Study on the Effect of Wax on the Formation Characteristics of Methane Hydrates in Water-in-Oil Emulsion Systems

In deep-water oil and gas transportation pipelines, heavy components in crude oil such as wax can affect the formation of hydrates, and the crude oil in the pipelines usually exists in a water-in-oil (W/O) form. To investigate the formation characteristics of methane hydrates in wax-containing and wax-free W/O emulsion systems, a high-pressure stirred cell was employed to study the effects of temperature, pressure, rotation speed, Span80 content, and water cut on the gas consumption and growth rate of hydrate formation. The experimental results show that with the increase in pressure, rotation speed, and water cut, both the gas consumption and maximum growth rate of hydrate formation increase monotonically. As the temperature decreases, the gas consumption of hydrates first increases and then decreases, while the maximum growth rate of the wax-free system increases monotonically. With the increase in Span80 content, the gas consumption of hydrates in the wax-free system first increases and then decreases, whereas the maximum growth rate in the wax-containing system shows a gradual decreasing trend. By comparing the gas consumption and maximum growth rate of hydrates in wax-containing and wax-free systems under different conditions, it is indicated that the presence of wax generally promotes the formation and growth of hydrates. However, under conditions of lower temperature, pressure, and water cut, this promotional effect weakens and may even turn into an inhibitory effect.