Author(s)

M. Naseer & W. Brandst¨atter

Abstract

Gas hydrates pose a problem to the flow assurance programs in the oil and gas industry. This paper highlights the mechanisms of hydrate formation in natural gas pipelines. Computational Fluid Dynamics (CFD) was used to gain insight in to the mechanisms of water vapour condensation and consequent water accumulation in the lowered sections of a gas pipeline. The pipeline temperature profile, condensation of water vapour at walls, hydrate formation and hydrate slurry rheology were modelled with user defined functions (UDF) integrated into the CFD-software Fluent. It was found that the uphill sections of gas pipelines are natural sites for water accumulation and hydrate formation. It is demonstrated that CFD is a valuable tool to understand complex physical phenomena occurring in multiphase flow problems. Keywords: natural gas, pipelines, condensation, hydrate formation, uphill sections, viscosity, nucleation, sagging sections, kinetics, macroscopic. 1 Introduction The growth of energy demand is constantly pushing the gas producers to operate at higher pressures. In the start of the twentieth century, the natural gas industry started facing the problem of unexpected pipeline blockage. It was shown in 1934 by HammerSchmidt that the blockages appearing to be ice were actually gas hydrates [1]. The gas hydrate formation in oil and gas pipelines is an undesirable situation, undermining the flow assurance programs in addition to posing threat to the personnel and equipment. Clathrate hydrates are non-stoichiometric mixtures of water and natural gas in which the gas molecules are trapped in polygonal crystalline structure made of water molecules [2]. The water molecules arrange themselves in an orderly fashion around the gas molecules, thus entrapping them.

Keywords

natural gas, pipelines, condensation, hydrate formation, uphill sections, viscosity, nucleation, sagging sections, kinetics, macroscopic