Research into severe slugging is aimed at the reliable prediction of its occurrence and of the associated slug length, frequency, and arrival velocity, all these has been studied in our base case. And also, we know that the gas and liquid flow rate, flowline inclination, riser-foot geometry, and liquid viscosity have effect on the occurrence of severe slugging. So in this part, we focus on the influence of the pipeline length.

We keep all of the characteristics of the pipeline-riser system and just change the geometry of the pipeline 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 in the base case, and compare the turndown point in these two different pipeline length geometry.

Here is the table of the position of turndown point between two different pipeline length geometry.

Base case (Pipeline L) | Pipeline 2L | |

Turndown point 1 | (1.26314, 0.77) | (1.2228, 0.777) |

Turndown point 2 | (0.8634, 0.517) | (0.8634, 0.522) |

Turndown point 3 | (0.5792, 0.332) | (0.5792, 0.341) |

By comparing the turndown points for these two different pipeline length, it is clear that these points are basically the same.

The following figure gives us a distinct seeing by joining two turndown curve (Turndown Curve 1) together.

Although the left part of the turndown curve including the turndown point is almost the same, the transition point always need to be checked ( Turndown point =? Transition point or Transition point moves to left or right ).

- Run simulation for each transition point, if it is not severe slugging, directly move to the left point, if it is not sure, run the simulation for the left point and right 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 pipelines, it is clear that the transition line of pipeline 2L moves to the right, and when we check the transition points with the turndown points, almost all the turndown points are transition points.

Why the transition line moves to the right when compared with the base case (pipeline 1L)? Longer pipeline, which increase the gas buffer volume, and lower the gas/liquid ratio's, which reduce the pressure buildup rate in the pipeline, increase the possibility of severe slugging.