Experimental measurement of the induction time of natural gas Hydrate and its prediction with polymeric kinetic inhibitor

Abstract

It is assumed that the heterogeneous nucleation of hydrates in the upstream oil and gas industry occurs, which would block the fluid flow transportation, when produced fluids (oil/gas/water) in a multiphase pipeline enter the hydrate stability temperature and pressure conditions. This has led to the development of flow assurance strategies to operate outside the hydrate stability region. The past flow loop data on oil and gas systems suggest that hydrates usually require some sub-cooling (on the order of 3K or so) to be formed and it takes a while. Thus, there are two different ways to transport the fluid; firstly by staying outside of the hydrate-stable region or secondly transport the fluid in the hydrate stable region before hydrate formation started. Thus it would be also possible to transport the fluid in hydrate stability region before hydrate formation started. To achieve this goal, three different kinds of inhibitors are used: (1) thermodynamic inhibitors, (2) kinetic inhibitors, and (3) anti-agglomerants. Thermodynamic inhibitors would change the equilibrium condition of gas hydrates, while kinetic inhibitors would change the induction time and anti-agglomerants inhibit the crystal agglomeration. In this work, two kinetic inhibitors (poly N-vinylpyrrolidone, PVP and poly N-vinylcaprolactam, PVCap) were tested and a kinetic model to predict the induction time with an inhibitor was developed using the Freundlich adsorption isotherm. Currently, the model can be used in limited conditions such as specific gas composition, temperature range and polymeric inhibitors. However, this model has a good potential to predict the minimum concentration of inhibitor to prevent hydrate plugging at various temperatures and pressure conditions.