Contributions of Rock Physics to Carbon Dioxide Capture and Sequestration

In the CCS project, the monitoring of distributed underground CO₂ is required during the CO₂ injection in order to alarm the CO₂ leakage. Many quantitative monitoring techniques have been investigated and applied at various CCS projects, however, the seismic methods, e.g., seismic reflection, seismic tomography, and sonic logging, are believed as the most promising technique. By using seismic methods, it is desired that the CO₂ salutation values at geological strata are estimated. For this purpose, precise understanding of the relationship between seismic velocity and CO₂ saturation in the rock pore is required. In this review manuscript, three models of rock physics such as the uniform saturation model, the patchy saturation model, and the critical patchy saturation model will be studied by using the time-lapse well logging data obtained at the site of CCS pilot project of Nagaoka, Japan. From our study, the best fitted model to the sonic logging data is the critical patchy saturation model. Additionally, we discuss the size of CO₂ patch in the pore space in relation to the applied seismic wavelength to validate this model.