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＜博士論文＞
炭酸ガス注入下における難透過性岩の水理・力学的特性に関する実験的・数値的研究
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| 概要 | Carbon capture and geological storage (CCGS) has been considered as the most romising option to reduce anthropogenic CO2 emission to the atmosphere, since this technology allows proven fossil fuel res...erves to be used with low emission greenhouse gases. CCGS is defined as a technology of capturing CO2 emitted from major stationary sources such as fossil fuel generated power plants and cement industries, and then compacting to become dense fluid (supercritical) CO2 and transporting it usually via pipeline to a site for being injected into suitable deep rock formation. In the rock formations, CO2 will be confined and by time dissolved to rock formation for long period of times, ranging from hundred years, even in millennia. With mature technology of the enhanced oil recovery (EOR) experienced by petroleum industries since 1970’s, abandoned oil and gas reservoirs are the most readily formation for CO2 storage. However, limited distribution of the reservoirs worldwidely including their lack of collocation with the stationary sources of CO2, which may lead to ineffective cost of CO2 transportation, have prompted deep saline aquifers to become prospective CO2 storage. In case of geological formation in Japan, deep saline aquifers with low permeability sedimentary rocks are expected to become the most readable CO2 geological storage in near future. Yet, study of CO2 behaviour in low permeable rock is needed due to limited data about detail physics governing CO2 flow in sedimentary rocks and inadequate information about geomechanical response of low permeable rock to CO2 injection. Based on these reasons, this study undertook experimental and numerical investigation of hydro-mechanical properties of low permeable rock during injection of CO2. In Chapter 1, the general framework and the background of the problems areexplained, as well as detail plan and brief introduction of the method employed in this study. Literature review is presented in Chapter 2 to illustrate the existing body of knowledge that has been established by previous researchers. It comprises the brief introduction of the CCGS and the constraints encountered in the development of CCGS. Lack of data about CO2-brine multiphase flow systems and geomechanical behaviour of low permeable rock are some of the major problems encountered in the iv design of CO2 geological storage in low permeable rock formation. Therefore, this study sought to fill these gaps, adding to the existing body of knowledge by performing experimental and numerical study on hydro-mechanical properties of low permeable rock during injection of CO2. In this way, newly experimental system of flow pump permeability test was developed in order to measure CO2-water relative permeability and specific storage of low permeable rock and to examine its geomechanical response during injection of CO2. The flow pump permeability test with new experimental system is illustrated in Chapter 3. Ainoura sandstone was used as rock specimen, representing sedimentary rock with low permeability. Initial pore pressure, confining pressure, and temperature applied on the rock specimen were generated to mimic reservoir condition in deep underground. Supercritical CO2 was injected into the rock specimen saturated with water at constant flow rate. The pressures in the upstream and downstream of the rock specimen as well as its longitudinal and lateral strain were continuously measured. In order to interpret experimental results, numerical analysis was developed by modifying the mathematical model of constant flow pump permeability test to deal with two phase drainage displacement flow. It was observed that there are three flow regimes of CO2 flowing through the rock specimen. Relative permeability to CO2 is low, about 0.15 of the relative permeability to water at 100% water saturation. This implies a low efficiency of CO2-water displacement in low permeable rock leading to better CO2 confinement capability of the Ainoura sandstone. The specific storage of low permeable rock increased due to the injection and more pronounced as mechanical rather than hydraulic process. Given by its efficiency and faster determination, flow pump permeability test with new experimental system could provide an alternative approach to measure both relative permeability and storage capacity of low permeable rock injected with CO2 with a more standardized geotechnical laboratory method. The investigation of CO2 solubility effect on CO2 injection into low permeable rock is presented in Chapter 4. Solubility trapping is a potential trapping mechanism which might be taking place for the case of low permeable rock. Therefore, numerical analysis was developed to investigate CO2 solubility based on multiphase and multiv component of mass balance law while Henry’s law was used to quantify the amount of CO2 dissolved into the water. The result suggested that the solubility of CO2 decreases the injection pressure by about -0.821 MPa to -5.45 MPa for CO2 fraction dissolved from 0.002% to 0.005%. In addition, CO2 solubility increases significantly the permeation of CO2 in low permeable rock by 47% to 87%. This indicates the solubility of CO2 could contribute in reducing potential overpressure with more CO2 saturation flowing into low permeable rock formation. In Chapter 5, the investigation of geomechanical response of low permeable rock under injection of CO2 is presented. Numerical analysis based on poroelasticity theory was developed to examine the alteration of stress-strain on the rock specimen induced by the injection. It was observed such a poroelastic expansion of the rock specimen during the injection. The onset of its dilatancy occurred at the condition of the generated pore pressure beyond 60% of the confining pressure applied. Given an increase in the porosity and permeability of the rock specimen, 4% and 2.5 times of their respective initial values respectively, the failure in the rock specimen did not occur. However, their effects on the rock specimen deformations are considerable. As the data of CO2-water relative permeability on the Ainoura sandstone has been obtained in the experimental test as explained in Chapter 3, the data was used in a field scale numerical simulation to investigate the potential ground uplift might be induced by injection of CO2 in low permeable rock (Chapter 6). A field scale model of homogeneous and isotropic Ainoura sandstones formation was created using hydromechanical coupling TOUGH2-FLAC3D with Mohr-Coulomb constitutive model. It was found that the injection of CO2 generated a ground uplift, accounted for average 0.9 cm/year. The peak of the uplift reached about 4.94 cm, 8.5 cm and 21 cm at the period of 5, 10, and 25 years. The results suggested that the injection of CO2 into low permeable rock formation just generates a low ground uplift although its storage capacity is quite small compared to the expected storage capacity for CO2 geological storage in deep saline aquifer.続きを見る |
| 目次 | CERTIFICATE ABSTRACT ACKNOWLEDGEMENTS TABLE OF CONTENTS LIST OF FIGURES LIST OF TABLES NOTATION CHAPTER 1 INTRODUCTION CHAPTER 2 LITERATURE REVIEW CHAPTER 3 NEWLY DEVELOPED FLOW PUMP PERMEABILITY CHAPTER 4 EFFECT OF CO2 SOLUBILITY ON THE INJECTION OF CO2 TO LOW PERMEABLE ROCKS CHAPTER 5 GEOMECHANICAL EFFECT OF THE INJECTION OF CO2 INTO LOW PERMEABLE ROCK CHAPTER 6 GROUND DEFORMATION INDUCED BY INJECTION OF CO2 INTO LOW PERMEABLE ROCK FORMATIONS CHAPTER 7 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS REFERENCES続きを見る |
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| 登録日 | 2013.07.12 |
| 更新日 | 2023.11.21 |