Norio Tenma

Model study of the thermal storage system by FEHM code

The use of low-temperature geothermal resources is important from the viewpoint of global warming. In order to evaluate various underground projects that use low-temperature geothermal resources, we have estimated the parameters of a typical underground system using the two-well model. By changing the parameters of the system, six different heat extraction scenarios have been studied. One of these six scenarios is recommended because of its small energy loss.

Laboratory-Scale Experiments of the Methane Hydrate Dissociation Process in a Porous Media and Numerical Study for the Estimation of Permeability in Methane Hydrate Reservoir

An experimental study of the dissociation of methane hydrate (MH) by hot-water injection and depressurization was carried out at the National Institute of Advanced Industrial Science and Technology (AIST). These experiments helped us understand some important aspects of MH behavior such as how temperature, pressure, and permeability change during dissociation and gas production. In order to understand the experimental results, a model of MH dissociation in a porous media was designed and implemented in a numerical simulator. In the model, we treated the MH phase as a two-component system by representing the pore space occupied by MH as a separate component. Absolute permeability and relative permeability were formulated as a function of MH saturation, porosity, and sand grain diameter and introduced into the numerical model. Using the developed numerical simulator, we attempted history matching of laboratory-scale experiments of the MH dissociation process. It was found that numerical simulator was able to reproduce temperature change, permeability characteristics, and gas production behavior associated with both MH formation and dissociation.

Strengthening mechanism of cemented hydrate‐bearing sand at microscales

On the basis of hypothetical particle-level mechanisms, several constitutive models of hydrate-bearing sediments have been proposed previously for gas production. However, to the best of our knowledge, the microstructural large-strain behaviors of hydrate-bearing sediments have not been reported to date because of the experimental challenges posed by the high-pressure and low-temperature testing conditions. Herein, a novel microtriaxial testing apparatus was developed, and the mechanical large-strain behavior of hydrate-bearing sediments with various hydrate saturation values (Sh = 0%, 39%, and 62%) was analyzed using microfocus X-ray computed tomography. Patchy hydrates were observed in the sediments at Sh = 39%. The obtained stress-strain relationships indicated strengthening with increasing hydrate saturation and a brittle failure mode of the hydrate-bearing sand. Localized deformations were quantified via image processing at the submillimeter and micrometer scale. Shear planes and particle deformation and/or rotation were detected, and the shear band thickness decreased with increasing hydrate saturation.

Triaxial testing system for pressure core analysis using image processing technique

In this study, a newly developed innovative triaxial testing system to investigate strength, deformation behavior, and/or permeability of gas hydrate bearing-sediments in deep sea is described. Transport of the pressure core from the storage chamber to the interior of the sealing sleeve of a triaxial cell without depressurization was achieved. An image processing technique was used to capture the motion and local deformation of a specimen in a transparent acrylic triaxial pressure cell and digital photographs were obtained at each strain level during the compression test. The material strength was successfully measured and the failure mode was evaluated under high confining and pore water pressures.

Coupled LBM–DEM Micro-scale Simulations of Cohesive Particle Erosion Due to Shear Flows

In this paper, the erodibility of cohesive micro-scale particles is investigated for a range of surface shear stresses. Compacted layers of particles, formed by compressing 100 cohesive spheres together, are subjected to shear flow conditions. Fluid–particle interactions are solved using the lattice Boltzmann method (LBM), while the particle–particle interactions are treated by coupling with the distinct element method (DEM). Results reveal a clearly defined critical surface shear stress, beyond which erosion occurs, and a linear relation between the rate of erosion and excess surface shear stress. Further to this, an interesting mechanism by which detached particles gain upward movement is observed. This work also serves to highlight the potential of the coupled LBM–DEM approach for modelling dynamic erosion processes in three dimensions.

Development of Hot Dry Rock Technology at Hijiori Test Site: Program for a Long-Term Circulation Test

Abstract Since 1985, the New Energy and Industrial Technology Development Organization (NEDO) has continued the development of hot dry rock power generation in Hijiori Hot Dry Rock test site, Yamagata prefecture, Japan, as part of the Sunshine Project and succeeding New Sunshine Project sponsored by the Agency of Industrial Science and Technology (AIST), a branch of the Ministry of International Trade and Industry (MITI). The objective of this project is to identify the feasibility of a Hot Dry Rock power generation system in Japan. Thus, the research and development being undertaken at Hijiori HDR test site is aiming to establish hot rock drilling technology, logging borehole technology for evaluating the state of the rock around the well, hydraulic fracturing technology for creating artificial fractures in rock, fracture mapping technology for surveying the reservoir area, and. reservoir evaluation technology for predicting reservoir longevity.

Experimental Study on Improvement of Permeability and Gas Production Behavior by the Simultaneous Injection of Hot Water and Nitrogen-Estimation of Permeability in Methane Hydrate Reservoir, Part3-

Methane hydrate is one of the potential resources of natural gas in the near future, because it exists in marine sediments or in permafrost regions worldwide. Some extraction methods of methane hydrates from the reservoir has been proposed, such as depressurization, thermal stimulation and inhibitor injection. These are all based on the in-situ dissociation process of methane hydrates that is transformed into methane methane and water. Therefore, it is very important to clarify the physical phenomena of gas-water multiphase flow in porous media and the properties of formation and dissociation of methane hydrates.We have carried out the experimental study on hot water injection as one of the thermal stimulation methods. From the results, it was found that (1) when temperature in downstream zone of sand column was lower than equilibrium condition, additional hydrate growth was promoted at downstream zone due to migration of cooled water and dissociated gas, (2) as a result, differential pressure increased exponentially, and water permeability of sand column decreased drastically.For inhibition of hydrate growth and improvement of permeability in hydrate reservoir, we conducted further experimental work on the simultaneous injection process of nitrogen and hot water. Nitrogen has the effect as an inhibitor as well as methanol and salts. In this experiment, firstly, nitrogen was injected into sand column to displace free methane gas, and then hot water injection was started. In the progress of dissociation, temperatures in the sand column and differential pressures, production rate of dissociated gas were measured. Additionally, based on measuring data, water permeability in dissociation process was estimated. Due to the inhibitor effect of nitrogen, it was possible to continue water injection without permeability reduction. Thus dissociated gas production was completed earlier in comparison with normal hot water injection process.