Geostatistical modeling for the spatial mud content:

an application to the Nagaoka CO₂ storage site, Japan

Abstract

We present the depositional environments and geostatistical modeling of the spatial distribution of mud content within a sequence stratigraphic framework for a CO₂ 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 CO₂ injection suggests that CO₂ migration within reservoir rocks is inhomogeneous; CO₂ breakthroughs 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 CO₂ 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 CO₂ in a reservoir.