報告書番号

U98040

タイトル（和文）

堆積岩における圧縮空気貯蔵のための水封機能評価 -- 古第三紀礫岩における孔内水封試験 --

タイトル（英文）

Hydrogeological evaluation for the compressed air energy storage in submerged sedimentary rock -Borehole test for air tightness of Palaeogene congromerate-

概要 （図表や脚注は「報告書全文」に掲載しております）

圧縮空気貯蔵ガスタービン発電システム(CAES)は有望なエネルギー貯蔵技術の一つと考えられる。CAESの貯槽の気密方式としては、地下水による水封方式が経済的に有利であるが、岩盤の水封機能を明らかにすることが必要となる。花崗岩地点では既に孔内試験により水封機能が確認されているが、立地可能性拡大の観点から、堆積岩においても水封機能を明らかにしておく必要がある。今回、礫岩を主体とする古第三紀堆積岩中に掘削した深度600mのボーリング孔を対象に、新たに開発したインナーチャンバー型孔内透気透水試験装置を用い、地下水特性および水封機能に関する調査・試験を実施した。この結果によれは、岩種、岩級によらずいずれの深度においても間隙水圧相当以上の漏気開始圧があることを明らかにし、堆積岩においてもこれまでの花崗岩の場合と同様に水封機能を有することを確認し、水封式CAESの立地可能性を有することを確認できた。

概要 （英文）

In addition to pumped hydro-power stations as large-scaled storage systems, middle sized storage systems are nowadays required for efficient power supply. A system of compressed air energy storage (CAES) with a gas turbine power generator is supposed as an effective way to transfer off-peak electricity in Japan.In order to make the CAES system more economical and more feasible in Japan, a large amount of highly compressed air would be stored in deep excavated caverns without lining. In this case air leakage would be prevented by air tightness of submerged rock. Therefore in order to examine the air tightness of a rock a series of preliminary investigations using boreholes had been carried out in a granitic rock field.From the point of view to expand the feasibility of CAES out of granitic rock fields, similar air tightness of sedimentary rock has been required to be examined. This paper reports the results of geohydrological investigation as well as air tightness test at a sedimentary rock field, where a borehole of 600m depth was drilled and examined.The results are summarized as follows:(1)A test apparatus was newly developed to examine the air tightness of rock in a borehole with rather small diameter of 76mm. The probe of the apparatus has a chamber, which is called an inner chamber and enables to absorb water before injecting air in an isolated section in a borehole.The apparatus can be applied to measure pore pressure as well as to measure small amount of water injected into low permeable rock.(2)According to geohydrological examination water permeability of the rock varies from 6x10^-11m/s to 4x10^-7m/s and distribution of the permeability is supposed to depend not on depth but to group on each unit of repeated sedimentation. Pore pressure is estimated to be nearly static water pressure equivalent to the water level in the borehole. In detail, however, nonuniform distribution was discovered and supposed to be caused by impervious zone in the geological strata.(3)It was discovered that the water pressure transition during pore pressure measurement in an isolated section in the borehole enables to estimate the permeability of rock when we control the speed of inflating pressure of the packers in constant.(4) As a result of the air injection test the submerged sedimentary rock had similar air tightness of granitic rock. Therefore, the CAES system with unlined storage caverns will be applicable to the sedimentary rock and the stored air pressure will be raised at least to the surrounding pore water pressure.

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