含泥率の三次元モデル構築:長岡CO_2 圧入実証試験サイトヘの適用

摘要

Abstract We present the depositional environments and geostatistical modeling of the spatial distribution of mud content within a sequence stratigraphic framework for a CO_2 reservoir at Nagaoka, Japan. Carbon dioxide was injected into strata interpreted as deltaic or coastal plain deposits characterized by upward-shallowing successions. The spatial distribution of the mud content, as estimated by geostatistical modeling, shows sandy sediments prograding from the lower to the upper part of the reservoir. Geophysical monitoring during and after CO_2 injection suggests that CO_2 migration within reservoir rocks is inhomogeneous; CO_2 breakthroùghs were observed at two observation wells, but were not observed at one observation well (OB-3), although the wells are located at similar distances from the injection well. The results of geostatistical modeling also indicate the heterogeneous distribution of muddy sediments. The heterogeneity of the CO_2 distribution can be explained by the distribution of muddy sediments around well OB-3, which is located at the most distal (offshore) location. Genetic interpretations of the spatial distribution of mud can be useful for predicting and estimating the distribution of injected CO_2 in a reservoir.