An investigation on the variation of induction process in natural gas hydrate formation influenced by multiphase flow in a visual flow loop

•The variation of induction process was studied in hydrate formation in a visual flow loop.•The initial pressure is inversely proportional to the hydrate formation induction time and reaction time.•With the increase of the flow rate, the hydrate formation induction time and reaction time are shortened, but there is a flow rate threshold.•With the increase of inclination angle, the induction time tends to shorten and the reaction time generally prolongs. One of the primary issues with natural gas transportation assurance is pipeline obstruction due to the formation and deposition of gas hydrates. Thus it is crucial to study the prevention and control methods of natural gas hydrateformation. A high-pressure visual flow loop was established in this study to investigate the effects of pressure, liquid velocity, and loop inclination angle on the formation of natural gas hydrates, hydrate slurry flow and morphology. For the formation of hydrates, it was demonstrated that the pressure was inversely related to the induction time and formation time. As the initial pressure increases, the conversion rate of water increases, leading to poor fluidity. With the increase of liquid velocity, the conversion rate of water increases and there is a threshold liquid velocity. Compared with horizontal loop, the hydrate particles in the slope were repeatedly deposited and removed off the surface of the sedimentary layer by gravity, and some large hydrate particles in the slope section gathered near the bottom of the pipeline. The induction time shortens and the formation time prolongs as the inclination angle increases. The inclination angle shows little effect on the final conversion rate of water, but it can delay the growth of hydrates obviously.