The simulation of 2 times longer of pipeline gives us an understanding of the influence of pipeline length on the appearance of severe slugging, so now we move to testing the effect of riser length.

We keep all of the characteristics of the pipeline-riser system and just change the geometry of the riser with 2 times longer as shown in the figure below.

We continue to take the same manipulation as the base case:

1. Drawing 3 turndown curve

2. Estimate the transition point in each turndown curve

3. Drawing the flow map

We do the same simulation for drawing 3 turndown curve as we did before, and compare the turndown point in these two different riser 2 times higher geometry.

Here is the table of the position (mass flow rate, pressure drop) of turndown point between two different riser length geometry.

Base case (Riser H) | Riser 2H | |

Turndown point 1 | (1.26314, 0.77) | (1.3474, 1.684) |

Turndown point 2 | (0.8634, 0.517) | (1.1512, 1.684) |

Turndown point 3 | (0.5792, 0.332) | (0.8688, 0.692) |

By comparing the turndown points for these two different riser length, it is clear that these points have a great difference. The pressure drop augments because of the riser length is higher.

The following figure gives us a distinct seeing by joining two turndown curve together.

These two turndown curves have the same tendency, but have a difference in the pressure drop. We continue to find the transition point by using the turndown curve.

- Run simulation for each transition point, however, neither of the turndown point in this riser 2H has the doubt to judge it is severe slugging or not, it is always sure that the turndown point is not severe slugging. So we directly move to the left point, and even find that the severe slugging appears at the point which is far from the turndown point.
- Export all the data in Ledaflow to Matlab and do the same comparison as the base case.
- Determine the transition point.

Here is comparison of the transition line for two different riser length, it is clear that the transition line of riser 2H moves to left, and when we check the position of transition points with the turndown points, it is obviously not, the transition point appears at the point which is far from the turndown point.

Why the transition line moves to left when compared with the base case (riser 1H)? When the riser is 2 times higher, the hydrostatic pressure of the liquid-filled riser is 2 times larger, so the pressure at the riser base needs to be augmented to break the block, which increase the gas/liquid ratio. In this way, the possibility of severe slugging reduced.