Multiphase Transportation: A Kinetic Inhibitor Replaces Methanol to Prevent Hydrates in a 12-inc. Pipeline

Abstract

Abstract This paper describes how a kinetic inhibitor has been selected and then deployed in a gas pipeline in operation. Elf has performed a lot of research about new alternatives for hydrate inhibition in order to extend the area of multiphase transportation. Kinetic inhibitors can act at much lower concentration than thermodynamic inhibitors (alcohols). These new chemicals do not prevent the nucleation but significantly delay the growth of hydrate crystals. The duration of inhibition, which determines the chemical efficiency depends on the rate of sub-cooling. The understanding of these key parameters allows to contemplate multiphase transportation in the thermodynamic domain of hydrate formation. Within the family of kinetic inhibitors issued from research programs and proposed by manufacturers, three chemicals were pre-selected. Hydrodynamic conditions of the liquid phase were assessed on a pilot laboratory loop 1" × 22m. A lot of specific tests including compatibility with the field injected chemicals, modification of physical properties of the liquid phase were performed in order to anticipate any operational disturbance. From this test program, the overall most efficient chemical was selected. Then this chemical was injected instead of methanol during three weeks. The onshore gas pipeline 12" × 17km was continuously monitored with eight pressure transducers located along the pipeline. The conditions of deployment, hydrodynamic observations and induced consequences on the downstream process are presented. The main conclusion is that a kinetic inhibitor injected at a rate of 170l/d in a pipeline carrying 1 MSm3/d of gas (with its condensate and condensed water) replaced methanol, with sub-cooling conditions up to 8 C. P. 455