Recently, methane hydrate is being considered as a possible next generation energy resource replacing oil and natural gas. The amount of methane hydrate is estimated to be about 6 trillion m3 in the deep seabed around Japan which is equivalent to 100 years' supply, based on the present level of natural gas consumption in Japan. In order to progress exploitation methods, in 2001, the Research Consortium for Methane Hydrate Resources in Japan (MH21 Research Consortium) was established. In the present review, the basic properties of methane hydrate and potential areas where it exists are considered and the activities of the MH21 Research Consortium are described. Methane hydrate in the Nankai trough area, which is considered to be a potential reservoir, exists in the pore spaces among sand particles cementing them and is stable under given pressure and temperature condition. Several production methods have been proposed to extract the gas from hydrates, namely, heating, depressurization and inhibitor injection methods. There are many uncertainties in the production process, especially related to changes in the physical properties of hydrate bearing sediments caused by the dissociation of hydrate. To solve such uncertainties, experimental and analytical geotechnical studies have been carried out at Yamaguchi University in particular. The mechanical properties of methane hydrate-bearing sand are explained based on the experimental findings using the low temperature and high pressure triaxial testing equipments developed by the authors. Additionally, constitutive and numerical models for methane hydrate bearing sand to simulate the behavior of sediment during methane hydrate production are presented.
Evaluation of CO2 storage capacity in water saturated reservoir rocks is very complex because various trapping mechanisms that act at different rates are involved and, at times, all mechanisms may be operating simultaneously. Thus, in terms of the water saturated reservoir rocks, a reliable estimate of CO2 storage capacity requires a thorough understanding of the mechanisms of CO2 trapping in this system. The objective of this study is to provide a fundamental knowledge about interactions among CO2, water and rock, and contributes to development of standards for CO2 storage capacity estimation in the water saturated reservoir rocks. In this experiment, CO2 sorption was measured for rock samples (quartzose arenite, greywacke, shale, granite and serpentine) , and mineral samples (quartz and albite) in a CO2 rich dense phase at 50ºC and 100ºC, and pressures up to 20MPa, the condition of which is expected to occur mostly during CO2 injection into pores of the water saturated reservoir rocks. The result obtained from the experiment exhibited a significant sorption capacity of CO2 on all of the samples. At 50ºC and 100ºC, quartzose arenite indicated largest sorption capacity among the other samples in higher pressures (>10 MPa) . Furthermore, comparison with model prediction based on the pore filling model, which assumed that pores of the rocks and minerals will be filled with CO2, suggested the importance of the sorption mechanism in the CO2 geological storage in addition to the pore-filling mechanism. The present results indicate that the sorption process may have significant and meaningful effect on the assessment of CO2 storage capacity in geological media.
Authors have proposed constitutive equations for rock based on the theory of non-linear visco-elasticity. The constitutive equations are grouped into two types: compliance or irrecoverable-strain monotonically increases with stress. In earlier studies, it was reported that both types of constitutive equations are applicable at least to the post-failure region. In this study, applicability of the constitutive equations to the pre-failure region was examined. At first, parameters were estimated from the results of unloading-reloading and alternating loading-rate tests under uniaxial compression. The calculated results with the estimated parameters were compared with the experimental results under various loading conditions. If a constitutive equation was properly selected, the equation well simulated the various time-dependent behaviors in the pre-failure region: loading-rate dependency of Young's modulus, creep and generalized relaxation where a set of parameter values was used in not only pre-failure but also post-failure region.
When the structures such as rock slopes, underground caverns for the geological disposal of high level radioactive waste and underground power plants are constructed, the potential for displacement and damage in the surrounding rock mass is increased due to stress concentration and creep phenomenon. Therefore, the long-term monitoring of rock stability for construction of rock cavern and slopes is important to maintain stability of rock structures. Recently, development of sensors that use optical fiber have expanded mainly in the field of civil engineering and, in rock and soil mechanics, since several parameters such as temperature, strain, pressure, pH etc. can be obtained by using backscattered light in optical fibers. Additionally, some important advantages using optical fiber are its high resistance to the electric insulation failure, long-term endurance and ability to transmit data over long distances. This paper describes development of a multiple-type displacement sensor using FBG, which has potential for the long-term durability and high accuracy. Laboratory tests were carried out to investigate the relational expression computed from the relationship of the variation in the Bragg wavelength, temperature and displacement. Accuracy of the prototype developed in this research is better than 0.5% or 1/100 mm. The in situ tests involving long-term monitoring using boreholes were conducted to confirm the workability and applicability of the prototype. From the results of the in situ tests, workability is equivalent to the extensometers usually used for long-term monitoring, and the displacement computed from the variation of Bragg wavelength is almost equal to the artificially induced deformation.
The Buoyancy Weighing Method is a new measurement method of particle size distribution. Using the buoyancy weighing method, we measured the particle size distributions of the spherical glass beads, standard powders standardized by Japanese Industrial Standards, magnesite and soft-burned magnesia for measuring the mineral particles. The particle size distribution of glass beads could be measured by a buoyancy weighing method. The particle size distribution of non-spherical particles, which were the silica sand, calcium carbonate (heavy), magnesite and sof-burned magnesia, could be measured using a buoyancy weighing method. The particle size distributions measured by the buoyancy weighing method were close to those measured by the other sedimentation methods and the laser diffraction/scattering method. The particle diameter could measure 5 μm in 2 h of measuring time by the buoyancy weighing method.
Presently, CCS is recognized globally as the essential option to realize the clean fossil energy usage under the climate change constraint. Especially, coal fired power generation is still major part of world total power generation supply. In order to reduce carbon dioxide emitted from coal fired power plants, not only the improvement of generation efficiency but also introduction of CCS is considered as the essential measure to secure the stable social development and enenrgy supply. In this report, present status of Japan and international discussion for CCS, R&D and demonstration of CCS and Japanese strategy for Zero emission coal fired power generation is reviewed and discussed.
In this paper, the authors review the latest situation of risk assessment research efforts on to "Carbon Dioxide Geological Storage (geological CCS)" technology. After publication of the special report on geological CCS (2005) with sections about risk assessment, significant progresses have been achieved in risk assessment as technological evaluation of geological CCS as one of likely greenhouse gas discharge reduction measure. Those efforts produced permission scheme or safety guideline for geological CCS in some countries. On the other hand, as regard with research and development for precise risk assessment and management of CO2 Geological Storage, it is on the halfway of establishing methodologies. To establish quantitative assessment methodology for rational and reasonable risk governance of this field, the following additional research and development efforts are still urgently required: hazard data collection, data preparation for evaluation about surface facilities and surface local environment, and establishing methodology for uncertainty treatment of geological formation.
Coal is generally used as solid fuel on the surface after open cut mining or underground mining. However, the coal seam mined economically is limited by the geological and technological conditions. In situ method is a promising method, which enables the energy recovery from deep coal seam and under sea coal seam, usually being not economical by conventional mining methods. In "in situ" method the coal is usually converted to gaseous form underground (UCG: Underground Coal Gasification). One of the features of this method is the CO2 storage in coal seam in parallel to the gas production. There are two methods for UCG, combustion and non-combustion methods. The former is the conventional UCG realizing the coal gasification by supplying heat through the combustion of coal seam. The other one is non-combustion method using microbial decomposition and supercritical CO2 extraction for gas production at temperatures of some 10 or 100 degrees Celsius. The CO2-reducer methanogenic archaea are found in underground coal seams, in petroleum reservoirs and in saline aquifers in Japan. The underground bioreactors for CO2-reduction and methanogenesis may be realized in deep coal measures or in underground hydrocarbon accumulations. The former UCG is now booming up for the technology development in the world now towards commercialization. The latter UCG is the still in the R&D stage. This report summarizes the present state of arts of these two UCG methods pressing the gas production and CO2 storage in coal seam.
CO2 sorption on coal was estimated by two experiments, one is heat of sorption measurement and the other is 1H-NMR measurement. In the heat of sorption measurement, differential heat of sorption (qd) was compared with the calculated one. Measured qd was same value with calculated one at low pressure. It decreased gradually with pressure and became lower than the calculated one. Since it couldn't be explained by the theory based on physisorption, it is estimated that the coal-CO2 system could not be explained by only simple physisorption. In 1H-NMR measurement, spin-spin relaxation time (T2) and composition fractions of L1, L2 and G were measured. Composition fractions and T2 of L1 increased with CO2 gas pressure. Furthermore, the correlation was observed between volume increments and dissolution amount at over 10 atm. It indicates that part of CO2 sorption capacity was used to coal relaxation.
A micro pilot test of CO2-enhanced coal bed methane (CO2-ECBM), which is a carbon capture storage (CCS) technique for global warming prevention, was carried out in Yubari. CO2 was injected into a coal seam, which consisted of a cleat and a coal matrix, and the injection rate of CO2 was decreased with time. The matrix swelled as CO2 was adsorbed. Depending upon the constraint conditions, the cleat closed with CO2 injection, and the permeability decreased. In this study, the strain and stress constraint conditions were created in-laboratory and N2 and supercritical CO2 were injected repeatedly in a coal specimen for observation of the permeability, Vp, circumferential strain and confining pressure. In order to achieve the strain constraint condition, a circumferential extensometer was installed in a cylindrical specimen and the output was used to servo-control the confining pressure intensifier. In order for the matrix to adsorb CO2 and swell, supercritical CO2 was injected into the coal seam under the strain constraint conditions, the cleat (passage of flow) was closed, and infiltration of supercritical CO2 was restrained for a short time, and flow was then suspended. A swelling pressure of approximately 6 MPa was observed at this time with adsorption of supercritical CO2 onto coal. When N2 was re-injected into the coal specimen in which supercritical CO2 was injected under the strain constraint conditions, no immediate flow was generated. However, several hours later, when permeation began, the flow was progressively increased. Although the matrix might have adsorbed CO2 and swelled when supercritical CO2 was re-injected into the coal under stress constraint conditions, the cleat was not closed; therefore, infiltration of supercritical CO2 was continued and the flow was not stopped. A swelling strain of approximately 0.6% with adsorption of supercritical CO2 on coal was observed at this time.
Japan CCS Co., Ltd. was incorporated on 26th May 2008 by investment of total 29 Japanese major private companies for the purpose of conducting a total investigation for CCS demonstrations, and early extensive dissemination of CCS in Japan. In the spring of 2009, the company increased its capital and allocated new shares to new shareholders. The total number of shareholders became 37 companies as of 31st July 2009. The company is conducting two projects in the fiscal year 2009; one is the Demonstration Project of the CO2 Abatement Technology, which was assigned by the Ministry of Economy, Trade and Industry, and the other is a part of the Feasibility Study on a Total System from Electric Power Generation to CO2 Storage, which was assigned by the New Energy and Industrial Technology Development Organization. As a part of the former project, the company is carrying out 3D seismic survey for a site characterization and an offshore pipeline route survey over two candidate sites for a CCS demonstration project in Japan. Several monitoring methods are also considered for the CCS demonstration project. 3D and 2D seismic survey and VSP are considered for monitoring of injected CO2 distribution in the reservoir, chemical and physical marine surveys for seepage detection, and seismicity monitoring for assessing any impact to the surface and subsurface facilities of the CCS demonstration. The Japanese Government together with Japan CCS Co., Ltd. and private sectors is advancing toward CCS demonstrations.