The overarching goals of the division include: the development of methods of reservoir characterization for pre-injection site selection and post-injection predictions of CO2 fate; realization of new effective monitoring of injected/leaked CO2 to help ensure safe and permanent CO2 sequestration; and proposition and realization of innovative carbon storage concepts suitable for geological formations and rock types typical in Japan (i.e. tectonically active area). To accomplish these goals, we are pursuing fundamental research to elucidate key pore-scale processes that drive effective residual, solubility, and mineral CO2 trapping. We are also developing methods for up-scaling this understanding to inform reservoir-scale predictions.
With respect to reservoir characterization, efforts are directed at understanding rock heterogeneity in constructing geologic models and in designing monitoring surveys owing to the complicated nature of such formations in Japan compared to that in other countries (e.g., Australia). Furthermore, since it is difficult to find structural closure for CO2 injection in the Japanese islands and around their continental margins (i.e., anticline structure), substantial research effort is focused on uncovering the physical mechanisms responsible residual, dissolution, and mineralogical trapping of CO2 in porous formations. The current efforts involve collaborative experimental, modeling and simulation efforts to develop a comprehensive suite of tools that can be utilized in the future for robust prediction of CO2 migration fate in the heterogeneous rock structure typical of Japan. An additional key focus area in this regard is the development of experimental capabilities that provide venues for studying the behavior of CO2 in a range of contexts at pressures and temperatures relevant to actual CCS applications, including liquid CO2 behavior in model and actual rock structures as well as CO2 fate upon leakage into the ocean through compromised cap rock (using a new high-pressure water tunnel to be installed at Kyushu in FY2013). Finally, effort is directed toward developing reservoir characterization methods to construct geological models from limited geophysical/geological data.
With regard to monitoring and modeling of injected and leaked CO2, efforts are directed to the development and deployment of monitoring methods that can address the very long time scales associated with permanent trapping of CO2 in geological formations (which are much different than those utilized in CO2-based enhanced oil recovery, for example). We are therefore developing a geophysical monitoring technique using the noise signal of ground tremors. To address potential leakage from sub-seabed storage sites, we are also developing monitoring techniques using seafloor-based acoustic tomography and pH/pCO2 sensors mounted on an autonomous underwater vehicle (AUV) as well as on a remotely-operated underwater vehicle (ROV). Finally, since the water in many Japanese geological formations has low salinity, the dissolution rate, as well as chemical reaction rates, of injected CO2 are being studied for successful prediction of CO2 dispersion fate should it be leaked into the ocean.
● RESEARCH HIGHLIGHTS
The CCS Division has undertaken a substantial refocusing of its short- and long-term research objectives during FY 2012, with wide-ranging accomplishments focused on the two main research foci of reservoir characterization and monitoring and modeling of injected and leaked CO2.
The second highlight involves development of strategies for detecting and monitoring CO2 leakage from the seafloor, using instrumentation and equipment that we have developed and tested. This development (Shitashima et al., Applied Geochemistry, 30, 14-124, 2012) culminated in a collective approach for detection and monitoring of CO2 leakage in sub-seabed CCS via detection of CO2 leakage using seafloor-based acoustic tomography, followed by mapping the distribution of the leakage points using a novel pH/pCO2 sensor installed on an AUV, and then monitoring of the impacted area using a remotely operated underwater vehicle. This development is ground-breaking as it represents the first published work describing a comprehensive approach for effectively monitoring of CO2 leakage in sub-seabed CCS and represents a critical advance toward another of our CCS objectives, specifically long-term, reliable monitoring of leaked CO2.
The final highlight addresses the fate of CO2 within porous rock structures leveraging the fact that the physical properties of rocks are controlled by the fluid state in the pore space, meaning property variations extracted from geophysical monitoring can be exploited to understand CO2 behavior in the reservoir. In seismic approaches, the change in seismic velocity can be used to evaluate the distribution of injected CO2, since the P-wave velocity decreases dramatically with increasing as CO2 infiltration. To construct these relationships from geophysical monitoring, extensive laboratory experiments have been previously conducted (Kitamura et al., Journal of MMIJ, 128, 511-518, 2012), though these relationships are strongly influenced by pore geometry as well as by pressure and temperature (PT) conditions. Therefore, in order to generate a quantitative description of CO2 migration in porous media and to construct relationships between CO2 saturation and field-derived properties, we developed a digital three-dimensional rock model using a discrete-element method and applied a two-phase Lattice Boltzmann Method (LBM) implementation to compute supercritical CO2 distributions within the pore space (Tsuji et al., Geophysical Research Letters, 39, L09309, 2012; AGU fall meeting, GC51A-1176, San Francisco, December 3-7, 2012). These results were then used to calculate elastic and electrical properties using a finite-element method, as a means of constructing a relationship between CO2 saturation and survey-derived properties (i.e., seismic velocity and electric resistivity). These relationships are crucial for accurate estimation of CO2 behavior from time-lapse geophysical surveys. This on-going work therefore represents a crucial component of our CCS objective to understand and eventually model CO2 fate in geological formations and the viability of pore-space trapping mechanisms, particularly residual trapping.
● FUTURE DIRECTIONS
The CCS Division will continue focusing on its short-term objectives of reservoir characterization and monitoring and modeling of injected and leaked CO2, as developed in collaboration with the EAD, are crucial steps toward the execution of CCS projects in Japan. Of particular focus will be the local heterogeneity when constructing geological models for modeling studies, as well as for the design of geophysical monitoring surveys. In parallel, we will continue our efforts toward understanding and modeling CO2 injection using the mechanisms of residual, dissolution, and mineralogical trapping. We will also accelerate our efforts to develop a reservoir characterization method to construct geological models from the limited geophysical and geological data. A key aspect of overall mitigation is understanding issues of seismicity, so the CCS division will also develop new and novel tools to monitor and control the pore pressure variation due to CO2 injection, in order to prevent generation of large earthquakes due to CCS, with specific focus on geological formations typical of those in Japan.
We have begun, and continue, to develop new CCS concepts suited for geologic characteristics in Japan. We focus on the decentralized, renewable, and deep-offshore CCS. In decentralized CCS, the primary trapping mechanism is dissolved trapping. Thus, we can safely inject CO2 into a relatively shallow reservoir (~100 meters) at low cost. In renewable CCS, we propose to convert injected CO2 into CH4. This CCS approach will provide hydrocarbon fuel for Japan. In deep-offshore CCS, we can inject large amounts of CO2 into deep-sea sub-seafloor reservoirs around the Japanese islands (e.g., Sea of Japan). These CCS approaches will allow us to inject large volumes of CO2 at many sites in and offshore of Japan.
Finally, the CCS Division is committed to applying the techniques we have developed to ongoing CCS projects, and are planning to apply these techniques to future CCS projects that are being planned. For example, the I2CNER-CCS Division is now officially collaborating with the Japan CCS Corporation on the Tomakomai CCS project, where we analyze geophysical and geological data from the Tomakomai CCS project for monitoring purposes.
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