Depositional environments and characteristics of grain size and pore-throat size distributions of CO₂ storage aquifer as a controlling factor of injectivity: a case study of the Nagaoka site, Japan

Abstract

We revealed detailed depositional environments and a controlling factor of CO₂ injectivitiy in terms of grain-size and pore-throat size distributions of the CO₂ storage aquifer of the Nagaoka CO₂ storage site, Japan. The target reservoir rock consists of six sedimentary facies, which is interpreted as prodelta to deltafront deposits. The high injectivity zones correspond to the distributary mouth bar deposits in a deltafront (Facies 3), whereas the low injectivitiy zones correspond to the distributary mouth channel deposits in a deltafront (Facies 2) and prodelta deposits (Facies 5). On the basis of scatter plots of median size versus sorting value of grain-size distributions, Facies 3 is characterized by well-sorted coarser grains. Moreover, pore-throat size distribution of Facies 3 shows larger pore than about 10 phi, indicating a high-permeability networks, whereas those of Facies 2 and 5 show dominant smaller pore-throat sizes. These grain-size and pore-throat features associated with depositional environments appear to be a controlling factor of CO₂ injectivity.