Kiyoshi Higuchi

Behavior of CO2 Hydrate Growth below Melting Point of Ice-Research on formation and dissociation of gas hydrates.

The mining systems of methane hydrate reservoirs using CO2 hydrate are proposed, i.e. the artificial block system and the CH4-CO2 replacement system. In order to accomplish the concepts, it is necessary to understand the mechanism of formation kinetics of gas hydrates. There are few experimental data on the growth rate of CO2 hydrate, particularly in the temperature range below melting point of ice, and the mechanism has not been well understood.In this study, two types of experiments were carried out on formation kinetics of CO2 hydrate below melting point of ice, using Raman spectrometry and gas consumption method.Spectra of CO2 trapped in the hydrate cages were directly observed by Raman spectrometry. The result showed the amount of CO2 molecules increased with time, and increasing rates depend on the temperature and pressure conditions. From the experiment of gas consumption method, it was found that the growth rate of CO2 hydrate has two stages. It is indicated that the first stage of growth is rapid growth mode caused by quasi-liquid-layer or locally melted water by the latent heat, and then the latter stage is slower growth mode between gas and ice. In the temperature range of-5 ∼-1 °C, more than 40 % of total reaction gas was consumed in the first stage of growth. Considering that the reaction at the first stage is similar to that of H-LW-V system, an empirical equation was applied to the experimental results. Reaction coefficients in the first stage were estimated to determine the growth of CO2 gas hydrate. From these results, we address that proper use of the first stage growth of CO2 gas hydrate is important to develop the advanced mining systems for methane hydrate.

Estimation of Coal Bed Methane Content in Coal Seams.

Various methods of estimation of methane gas content in coal seams have been developed. The direct method of the US. Bureau of Mines is popularly used in the United States, Australia and Europe. Other methods were proposed by French National Coal Institute and German Mine Ventilation Institute. In this paper, the measurement results of some Japanese coal seams based on the measurement method of US. Bureau of Mines are described. Lost Gas were estimated by three methods which are, √t equation, Aieys equation and Darcys equation. In results by three equations, the highest value was one estimated by Aierys equation. The lowest value was estimated by Darcys equation. It can be concluded that the best estimation method of Lost Gas is the method by Aierys equation, though it is impossible to estimate the Lost Gas of some coal samples. Therefore, Lost Gas should be estimated by Aierys equation and √t method. If measurement of desorbed gas can be done several times in the initialstage, the value estimated by√t method will be approximately equal to one estimated by Aierys equation.

Problems on the Development of Some Machines assisted by Water-Jets in Japanese Coal Mines

In Japan, the development for water-jet cutting machines has been carried out mainly by The Coal Mining Research Center since 1970. A new development program was started in 1980. Some machines assisted by water jets were developed namely, a Road-header, a Coal Excavator and a drilling machine to enlarge boreholes. Practical testing of machines was carried in Japanese coal mines. Only enlarged borehole drill machine is currently being use in the coal mine.