The Study of 4D Converted-Wave Seismic Interpretation Methods for CO2 Sequestration

CCUS technology is currently the most effective way to slow greenhouse gas emissions. CO2 geological storage technology is the core of CCUS technology. Combining 4D seismic technology with CCUS (Carbon Capture, Utilization and Storage) technology is the most effective way to confirm security of CO2 sequestration in CO2 geological storage project. However, conventional 4D seismic method mainly study on time-lapse PP reflection information which could not separate fluid saturation and pressure. The potential of using PS wave to monitor CO2-EOR and security of CO2 sequestration has not been explored. Our study focuses on 4D PS-wave. In order to improve our understanding of converted wave in utilization during CO2-EOR and CO2 sequestration. We built two-layer based models in both porous and fracture mediums before and after CO2 injection, and combining with rock physics data and well log data, we got the change rules of elastic parameters of mix fluids changing with injecting pressure before and after CO2 injection. We analyze the changes of PS1 and PS2 AVA curves, and we studied the relationship between time-lapse seismic data with pore pressure and CO2 saturation, then we could confirm the influence of pore pressure and CO2 saturation on 4D multicomponent seismic data. And then, we combined 4D converted wave forward models and 4D PP wave forward models. We studied the effect of pore pressure and fluid saturation on the change of PP-wave reflection coefficients and PS-wave reflection coefficients separately. Combined with the results of fluid substations in different pore pressure and fluid saturation, we could explore the effect of pore pressure and fluid saturation on P-wave velocity, S-wave velocity and density separately. We could establish the relationship between change of PP-wave reflection coefficients and PSwave reflection coefficients and change of pore pressure and fluid saturation. Thus, we computed the change of pore pressure and fluid saturation with 4D PP and PS seismic data.