Study on the Flow Characteristics of Methane Hydrate in the Water-Dominated Bubbly Flow

Summary Natural gas hydrate is an important alternative energy used to supplement the shortage of conventional oil and natural gas. In the production of offshore natural gas hydrates, the water drainage line in the hydrate production well faces serious hydrate plugging risk. To study the mechanism of hydrate plugging in the water drainage line, we developed a numerical model to describe the processes of hydrate agglomeration and hydrate deposition on the pipe wall. We also performed methane hydrate slurry experiments in water-dominated bubbly flow to validate the developed numerical model. We found that hydrate particles would accumulate under low-velocity conditions and induce hydrate deposition at the inlet of the pipeline, which caused hydrate plugging risk near the entrance of the pipeline. Although higher hydrate deposition ratios were found under high-velocity flow conditions, the hydrate particles would distribute more uniformly and spread widely in the whole pipeline, whereas most of the hydrate particles tended to flow at the middle of the pipeline. The agglomeration and deposition of hydrate particles obviously disturb the flow velocity field and increase the turbulent kinetic energy. Comparisons between simulation results and experimental data show that the maximum discrepancy is 35.73% at a flow velocity of 2.16 m/s and the minimum discrepancy in pressure drop is 4.47% at a flow velocity of 1.85 m/s. The average pressure drop discrepancy is about 20.35%. This developed numerical model exhibits reasonable agreements with experimental data. This study provides a theoretical basis for predicting hydrate plugging in the water drainage line of an offshore natural gas hydrate production system.