Displacement of liquid in pipe flow: Two-dimensional simulations

Abstract

In the oil and gas industries it is crucial to handle flow assurance in a good manner in order to ensure a safe and economical operation. In subsea areas there are challenging conditions, with high pressure and low temperature. In addition the fact that the systems are located subsea makes it more difficult to have control of it. Displacement and slugging are subjects that have been studied in this thesis. Two aspects of displacement have been considered: ? Displacement of hydrocarbons in order to avoid hydrate formation, and ? Displacement of hydrocarbons in order to avoid oil dischange to the sea during subsea intervention .

Two cases have been considered in this thesis, one displacement case conducted in collaboration with Framo Engineering, and a blow-through test that had already been conducted at the Norwegian University of Science and Technology (NTNU). The focus of this work has concerned simulations of these tests in LedaFlow 1D and LedaFlow Q3D and comparing the results with each other and with the experiments. In addition the work on this thesis also concerned conducting full scale displacement tests with Framo Engineering.

By simulating and analyzing displacement in different simulator tools, it is possible to predict the displacement and find out how to displace in a best manner, with which type of displacement medium and with which mass flow rate. In the same manner it is possible to predict slug flow, slug behavior and size. Only small variations in pipeline elevation can cause changes in slug characteristics. Therefore it is advantageous to use a simulator to predict slug flow in each pipeline.

Regarding the displacement tests, the trend with simulating in LedaFlow 1D was that it predicted lower displacement rates compared to what was the case in the experiments. When simulating the tests in LedaFlow Q3D with tuned parameters it led to high displacement levels that were very similar to the experimental displacement levels. Concerning the blow-through test simulations in both LedaFlow Q3D and with LedaFlow 1D resulted in more liquid swept out of the system than what was the case in the experiment. The inlet pressures in LedaFlow 1D and LedaFlow Q3D had about the same progress as in the experiments. The main difference was that LedaFlow 1D reached a higher peak and that the inlet pressure from the experiments decreased slower.