Formation experiments of CO2 hydrate chimney in a pressure cell

Experimental investigations were conducted to understand the formation process of CO_2 hydrate the chimney structure by using a gas bubble emission technique in water within a pressure cell. The detailed process was video-recorded and analyzed to study the initiation and growth behavior of hydrate chimney while the cell pressure was increased and gas supply rate decreased gradually with time. In the initial stage of chimney growth, a hydrate crystal started to form in a cup shape at the gas nozzle and ascended together with gas bubbles due to mechanical weakness of the hydrate/nozzle contact. Growth of hydrate chimney occurred with supercooling of 3K(overpressure of 0.60MPa) or more, and continued until the top end was closed completely by hydrate

Rainfall infiltration simulation on embankment containing soluble material

Recently, mixtures of low-quality soil together with solidification materials, such as cement or steel slag, have been used for earthmoving construction. Solidification materials can improve consistency, shear strength, stiffness, and other parameters of low-quality soil by generating bonding forces between soil particles and changing grain size gradation. However, these solidification materials also contain chemical agents. In this study, simulations of rainfall infiltration into embankment constructed with the soil-solidification material mixture are conducted using the soil/water/air/soluble material coupled finite element analysis code, DACSAR-MP_ad. This analysis code can express not only deformation and seepage for an unsaturated earth structure but can also concurrently model the dispersing behaviour of soluble material. Herein, permeability and rainfall intensity conditions are provided and their effects investigated. Consequently, this study succeeds in expressing different distributions of soluble materials within embankment under different rainfall conditions

Physical and thermal properties of mud-dominant sediment from the Joetsu Basin in the eastern margin of the Japan Sea

Physical properties (bulk density and porosity) and thermal properties (thermal conductivity, heat capacity, specific heat, and thermal diffusivity) of sediment are crucial parameters for basin modeling. We measured these physical and thermal properties for mud-dominant sediment recovered from the Joetsu Basin, in the eastern margin of the Japan Sea. To determine thermal conductivity, heat capacity, and thermal diffusivity, the dual-needle probe method was applied. Grain density and grain thermal properties for the mud-dominant sediment were estimated from the measured physical and thermal properties by applying existing models of physical and thermal properties of sediment. We suggest that the grain density, grain thermal conductivity, and grain thermal diffusivity depend on the sediment mineral composition. Conversely, the grain heat capacity and grain specific heat showed hardly any dependency on the mineral composition. We propose empirical formulae for the relationships between: thermal diffusivity and thermal conductivity, and heat capacity and thermal conductivity for the sediment in the Joetsu Basin. These relationships are different from those for mud-dominant sediment in the eastern flank of the Juan de Fuca Ridge presented in previous work, suggesting a difference in mineral composition, probably mainly in the amount of quartz, between the sediments in that area and the Joetsu Basin. Similar studies in several areas of sediments with various mineral compositions would enhance knowledge of the influence of mineral composition

Surface heat flow measurements in the eastern margin of the Japan Sea using a 15 m long geothermal probe to overcome large bottom-water temperature fluctuations

Accurate surface heat flow data are required for a wide range of geological and geophysical applications. However, sediment temperature measurements beneath the seafloor often involve large uncertainties owing to the influence of bottom-water temperature (BWT) fluctuations. Previous studies reported apparently negative geothermal gradients in the Joetsu Basin of the Japan Sea and suggested that BWT fluctuations disturbed sediment temperatures. To address this problem, we monitored BWTs in the Joetsu Basin over a 2 year period to determine the depth at which the influence of BWT fluctuations on sediment temperature becomes negligible. Combined with sediment thermal diffusivity data, we determined that the BWT fluctuations can disturb sediment temperatures to a depth of 2 m. We obtained heat flow values of 81–88 mW m− 2 by measuring sediment temperatures at depths > 2 m using a 15 m long geothermal probe. The measured heat flow values are inversely correlated with topography owing to the effect of topographic change on the geothermal structure near the seafloor. A two-dimensional geothermal structure model was constructed to account for the topography, yielding an estimated regional background heat flow of 85 ± 6 mW m− 2. This study provides two important guidelines for obtaining accurate surface heat flow data in marine areas with large-amplitude BWT fluctuations: (1) quantitative information regarding BWT fluctuations and sediment thermal diffusivity is required to evaluate the depth range to which BWT fluctuations affect sediment temperature; and (2) information regarding the lithology and consolidation state of seafloor sediments is required for effective penetration using a long probe