Experimental Study of the Growth Kinetics of Natural Gas Hydrates in an Oil–Water Emulsion System

In order to explore the growth kinetics characteristics of NGH (natural gas hydrate) in an oil and gas mixed transportation pipeline and ensure the safe transportation of the pipeline, with the high-pressure hydrate experimental loop, an experimental study on the growth characteristics of NGH in an oil-water emulsion system was carried out, and the effects of pressure, flow rate, and water cut on the hydrate induction time, gas consumption, consumption rate, and hydrate volume fraction were explored, and important experimental rules were obtained. The experiment was divided into three stages: in the rapid formation stage of the hydrate, the temperature and gas consumption rose sharply, and the pressure dropped suddenly. The induction time decreased with the increase of pressure, flow rate, and water cut. The induction time of 6 MPa was 86.13 min, which was shortened by 39.68% compared with the induction time of 142.8 min of 5 MPa. The induction time of 1500 kg/h was 88.27 min, which was shorter by 13.91% than that 102.53 min of 550 kg/h. The induction time of 20% water cut was 58.53 min, which was shorter by 13.99% than that 68.4 min of 15% water cut. The gas consumption and hydrate volume fraction were both increased with the increase of pressure and water cut and decreased with the increase in the flow rate. In the whole process of the formation of NGH, the consumption rate first increased and then decreased. The pressure-drop and apparent viscosity increased with the increase of hydrate volume fraction in a certain range. The sensitivity analysis of hydrate induction time based on the standard regression coefficient method showed that the initial pressure played a major role, followed by the flow rate and the water cut. Based on the sensitivity analysis of hydrate volume fraction by the gray correlation method, it was found that the hydrate volume fraction had the closest relationship with the initial pressure, followed by the flow rate and the water cut. Finally, the empirical formulas of induction time and hydrate volume fraction in an oil-water emulsion system were established.