Morphology and coalescence stability of high internal phase emulsions formed in natural gas pipelines

Abstract

Deposition in natural gas pipelines is an issue of enormous economic and security consequences. In the past, corrosion products, elemental sulfur, hydrates and sand were common deposits in these pipelines. This study demonstrates for the first time the emulsion gel-like structure of deposit collected from Long Gang gas field in Sichuan, China. Rheological testing, thermal stability analysis, oil-water-solid three-phase ratio analysis, microscopic observations, and oil composition analysis were used for further investigation of the microstructure and macro-properties. The results suggest that the deposit has a water-in-oil emulsion structure with a high internal phase. It is extremely stable at room temperature but quickly separates into the water (79.1 wt%), oil (20.3 wt%), and solid (0.6 wt%) fractions at 80 °C. Resins and asphaltenes are two major components of the oil fraction, and they play an important role in deposit formation by strengthening the interfacial film between the oil and water phases. We speculate that the accumulation of deposits in pipelines is attributed to the emulsification of oilfield chemicals with water, hydrocarbons, natural minerals, and other gas well products under the influence of high temperature, pressure, and flow rate, among others. Finally, we provide a possible solution to deal with the deposit. The results reported in this study are expected to be useful in the development of pipeline cleaning techniques and in minimizing deposit formation.