Three‐Dimensional Flow Characteristics of Gas–Liquid–Solid Three‐Phase Flow in Mining Riser of Horizontal Well for Gas Hydrate Extraction

ABSTRACT To address the challenges of multiphase flow inside the mining riser of deep‐sea natural gas hydrates, a three‐dimensional simulation model of gas–liquid–solid three‐phase flow in the mining riser of a horizontal well is established for deep‐sea hydrate. A test system is developed for gas–liquid–solid three‐phase flow in the hydrate mining riser using a similar principle. The experimental results are compared with numerical simulations, and the comparison accuracy is over 90.8%. The accuracy and effectiveness of the theoretical model are verified. Based on this, the effect of particle size, gas–liquid–solid ratio, and injection flow velocity on the multiphase flow transport characteristics and flow field‐riser wall collision force are investigated. The results indicate that as the particle size increases, the overall gas and liquid phase velocities do not change significantly. In the radial direction, the velocities increase from near the wall to the center of the riser. However, the solid‐phase velocity decreases with increasing particle size, while the gas‐phase volume fraction decreases. In contrast, the liquid‐phase volume fraction increases, the solid‐phase concentration decreases, and the collision force on the riser wall becomes stronger. As the gas phase proportion increases, the velocity of the gas and liquid phases also increases, with the radial direction increasing from near the wall toward the center of the riser. The velocity of the solid phase decreases as the proportion of the gas phase increases. There is no clear trend in the volume fractions of the gas and liquid phases, but the concentration of the solid phase increases with the gas phase volume fraction, also increasing the collision force. In the actual mining project, a higher flow velocity should be selected, which can not only improve the transportation efficiency, but also effectively prevent the wear of the mining riser caused by the collision of particles on the riser wall. The research results can effectively guide the safe extraction of deep‐sea natural gas hydrates.