Jakyung Kim

Synergistic Hydrate Inhibition of Monoethylene Glycol with Poly(vinylcaprolactam) in Thermodynamically Underinhibited System

This study investigates the hydrate inhibition performance of monoethylene glycol (MEG) with poly(vinylcaprolactam) (PVCap) for retarding the hydrate onset as well as preventing the agglomeration of hydrate particles. A high-pressure autoclave was used to determine the hydrate onset time, subcooling temperature, hydrate fraction in the liquid phase, and torque changes during hydrate formation in pure water, 0.2 wt % PVCap solution, and 20 and 30 wt % MEG solutions. In comparison to water with no inhibitors, the addition of PVCap delays the hydrate onset time but cannot reduce the hydrate fraction, leading to a sharp increase in torque. The 20 and 30 wt % MEG solutions also delay the hydrate onset time slightly and reduce the hydrate fraction to 0.15. The addition of 0.2 wt % PVCap to the 20 wt % MEG solution, however, delays the hydrate onset time substantially, and the hydrate fraction was less than 0.19. The torque changes were negligible during the hydrate formation, suggesting the homogeneous dispersion of hydrate particles in the liquid phase. The well-dispersed hydrate particles do not agglomerate or deposit under stirring. Moreover, when 0.2 wt % PVCap was added to the 30 wt % MEG solution, no hydrate formation was observed for at least 24 h. These results suggest that mixing of MEG with a small amount of PVCap in underinhibited conditions will induce the synergistic inhibition of hydrate by delaying the hydrate onset time as well as preventing the agglomeration and deposition of hydrate particles. Decreasing the hydrate fraction in the liquid phase might be the reason for negligible torque changes during the hydrate formation in the 0.2 wt % PVCap and 20 wt % MEG solution. Simple structure II was confirmed by in situ Raman spectroscopy for the synergistic inhibition system, while coexisting structures I and II are observed in 0.2 wt % PVCap solution.

Effect of kinetic hydrate inhibitor and liquid hydrocarbon on the heterogeneous segregation and deposition of gas hydrate particles

Segregation and deposition of hydrate particles observed in flowloop experiments are required to be investigated more thoroughly to understand the hydrate plugging mechanism in offshore flowlines. We used natural gas as gas phase and selected three different systems as liquid phase, which are pure water only, kinetic hydrate inhibitor added aqueous solution, and water+decane mixture, respectively. Hydrate formation process including onset and growth was studied by measuring the pressure, temperature, and torque changes in high-pressure autoclave. The obtained results suggest that poly-vinyl caprolactam (PVCap) solution shows elongated growth period than pure water until distinct torque change is observed, which also indicates the suppressing effect of PVCap on the growth of hydrate crystals. However, the presence of decane as continuous liquid phase enhances the deposition of hydrate particles on the wall. The torque change with conversion to hydrate used in this study is found to be useful to classify the hydrate formation process into three different regions.

Optimization of MEG Injection and Regeneration System for Offshore Gas Fields Using Multiphase Simulation and Synergistic Inhibition Strategies

Industry has been relying on the injection of considerable amount of Mono Ethylene Glycol (MEG) for hydrate inhibition in petroleum production systems, especially in offshore gas wells. However current design of MEG injection and regeneration systems is used to be over-sized as it consider the worst operation conditions such as shut-in pressure, ambient seawater temperature, and maximum water production rate. Recently, multiphase simulation tools have been widely used to estimate the temperature and pressure profiles of offshore flowlines for both steady-state and transient operations, which would be useful to better estimate the worst operation conditions of offshore flowlines. Moreover, recent research [1] results on synergistic inhibition suggest that MEG injection rate might be reduced below the required concentration by adding small amount of Kinetic Hydrate Inhibitors (KHI). Here we carried out an experiment to validate the effect of using synergistic inhibition with MEG and KHI on the design of MEG injection and regeneration systems for offshore gas wells. The studied concentration range of MEG is up to 30 wt% and PVCap concentration is between 0.1 and 1.0 wt%. Synthetic natural gas composed of C1 90 mol%, C2 6 mol%, C3 3 mol%, and nC4 1 mol% is used for all experiments. High pressure autoclave system mounted with overhead stirrer is used with constant cooling method. Furthermore, multiphase simulation tool, OLGA, is used to simulate the operation conditions of offshore gas fields. The amount of condensed water and temperature-pressure profiles during extended shut-in period are calculated for 10 km offshore flowlines. The obtained results suggest that the injection rate of MEG can be reduced about 50% by adopting synergistic inhibition and multiphase flow simulation, which would reduce the CAPEX and OPEX for MEG. Moreover the reduced size of MEG regeneration unit would improve weight and space management on platform topside.Copyright