Session: 10-10-03: Industrial Flows - III

Paper Number: 70735

Start Time: Tuesday, 10:15 AM

70735 - A One-Dimensional Mechanistic Model for Tracking Unsteady Slug Flow 

Depending on the geometric features of the pipeline conveying a mixture of liquid (oil and water) and gas, the fluids properties, and their flow rates, the slug flow pattern — characterized by an alternate distribution of gas- and liquid-dominant phases — may prevail.  In an oil-and-gas production system, the reliability of separation and pumping equipment downstream of the pipe is known to be strongly affected by the size and dynamics of slug bodies.  Because the presence of slug flow entails the possibility of flow assurance issues, including the costs of operational interruption, the development and improvement of tools for the accurate modelling of slug flow continues to be of interest to the industry.  In particular, models capable of predicting the transient behavior of the slug units as they travel along the pipe may prove useful especially in conditions where the conduit’s vibrational motions are significant, as in the presence of resonance, or if the maximum slug length and not only the average is sought.

A novel one-dimensional slug tracking mechanistic model for unsteady, upward gas-liquid slug flow in inclined pipes is presented.  The model stems from the first principles of mass and momentum conservation applied to a slug unit cell consisting of a slug body of liquid and a region of stratified flow containing an elongated bubble and a liquid film.  The slug body front and rear are treated as surfaces of discontinuity where mass and momentum balances or ``jump laws'' are prescribed. The former is commonly applied in mechanistic models for slug flow, whereas the latter is typically overlooked, thereby leading to the assumption of a continuous pressure profile at these points or to the adoption of a pressure drop due to the fluid acceleration on a heuristic basis.  Our analysis shows that this pressure change arises formally from the momentum jump law at the slug body front.  The flow is assumed to be isothermal, the gas is compressible, the pressure drop in the elongated bubble region is accounted for, the film thickness is considered uniform, and weight effects from interface level gradients are included. Besides specifying momentum jump laws at both borders of the slug body, another novel feature of the present model is that we avoid adopting the quasi-steady approximation for the elongated bubble-liquid film region, and thus the unsteady terms in the mass and momentum balances are kept. The present model requires empirical correlations for the slug body length and the elongated bubble nose velocity.  The non-linear equations are discretized and solved simultaneously for all the slug unit cells filling the pipe.  Time-space variation of the slug body and film lengths, volume fractions, and pressures, among other quantities, can be predicted, and model performance is evaluated by comparing with data in the literature.

Presenting Author: Juan C. Padrino Newcastle University

Authors:

Juan C. Padrino Newcastle University
Narakorn Srinil Newcastle University
Victoria Kurushina Newcastle University
David Swailes Newcastle University
Christopher C. Pain Imperial College London
Omar K. Matar Imperial College London