A system for recovery of methane hydrate from the deep ocean floor has not been established. As one possible recovery system, a gas-lift system was investigated. Experiments were performed with a gas-lift system of 5 m height and 100 mm in diameter to determine the relationship between injected gas quantity and pumped water quantity. Vertical flow in the gas-lift pipe was calculated with a compressible one-dimensional two-fluid model to analyze flow in the recovery pipe of methane hydrate from the deep ocean floor. Basic equations were mass conservation equations and momentum conservation equations of each phase, the relation of volume fractions and the state equation of the gas phase. The calculation showed that optimal gas injection depths exist. Thus, the gas-lift system can be economically effective the recovery of methane hydrate from the deep ocean floor.

Methane hydrate is expected as domestic energy resources in near future in Japan. Especially the shallow-type methane hydrate and the associated methane plume are regarded as sustainable energy resources. In this paper, the investigation of the methane hydrate particle motion in the methane is presented. A quantitative analysis of the motions of the ascending methane hydrate particles seeping from the seafloor and reproduced by the numerical simulation is performed by the two-dimensional motion analysis technique and the behavior is discussed in detail.

Traditionally, it has been challenging to observe phenomena inside porous media due to their optical opacity, and the description has relied on the volume-averaged Darcy law. Recent advances in measurement techniques, such as X-ray computer tomography (CT) allow us to observe the pore structure of porous media and the multiphase flow occurring in the interior at the pore scale. In this paper, the author introduces some of the phenomena revealed by pore-scale measurements, focusing on our research on carbon dioxide capture and storage (CCS) and enhance oil recovery (EOR). Numerical simulation, which plays a leading role in digital locking technology, is omitted, but the complementary use of measurement and simulation is expected to accelerate our understanding of the phenomena. Cross-scale approaches are currently being vigorously pursued, ranging from phenomenological descriptions of Darcy law at the macroscopic scale to Navier-Stokes equation-based descriptions on the pore scale.

The objective of this study is to elucidate the formation and growth behavior of CO₂ hydrate. Based on hydrate film thickness measurements, the process of hydrate film development was classified into "formation" and "growth". A macro-scale thickness prediction model based on mass transport was constructed for these processes. Molecular dynamics calculations were also introduced and combined with the macro-scale prediction model to construct a model capable of predicting film thickness.

The results of a three-dimensional numerical simulation of the flow through a porous media using the IB method are presented. A series of calculation results show that the flows in the pores and the wake of the porous medium are affected by the Reynolds number and pore structure. It is also shown that the fluid forces acting on each component sphere differ depending on the porosity and its location in the porous media. The time-varying characteristics of the flow velocity components in the pores of the porous media are also discussed. In addition, the energy drop in the flow direction is shown, and the amount of energy dissipation in the porous media with the different void ratios is compared. Furthermore, the distributions of shear velocity are presented, and the mechanisms of the energy dissipation of the porous media flow are discussed.

We measured counter-current flow limitation (CCFL), pressure gradient dP/dz, and void fraction α_G in a 40 mm diameter vertical pipe with the rounded top and bottom ends and working fluids of air and water under flooding conditions, and we obtained the wall and interface friction factors, f_w and f_i. We compared CCFL, dP/dz, α_G, f_w and f_i with those obtained from our previous experiments in the vertical pipes with the rounded top and sharp-edged bottom ends, and the sharp-edged top and rounded bottom ends. As a result, the shape of the upper end affected flow characteristics in vertical pipes under flooding conditions stronger than the shape of the lower end did. f_w was expressed by the correlation for single-phase flows in the region of a large liquid Reynolds number Re_L, but was much larger than that from the f_w correlation for single-phase flows in the region of a low Re_L. Therefore, we obtained a f_w correlation for the region of the low Re_L as a function of Re_L or the liquid Kutateladze number K_L*, and we evaluated uncertainty of liquid volume fraction α_L = 1－α_G when α_G was obtained from the f_w correlation and dP/dz data.