Hitoshi Koide

Subterranean Containment and Long-Term Storage of Carbon Dioxide in Unused Aquifers and in Depleted Natural Gas Reservoirs

Abstract There exist huge volumes of unused aquifers in the earth due to high salinity of the groundwater. Deep aquifers can contain large amount of CO 2 in the form of compressed gas, liquid or aqueous solution under high formation pressure. Natural gas dissolved in saline groundwater is exploited in some areas in Japan. A preliminary technical and economic survey on the CO 2 injection system suggests favorable results. More investigations are necessary for assessment of the effect of CO 2 injection on groundwater environment.

Deep sub-seabed disposal of CO2 — The most protective storage —

The sub-seabed disposal of CO2 is safer than the disposal of CO2 in inland aquifers. Even if small amounts of CO2 seeped out of sea floor, CO2 would disperse and dissolve into sea water. On the surface of the sea, there exist no depressions where CO2 may concentrate. Sediments under deep sea floor are very cool because the deep oceanic water is usually at a few degrees centigrade. CO2 hydrate is formed in sediments under wide areas of ocean floor deeper than about 300m. Virtually complete isolation of huge amounts of CO2 is possible by the deep sub-seabed disposal. Liquid CO2 with heavy suspension intrudes laterally under light unconsolidated sediments at sea floor deeper than about 3700m. Lateral intrusion technique for the super-deep sub-seabed disposal of CO2 can protect the ecology on the sea floor.

Self-trapping mechanisms of carbon dioxide in the aquifer disposal

Abstract Sealing of pores and gaps in sedimentary layers by formation of CO 2 hydrate makes artificial caprocks which can prevent the leakage of carbon dioxide from deeper reservoirs of disposed CO 2 . Perfect isolation of CO 2 is possible in cool sedimentary basins under nearly permafrost conditions and in deep and cool submarine sediments. Complete mitigation of greenhouse gas emission from fossil fuel power plants can be realized by deep subseabed disposal and subterranean disposal of carbon dioxide in cool districts.

Hydrate formation in sediments in the sub-seabed disposal of CO2

Sub-seabed disposal is the safest disposal option for CO2. Water pressure and dilution into oceanic water prevent direct emission of CO2 into the air. Sediments under the deep sea floor are usually cool because the deep oceanic water is very cool. CO2 hydrate forms in the sediments in areas of the sea floor deeper than 300 m. The formation of CO2 hydrate in sediment pores almost completely prevents the escape of CO2.

Underground storage of carbon dioxide in depleted natural gas reservoirs and in useless aquifers

Koide, H., Tazaki, Y., Noguchi, Y., Iijima, M., Ito, K. and Y. Shindo, 1993. Underground storage of carbon dioxide in depleted natural gas reservoirs and in useless aquifers. In: M. Arnould, T. Furuichi and H. Koide (Editors), Management of Hazardous and Radioactive Waste Disposal Sites. Eng. Geol., 34: 175-179. Depleted reservoirs of natural gas and petroleum can provide excellent traps for carbon dioxide. Deep aquifers, which are not used due to high salinity, can host larger amount of carbon dioxide under their high formation pressure than natural gas and oil reservoirs. Small fractions of aquifers in sedimentary basins in the world are enough to host about 87 gigaton-C of carbon dioxide. A preliminary technical and economical survey on the carbon dioxide injection system suggests that the energy requirement for carbon dioxide injection into subterranean aquifers is about 269 kWh/ton-C and that the investment and operation costs for the system are 79

Carbon dioxide injection into useless aquifers and recovery of natural gas dissolved in fossil water

/ton-C. By our preliminary cost estimation in Japan, the CO2-emission-free electricity generation may become possible with a cost increase of 35% for natural-gas-fired power stations, and of 60% for coal-firedpower station,

Geological Disposal of Carbon Dioxide and Radioactive Waste in the Geotectonically Active Country of Japan

Abstract Huge reserves of natural gas in saline aquifers remain still unused in many sedimentary basins in the world. The authors propose an underground injection system of gaseous carbon dioxide into useless saline aquifers in sedimentary basins. The gaseous carbon dioxide is recovered from flue gas of fossil fuel fired power stations possibly by amines. Recovery of natural gas dissolved in the pumped-up saline groundwater can compensate the loss of electric power for the carbon dioxide injection. Our tentative survey suggests that small fractions of useless saline aquifers in sedimentary basins in the world are enough to host about 320 gigaton of carbon dioxide. A preliminary technical and economical survey was conducted on this carbon dioxide injection system for fossil fuel fired power plant. The CO 2 emission-free electric power generation is possible by this underground carbon dioxide injection system with the probable 35% cost increase for LNG fired power plant or 60% increase for coal fired power plant.

Geologic Problems of Radioactive Waste Disposal

In Japan, site selection for geological disposal of radioactive waste (RW) and carbon dioxide (CO2) is very important because of the large regional differences in tectonic activity. Assessment of the long-term stability of geological environments is key to geological RW disposal in Japan. A comprehensive system of long-term prediction of crustal movement and the groundwater regime around the virtual RW disposal sites has been developed in Japan. CO2 is naturally abundant, but geological disposal of the gigantic volumes of CO2 may have big impacts on the environment. One of the adverse effects of underground fluid injection is that it may induce earthquakes. Underground carbon microbubble injection accelerates advanced geological disposal mechanisms. The autogenously sealed ‘CO2 capsules’ can be formed in large basaltic sheets, ophiolite complex and oceanic crust. Sub-seabed aquifers under the deep sea floor can provide very safe and virtually limitless CO2 disposal. Different disposal strategies for CO2 and RW are needed because of the extreme difference in their toxicity and volume. The dispersion and dilution principle is possible for the CO2 disposal, while RW is strictly contained by the multiple barrier system. The stability of the geological environment is important for both CO2 and RW disposal.

Effects of Griffith cracks and inclusions on fracture criteria under a general triaxial stress state.

Japans current research emphasizes the generic validation of geologic disposal and general survey of geologic environment of the Japanese islands. Understanding geologic setting is essential to the assessment of longterm safety of radioactive waste disposal. Scenarios for safety assessment of high level waste disposal should include even natural events of very low probability and very slow geologic processes.Geologic predictions should be based on extrapolation, natural analog, probability, experiments, conceptual model, numerical simulation and safety-assessment model. The geologic environment at the depth of several hundreds and some 1, 000 meters should be clarified to predict the fate of buried radioactive waste. In situ experiments are planned for the examination of validity of long-term isolation system of high level waste.Long-term stability of the geologic environment is of primary importance in disposal of radioactive waste in Japan. The nature and behavior of deep groundwater provide key to the modeling and quantitative evaluation of performance of high-level waste isolation system.

Effect of Confining Pressure and Pore Pressure on Permeability of Inada Granite

New cracks are formed in a rock around Griffith cracks or Griffith inclusions with various aspect ratios and various mechanical characteristics. Parabolic Griffith-type criteria for fracture can be derived from the analysis of the condition for formation of new cracks from the penny-shaped cracks or inclusions. The parabolic criteria for fracture for the incompressible Griffith inclusions become more flattened as they are less sensitive to compressive stress. The closure of Griffith cracks with various aspect ratios leads to the linear Coulomb criteria for brittle fracture.However, the effect of intermediate principal stress is neglected in the conventional theory of generalized Griffith fracture criteria, although it is against the recent results of general triaxial compression experiments of rocks. The statistical distributions of aspect ratio and orientation of Griffith cracks or Griffith inclusions should be considered in order to explain the effect of intermediate principal stress on the fracturing of rocks. The von Mises criteria and Mogi criteria are derived as the special cases of the statistical generalized Griffith theory.