimental bubble concentration profiles in bubbly flows. Comparisons between the model predictions and the respective measurements show very good agreement with the bubble entrainment data for data covering several different pressures and two different pipe diameters. Furthermore, we observe that the flow regime predictions improve with the introduction of the new gas entrainment model in LedaFlow.