Quantitative interpretation of trapping mechanisms of CO2 at Nagaoka pilot project — A history matching study for 10-year post-injection —

摘要

Demonstrating the permanence of CO2 storage is an important task of pilot projects. In the Nagaoka project, Japan's first pilot-test, a stable containment of CO2 in a reservoir has been successfully demonstrated by kept monitoring the CO2 behavior even after the end of injection during more than 10 years. Systematic and continuous data acquisition of time-lapse well loggings illustrated the detailed nature of CO2 migration at intra-reservoir resolution. In this study, a three-dimensional reservoir model with sub-meter spatial resolution has been developed that involves coupled process of two-phase fluid flow and geochemical transport. The model was history-matched against a set of monitoring data including pressure, well loggings, and fluid samplings over the post-injection period. From the history matching study, the following insights into the trapping processes of CO2 can be drawn: 1) The uneven arrival times of CO2 to the well-depths are well explained by, and consistent with the non-uniform permeability distribution measured at wells;; 2) Slow or even negligible vertical migration of free CO2 inside the reservoir suggests that even a thin intra-reservoir muddy-layer behaves like an impermeable flow barrier to trap CO2;; 3) Pressure-driven-flow during the injection squeezed the formation water out of the reservoir, and subsequent slow diffusive transport of CO2 promoted dissolution of rock minerals including dissolution of calcite and almino-silicates, suggesting precursor of mineral trappingby the precipitation of carbonates such as calcite in the future in this site.