Safer Dual-Functional Gas Hydrate Dissolver and Inhibitor to Replace Methanol

Abstract

In the presence of free water and under certain conditions of temperature and pressure, low-molecular-weight gases such as methane and ethane present in the fluid stream flowing in pipelines cause the formation of gas hydrate crystals. These gas hydrate crystals may accumulate and cause a partial or complete plugging of pipelines in the vertical or horizontal section. Methanol has been used in the industry as an effective gas hydrate dissolver and inhibitor, but its low flashpoint temperature makes it unsafe to be stored and pumped in large volumes. The objective of the current work is to develop a safer dissolver and inhibitor for gas hydrate plugs that form in pipelines. Methanol has a very low freezing point (−90 °C) and it is completely miscible with water, which can shift the hydrate phase equilibrium to lower temperatures. Solvent- and aqueous-based formulations were selected as alternatives to methanol, keeping in mind parameters such as higher flashpoint, miscibility with water, freezing point, viscosity, and local availability. The performance of these formulations was evaluated in a see-through gas hydrate reactor. Representative gas and water compositions were used in the experiments to form the gas hydrate inside the reactor. Hydrate formation was detected by the change in torque or by visual inspection through the see-through window of the reactor. Methanol was able to mobilize the hydrate plug when used at 10 vol %, while complete dissolution was achieved at 30 vol %. In comparison, the potassium formate saturated solution achieved complete dissolution of the hydrate plugs at 10 vol % in a lesser time compared to methanol. The tested formulations worked not only as a dissolver but also as an inhibitor to prevent the formation of hydrates once they are melted or dissolved. These formulations enable safer operations in the field and improve the performance when it comes to melting gas hydrate plugs.

Topics & Concepts