Depressurization is regarded as the most effective process for gas recovery method from the viewpoints of gas productivity and economical efficiency, compared with the other in-situ dissociation processes of Methane Hydrate (MH) . It is necessary to develop a numerical simulator for the prediction of the gas productivity from MH reservoirs. We are currently developing a numerical simulator in which the thermal conduction, the mechanical behavior of MH sediments and the fluid migration in porous media are analytically coupled. In this study, we conducted numerical studies on laboratory-scale experiments for MH dissociation process in porous media by depressurization using the numerical simulator. In the numerical model, the distribution model was used for the thermal conductivity of MH sediment. In order to evaluate the deformation behavior of the MH sediment, the elastic model for MH sediment, which was constructed on the basis of experimental results, was newly introduced into the numerical model. Using the modified numerical model, we carried out history matching for temperature change, deformation behavior and gas and water production during depressurization experiments. The change in the temperature in the MH sediment during dissociation was reproduced considering the hydrate-saturation distribution. The deformation behavior of the MH sediment was reproduced using a value for Poisson's ratio of MH sediment according to the kind of soil. The gas-water production behavior was reproduced, optimizing the shapes of the relative permeability curves that allowed us to reproduce the fluid migration in the MH sediment. To consider the effect of capillary pressure on gas-water multi-phase flow condition, we extended linear relative permeability model by introducing indexes. From the results of history matching, it was found that the modified numerical model could reproduce the series of behaviors during depressurization.
CCS (Carbon dioxide Capture & Storage) is expected as one of most efficient methods in order to reduce the amount of exhausted CO2 into the air. In the projects, the estimation of storage volume and the assessment of CO2 trapping effect in the reservoir are necessary. The objective of this paper is to analyze the residual CO2 trapping in the porous media after the storage of CO2 in the aquifer by means of X-ray CT. The CO2 injection and successive water injection test were conducted, and the replacement and trapping process of water — CO2 was analyzed by X-ray CT method. Here, the amount of CO2 replaced in the pore during CO2 injection tests was estimated. The amount of residual CO2 trapped in the rock pore during successive water injection tests was also estimated, and relations between the replaced/trapped CO2 and the porosity distribution of rock were discussed. It was found that more CO2 was stored at the relatively high porosity region, and that the residual ratio at the high porosity region easily decreased during the water injection process. However, it was also found that the approximately 10 % of injected CO2 was still remained after the six to ten times pore volume of water was injected into the rock sample.
The advection in the crack and the diffusion from the crack surface to rock matrix of contaminated materials in a rock mass are one of the important factors to evaluate the characteristics of the rock mass as a natural barrier function for a radioactive waste disposal project. In this study, X-ray CT method was applied to evaluate the advection in the crack and the diffusion of solute from the crack surfaces to the rock matrix. In order to visualize advection and diffusion phenomena, the tracer migration tests have been applied to the porous sandstone and the tracer migration and diffusion process was visualized by X-ray CT scanner. In order to evaluate density distribution in the crack and pores in the rock matrix, advanced coefficient of tracer density increment was defined. In this study, the relations between the flow in the crack and the amount of the diffused tracer into the rock matrix were discussed. The influences of the crack aperture to the tracer diffusion process were also discussed.
The bond characteristics considering the effects of embedding angle and length were investigated by pullout tests. Four polyolefin (PO) fibers were evaluated together with a steel fiber and a polyvinyl alcohol (PVA) fiber. Bond strength or the maximum pullout resistance of the steel fiber were several times higher than the other fibers, however, after the peak strength its pullout resistance decreased very rapidly. Bond strength of all six fibers increased from 0 to 45 degrees of embedding angle and thereafter decreased with increase of embedding angle. A very simple model was proposed to explain the effect of embedding angle on bond strength and it was found that the model has much potential to trace the tendency (increase and decrease) of the bond strength. The effects of embedding length were also investigated. It was found that the averaged bond strength of fibers except PVA fiber decreased with embedding length. On the other hand, the bond strength of PVA fiber did not show apparent decrease with the embedding length, which might be attributed to the coincidence of rigidity between the fiber and the matrix (mortar) .
In this study, first, a finite element analysis was performed for heterogeneous rocks or a homogeneous rock with a mountain/valley on the surface, to know the effects of the mechanical heterogeneity and the surface topography on the surface tilt induced by groundwater flow. Next, an inverse analysis was performed by using the surface tilts obtained for the rocks to estimate groundwater flow under the assumption that the rock mass is a homogeneous half space. The surface tilt in a two-layered rock is greater than that in a homogeneous rock since the vertical deformation at upper depths of the field of groundwater flow is greater than that in the homogeneous rock, to compensate the vertical deformation at lower depths, which is suppressed by the lower layer with higher Young’s modulus. The surface tilt of the rock with a mountain/valley on the surface is smaller/greater than that in a homogenous rock, depending on the distance of the surface to the field of groundwater flow. The surface tilt suddenly decreases beyond a fault since the fault absorbs the volumetric strain induced by the groundwater flow. Although groundwater flow is roughly estimated by the inversion of the tilt data obtained for the heterogeneous rocks under the assumption that the rocks are a homogeneous half space, groundwater flow may be overestimated or underestimated, and furthermore small artifacts appear around the real field of groundwater flow, depending the degree of heterogeneity, the roughness of the surface and the layout of the tiltmeters.
Using joint elements for a mechanical model of grain boundaries, we performed a preliminary 3D finite element analysis of uniaxial tensile fracture for specimen models of monomineral polycrystalline rock under the assumption that fracturing occurs only at the grain boundaries. The specimen models were created on a computer by the method previously proposed by the authors, and the constitutive law of the grain boundaries was derived by applying the associated flow rule in the plastic theory and a tension-shear-softening curve to an extended Coulomb criterion. Tensile fracturing initiates at grain boundaries with a small angle of the normal direction relative to the loading axis, which are followed by grain boundaries with a larger angle of the normal direction. Unloading of intergranular cracks occurs before the peak strength when the intergranular cracks do not compose the final failure plane that is completely formed near the inflection point of the axial stress-axial strain curve after the peak. During the completion of the final failure plane, the conversion of failure mode from tension to shear occurs at intergranular cracks that have a large angle of the normal direction relative to the loading axis. For these intergranular cracks, the axial displacement given at an end of the specimen is converted to a shear displacement, rather than an opening displacement, and the normal stress becomes to be compressive due to shear dilation. Furthermore, the number of tensile intergranular fracturing at the peak strength increases with a decrease in the constant α that characterizes the rate of decrease in the tensile strength in the tension-shear-softening curve of the grain boundaries, and as a result, the tensile strength of the rock specimen increases with a decrease in the constant α. However, the effect of the residual frictional coefficient is small and limited to the stage after the final failure plane is completely formed, since the residual friction coefficient affects the mechanical behavior of the grain boundaries only after the failure plane is completely formed.
Cobalt-rich ferromanganese crusts (cobalt crust) contain strategic metals such as copper, nickel and cobalt. In order to recover cobalt, the reduction and dissolution of manganese oxide in crusts is required because cobalt is interlocked in manganese oxide. It is known that galvanic interactions between metal sulfide minerals and manganese nodule cause oxidation-reduction reactions on them. In this study, galvanic leaching of chemical analytical MnO2 and cobalt crust has been examined in the presence of pyrite. The measurement of rest potential indicated that MnO2 was nobler than pyrite. The dissolution of the MnO2 was accelerated in the presence of pyrite because MnO2 could act as cathode to be reduced in the galvanic couple MnO2/FeS2 . The dissolution of manganese and cobalt from the cobalt crust was enhanced in the presence of pyrite, and 84% of cobalt was extracted in three days while about 1% in the absence of pyrite in sulfuric acid solution of pH0.8. The leaching of the cobalt crust has been studied under various experimental parameters such as pH, amount of pyrite and particle size.
It is demanded more convenient survey methods for soil pollution by oils and techniques for toxicity evaluation of petroleum hydrocarbons. The quantitative bioassay using luminous bacteria has not been established. The accumulation of data obtained under scientific condition setting is required. Firstly, methanol, ethanol and n-propanol which are both moderate hydrophilic and oleophilic, were examined whether they are adequate as the extraction solvent for soil polluted by oils. From the results in bioassay test using luminous bacteria, methanol was selected as the most suitable extraction solvent from them. Secondly, the acute toxicity evaluation and the detection limit of gasoline, heating oil, light oil, benzene, toluene, n-hexane and carbon disulfide were experimentally examined. The severity of toxicity on luminous bacteria by each 100 vol% of them (without solvent) except n-hexane was carbon disulfide > toluene > gasoline > benzene > methanol > heating oil > light oil. Although the toxicities of 100 vol% of heating oil, light oil and n-hexane were weaker than that of methanol, the use of methanol as the solvent improved the detection sensitivity for them and was possible to detect the toxicity of them by luminous bacteria. The appropriate reaction time for toxicity evaluation or screening may be 15 to 45 minutes. The severity of toxicity on luminous bacteria evaluated using methanol solvent was gasoline > n-hexane > heating oil > toluene > carbon disulfide > benzene > light oil. Also, this study showed potential for quantitatively evaluating in the ranges of 0.02 to 1 vol% of gasoline and heating oil, 0.1 to 5 vol% of light oil and carbon disulfide, 0.2 to 5 vol% of benzene, 0.1 to 1.0 of toluene and 0.05 to 0.5 vol% of n-hexane in methanol solvent (extractant).
The surface of a conventional sanitary ware was covered with the glaze that was a glassy phase containing silica and zircon crystals. Therefore, the surface of the glassy region was eroded selectively by using it for long time, which made a rough surface of a sanitary ware that causes adhesion of dirt on the surface. In this study, we investigated a double layer structure constituted of a conventional graze layer and a coating glass layer on the sanitary ware surface for improvement of durability and anti-contamination of the sanitary ware. We selected seven glasses constituted of SiO2-Al2O3-CaO-MgO-K2O-Na2O system for the coating glasses on the conventional glaze layer, and fabricated a double layer structure on a sanitary ware by firing. We also investigated the physical properties (glass transition temperature Tg, crystallization temperature Tc, liquidus temperature T1, and viscosity of the glass melts (η)) of the coating glass were measured. The microscopic observations of the cross-section at the interface between the graze layer and the coating glass layer showed three different mixing patterns as follows. (1) The graze layer and the coating glass layer were completely separated. (2) The graze layer and the coating glass layer were partially mixed. (3) The graze layer was partially exposed to the surface of the coating glass layer. From the results of the physical properties measurements of the coating glasses, it was found that the formation of double layer structure was controlled by the viscosity of glass melts and the thickness of the coating glass layer. Finally, we concluded that the accomplished double layer on the sanitary ware surface was suitable for improvement of durability and anti-contamination.
The lamination interface generated by a power outage during the electrorefining of copper using a wax-less permanent-cathode was investigated to elucidate the formation mechanism of the interface. X-ray diffraction, X-ray photoelectron spectroscopic measurements and electrochemical quartz crystal microbalance measurements revealed that the interface is composed mostly of CuCl (s) . Based on the thermodynamics of aqueous solution containing copper ions and chloride anions, it is considered that Cu+ ions are spontaneously generated through the reaction Cu + Cu2+ → 2Cu+ at the surface of the copper cathode, resulting in the deposition of insoluble CuCl (s) . Circulation of electrolyte during the power outage could suppress the accumulation of Cu+ ions in the vicinity of the cathode and minimize the formation of CuCl (s) layer, which makes the lamination interface after recovery from the power outage.