Purpose of I2CNER-CO2 storage division
Carbon Capture and Storage (CCS) is recognized as a reliable mitigation option for substantially reducing CO2 emissions from fossil fuel combustion and from hydrogen-production. Large-scale CCS can have near-term impact on emissions, and can contribute significantly to a carbon-neutral future. The roadblocks for large-scale implementation of CO2 storage are (a) risk of CO2 leakage, (b) risk of induced seismicity, and (c) high-cost. Because these roadblocks are strongly related to the highly uncertain local geological characteristics of potential storage sites, (1) reservoir characterization and (2) monitoring and modeling of injected and leaked CO2 are crucial steps in the development of CCS. The CCS Division of I2CNER addresses these underlying scientific issues, and thus provides tools to enable large-scale development of CCS. In particular, our Division focuses on monitoring and modeling of injected and leaked CO2 in geological structures typical in Japan. For CO2 storage in geological formations typical in Japan, the following issues should be considered.
Heterogeneous geological formation
Because geological formations in Japan are complicated compared to the large-scale CO2 injection sites in other countries (e.g., Australia), we need to consider heterogeneity in constructing geologic models and in designing monitoring surveys. Furthermore, since it is difficult to find structural closure (i.e., anticline structure) for CO2 injection in the Japanese islands and around their continental margins, we need to consider CO2 storage using the mechanisms of residual trapping, dissolution trapping, and mineralogical trapping. Reservoirs without structural closure in the Japanese islands have a capacity of over 100 billion tons CO2.
Limited information for CO2 storage
A limited number of wells provide geological data for the Japanese islands, and there is limited geophysical data available that can be brought to bear for CO2 injection into aquifer formations, although much well data can be used for CCS-EOR (enhanced oil recovery) projects in oil fields. Therefore, modeling and monitoring for Japanese CCS projects will be different from conventional CCS approaches (e.g., CCS in oil fields). Specifically, we need to develop a reservoir characterization method to construct geological models from limited geophysical/geological data.
Since monitoring in CCS projects should extend about several hundred years, the requirements are much different from the conventional approaches in EOR. We need to develop the capability to monitor injected CO2 using simple, convenient methods. For example, we are developing a geophysical monitoring technique using the noise signal of ground termer. Furthermore, the water in many Japanese geological formations has low salinity. Thus, the dissolution rate, as well as chemical reaction rates, of injected CO2 should be considered for long-term modeling.
Earthquakes and CCS
Earthquakes are a critical issue in Japan. Since CO2 injection changes the pore fluid pressure of the reservoir, we must accurately monitor and control pore pressure variations due to CO2 injection near seismogenic faults, and prevent generation of large earthquakes.
New CCS concept suitable for geological formations typical of Japan
We are developing new approaches to CCS, specifically suited for Japanese geological formations. We focus on decentralized, renewable, and deep-offshore CCS. In decentralized-CCS, the major trapping mechanism is driven by dissolution. Because pore pressure is not changed by dissolved CO2 injection, we can safely inject CO2 into a relatively shallow reservoir (~100 meters) at low cost. In renewable CCS, we convert the injected CO2 into CH4, providing fuel for Japan. In deep-offshore CCS, we can inject a large amount of CO2 into deep-sea sub-seafloor reservoirs near Japan (e.g., in the Sea of Japan). For this CCS approach, we need to study the motion and dissolution of CO2 drops as well as hydrate film formation. Furthermore, we need to consider transportation of CO2 to deep-offshore CCS.
Prof. Takeshi Tsuji,“The methods of selecting and characterising a CO2 geological storage site in Japan”,
the 15th Study Meeting held by Global CCS Institute Japan Office, February 26, 2015. (Japanese only)