Fundamental study of the effect of using carbon dioxide in methane hydrate development

1. Fundamental study of the effect of using carbon dioxide in methane hydrate development Kentaro Fukuda Yujing Jiang Yoshihiko Tanahashi Nagasaki University Geoenvironmental Lab

2. Background of Research Methane Hydrate (MH) Now Petroleum and Natural gas are main energy resources. Limit of the quantity of resources Future The development of new energy resources Methane Hydrate (MH)

3. Background of Research MH A material that Methane’s molecule is surrounded in the crystallization of the caged Water’s molecule forms Equilibrium conditions: Low temperature and High pressure Distribution area ① Sediment of sea beds ② Eternal frozen ground area Triangle：Methane’s moleculeBall：Water’s molecule Crystal structure of MH

4. Background of Research Gathered MH(White ice) The gathered MH in Niigata offing Distribution area 1. The Nankai Trough 2. Kuril Islands 3. Sea of Okhotsk 4. Tataru Trough 5. Okushiri submarine ridge 6. West Tsugaru basin The confirmation of existence of MH in sea area around Japan The amount of the resource : About 7.4 trillions cubic meters Equivalent to about 100 years of the amount of annual natural gas consumption in Japan(1999) Possibility of supplying energy for long term in Japan

5. Background of Research MH has the possibility to become the next generation energy However Problem The influence on sea beds in the production of MH (Buckling of winze, Landslide etc.) The necessity of developing MH considering the environment problems

6. Background of Research The suggestion of developing MH with Carbon Dioxide The formation of Carbon Dioxide Hydrate (CO2-Hyd) Advantage • More stable than MH • Disposal of greenhouse gases • Low cost Global environment problem Energy problem Solution at the same time

7. Background of Research CO2 injection CO2 injection Ocean • Maintenance of artificial roof • Immobilization of CO2 Construction of artificial roof Upper layer CO2-Hyd layer CO2-Hyd layer CO2-Hyd layer Production of MH Construction of artificial prop MH layer Stabilization of soft stratum Lower layer

8. Purpose of Research • Evaluate the property by doing triaxial compression test on the specimen with CO2 gas and mixture gas (emphasizing the latter one) Organization of Collaboration：Methane Hydrate lab, National Institute of Advanced industrial Science and Technology • Comparison of the strength on the simulated specimen with each of CO2-Hyd and MH Evaluation of utilization possibility of CO2

9. Sample Manufacture Close-packed Drain Mold of pillar shape (Caliber:50mm, Height:100mm) Water + Toyoura sand Adjustment of the saturation Freeze with refrigerator

10. Sample Set Pressure Container Set of Frozen sample Triaxial Compression Test Apparatus Set of Frozen sample • Installation of Rubber sleeve • Installation of lid of pressure container • Injection of antifreeze solution

11. Formation of CO2-Hyd Establishment of formation conditions Control with outside computers Pore pressure (Formation pressure) : 8MPa Lateral pressure : 9, 10 , 12MPa Temperature in the cell : 6, 2.5 ℃ Penetration of mixture gas in the void of the specimen Adjustment of formation time Formation of CO2-Hyd

12. Triaxial Compression Test Test conditions In situ conditions Undrain conditions Back pressure : 0MPa Pore pressure : 8MPa Lateral pressure : 9, 10, 12MPa Temperature in cell : 6, 2.5℃ Water depth 700m The layer with the thickness of 100m under see beds Establishment of the conditions close to in-situ Enforcement of loading test

13. Decomposition of CO2-Hyd Decomposition of CO2-Hyd by decompression Measurement of the amount of CO2 gases with the gas meter Calculation of CO2-Hyd saturation degree The sample after decomposition

14. Constitution of Sample Gas Gas ガス Vg Vg Pore volume ガス Hydrate Hydrate Vv Vv Water ハイドレート Vh 水 Water Vw 水 Vw CO2-Hyd saturation degree V V Sand Sand Vs 標準砂 標準砂 Vs Core manufacture CO2-Hyd formation

15. Stress-Strain relation (mixture gas) The influence of formation of Hydrate: small Increase of the saturation degree of Sh than that in 6℃ The strength at the same level as N2 Increase of the strength 9MPa

16. Deformation modulus σ σmax σmax/2 ε50 ε E50：Secant elastic modulus in axis difference stress 50 percent σmax：Maximum axis difference stress ε50：Strain in axis difference stress 50 percent

17. Deformation modulus Lateral pressure 9MPa → Linear increase of deformation modulus May depend on the saturation degree of Sh

18. Formation conditions Concentration degree CO2 gas, Methane　→ 100％ Mixture gas　→ The ratio of 50％of CO2 and N2

19. Loading conditions

20. Maximum axis difference stress Linear strength increase Mixture gas: The strength is high. The strength at the same level with MH is shown although their conditions are different.

21. Maximum axis difference stress The possibility that N2 was mixed in the hydrate The strength at the same level with MH despite at low saturation degrees

22. Conclusion Evaluation of the mechanical property of CO2-Hyd Strength Formation pressure Low High Low High CO2 gas Mixture gas Drain conditions Strength MH Mixture gas Drain Undrain Strength at the same level The utilization possibility of CO2 is confirmed

23. Future problem • Applying the triaxial compression test under the conditions more close to in-situ • Elucidation of the change of hydrate saturation degree by the influence of Nitrogen when using the mixture gas Realization of MH development by using CO2

24. END