The influence of pipeline wettability and crude oil composition on deposition of gas hydrates during petroleum production

Abstract

At specific temperature and pressure conditions, hydrates can sometimes plug production pipelines. It has been shown that some oils contain natural inhibiting compounds (NICs) that prevent hydrate plug formation even though the pressure and temperature are within the hydrate formation conditions. Thus, the hydrate plugging tendency is influenced by the crude oil composition. The mechanisms by which deposition of hydrates occur in a petroleum production system are also likely to be related to pipeline surface properties, e.g. pipeline material, surface free energy and roughness. The ultimate aim of this work is to develop an understanding of the deposition of hydrates on the pipeline wall. Most of the work in this thesis deals with contact angle measurements that determine the wettability of various solids. Different materials and oil compositions have been tested including both model oil systems and crude oil systems. Micromechanical force experiments have been used to determine the adhesion force between hydrates and solids with different amounts of petroleum acids present in the oil phase. The factors that have been identified in this work as most likely influencing deposition of hydrates to the pipeline wall are the presence of free water, surface material and crude oil composition. It may seem as if hydrate deposition will not occur unless free water is present. When the pipeline wall material has a low surface free energy, such as epoxy coated surfaces, deposition seems to be reduced. Crude oils that are assumed as non-plugging and contain high concentrations of acids seems to reduce the probability for deposition to occur.