Investigation on Thermodynamic Equilibrium Conditions of Methane Hydrates in Multiphase Gas-Dominant Pipelines.

The estimation of thermodynamic equilibrium conditions of methane hydrates in the presence of crude oil based on experiments is shown in this research work. This pipeline system replicated the gas-dominant multiphase transmission pipelines at deep-sea regions. An experimental study is done by the usage of a Raman gas hydrate reactor. The pressure was maintained in the range of 3-8 MPa for the experimental study. The water cut is kept constant throughout the system as 30%. Initially, the experimental setup is calibrated by using carbon dioxide gas. Then, methane hydrates are formed with and without crude oil. The methane hydrates that are created without the presence of crude oil are validated with simulation that is performed using CSMGEM, PVTSIM software, and literature data. Then, the thermodynamic conditions are found for the methane hydrate formation in the presence of crude oil with an addition of a 15% oil cut to the system. From these results, the phase behavior of a multiphase system is evaluated. The formation of methane hydrates in the system was found to be affected by the presence of an additional oil phase that exhibited an inhibition behavior. This research validates all the multiphase systems that contain similar hydrocarbon and gas compositions.

Kinetic Behavior of Quaternary Ammonium Hydroxides in Mixed Methane and Carbon Dioxide Hydrates.

This study evaluates the kinetic hydrate inhibition (KHI) performance of four quaternary ammonium hydroxides (QAH) on mixed CH4 + CO2 hydrate systems. The studied QAHs are; tetraethylammonium hydroxide (TEAOH), tetrabutylammonium hydroxide (TBAOH), tetramethylammonium hydroxide (TMAOH), and tetrapropylammonium hydroxide (TPrAOH). The test was performed in a high-pressure hydrate reactor at temperatures of 274.0 K and 277.0 K, and a concentration of 1 wt.% using the isochoric cooling method. The kinetics results suggest that all the QAHs potentially delayed mixed CH4 + CO2 hydrates formation due to their steric hindrance abilities. The presence of QAHs reduced hydrate formation risk than the conventional hydrate inhibitor, PVP, at higher subcooling conditions. The findings indicate that increasing QAHs alkyl chain lengths increase their kinetic hydrate inhibition efficacies due to better surface adsorption abilities. QAHs with longer chain lengths have lesser amounts of solute particles to prevent hydrate formation. The outcomes of this study contribute significantly to current efforts to control gas hydrate formation in offshore petroleum pipelines.