著者

竹原 孝 及川 寧己 藤井 孝志 宮崎 晋行

出版者

一般社団法人 資源・素材学会

雑誌

Journal of MMIJ (ISSN:18816118)

巻号頁・発行日

vol.136, no.11, pp.134-139, 2020-11-30 (Released:2020-11-28)

参考文献数

28

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A project of CO2 injection in the Ishikari coal basin (Yubari-shi, Hokkaido, Japan) since 2002 has shown that injection of CO2 into coal seams affected their permeability. Adsorption of CO2 caused swelling of the coal matrix and lowered the permeability of coal seams, probably because of closure of cleats and pores in the coal seams. However, a temporary recovery of permeability was observed after subsequent injection of N2, suggesting that some amount of adsorbed CO2 was replaced by N2 and the closure of cleats and pores were mitigated. However, the changes of mechanical properties of coal in the process are not yet fully understood. In this study, we injected CO2 and N2 into coal specimens recovered from the Ishikari coal basin and observed the changes of coal strength under hydrostatic pressure and temperatures typical of a coal basin. We conducted triaxial compressive strength tests on the coal specimens to clarify the effects of CO2 and N2 on the mechanical properties. Our results are summarized below.1) We verified that swelling and shrinkage of the coal were associated with adsorption and desorption, respectively, of CO2.2) The triaxial compressive strength tests showed that injection of CO2 caused decreases of peak strength and Young's modulus.3) Both coal strength and Young's modulus recovered when previously injected CO2 was replaced by N2.

著者

及川 寧己 竹原 孝 雷 興林 深沢 洋規 山口 勉

出版者

一般社団法人 資源・素材学会

雑誌

Journal of MMIJ (ISSN:18816118)

巻号頁・発行日

vol.136, no.10, pp.110-116, 2020-10-31 (Released:2020-10-27)

参考文献数

17

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Elucidating the sealing capacity of caprock is very important because CO2 sequestered in deep aquifers can remain there for several hundred years in the CO2 sequestration. Threshold capillary pressure is a key property affecting sealing capacity, and therefore, the ability to measure the threshold pressure of a target rock conveniently is highly sought after. In this study, data collected during the CO2 injection process in triaxial compression tests of mudstone supposed to be a caprock were used to measure threshold pressure via the dynamic method. These triaxial tests were conducted to study the mechanical properties of mudstone below depths of 1000 m. The threshold pressure for 23 out of 26 test samples was successfully measured. Measured values ranged from 0.54 to 1.57 MPa, which was within a reasonable range compared to the results reported by three other studies that used similar mudstone specimens. A small amount of shrinkage induced by a pore pressure decrease, which was caused by a threshold pressure, was observed in the experiment. The threshold pressure showed a positive correlation with the shrinkage, implying that this pressure might be estimated from the shrinkage. Thus, a volumetric elastic constant was calculated from the shrinkage assuming that the decrease in mean pore pressure was half of the threshold pressure. The mean volumetric elastic constant was 0.92 GPa, which was about 40% lower than that of the rocks from which the test samples were obtained. These results indicate that the shrinkage value cannot be directly used to estimate the threshold pressure, and that a correction of this shrinkage value is necessary.

著者

及川 寧己 当舎 利行

出版者

THE GEOTHERMAL RESEARCH SOCIETY OF JAPAN

雑誌

日本地熱学会誌 (ISSN:03886735)

巻号頁・発行日

vol.23, no.4, pp.275-282, 2001-10-25 (Released:2009-08-07)

参考文献数

12

被引用文献数

1