Modeling of Gas in Riser Unloading Problem

A Gas-in-Riser (GIR), when not predicted and controlled, expands and reaches the surfaces in an uncontrolled manner to cause unloading of the riser and finally a blowout, which was the case with Deepwater Horizon's 2010. Failing to predict and model GiR fluid flow would jeopardize well control. Such a model is vital for efficient performance of riser gas handling (RGH) systems, but it is still a challenge for the offshore industry. Therefore, in this work an analytical model was found for gas migration in riser with water-based muds, based on gas laws. However, the model cannot converge from a specified time/depth on. This is considered a challenge for developing a straightforward fluid flow model that can handle modeling gas flow in the riser. Therefore, this work finds an analytical model which can not only outperform iterative models but can also find the riser equilibrium depth for a real gas. Since backpressure is considered in the developed equations, it can be used for riser gas handling (RGH) systems. The root cause of inefficiency and impracticality of gas law models above the equilibrium depth is still unclear; thus, to provide a more reliable gas migration modeling it is recommended to further study the root cause and apply more sophisticated CFD methods to compare with gas laws’ results.