• journal_title：Geophysics
• Contributor：Ranjana Ghosh ; Mrinal K. Sen
• Publisher：Society of Exploration Geophysicists
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.1190/geo2011-0224.1
• journal_abbrev：Geophysics
• issn：0016-8033
• volume：77
• issue：3
• firstpage：M27
• section：Reservoir Geophysics

Finding an appropriate model for time-lapse seismic monitoring of <mml:math><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>CO2-sequestered carbonate reservoir poses a great challenge because carbonate-rocks have varying textures and highly reactive rock-fluid system. We introduced a frequency-dependent model based on Eshelby’s inclusion and differential effective medium (DEM) theory that can account for heterogeneity in microstructure of rocks and squirt flow. We showed that the estimated velocities from the modified DEM theory match well with the laboratory measurements (ultrasonic) of velocities of carbonate rocks saturated with <mml:math><mml:mrow><mml:msub><mml:mrow><mml:mi>CO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>CO2-rich water. The theory predicts significant decrease in saturated P- and S-wave velocities in the seismic frequency band as a consequence of porosity and permeability enhancement by the process of chemical dissolution of carbonates with the saturating fluid. The study also showed the combined effect of chemical reaction and free <mml:math><mml:mrow><mml:msub><mml:mrow><mml:mi>CO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>CO2 saturation on the elastic properties of rock. We observed that the velocity dispersion and attenuation increased from complete gas saturation to water saturation. The proposed model can be used to invert geophysical measurements to detect changes in elastic properties of a carbonate reservoir and interpret the extent of <mml:math><mml:mrow><mml:msub><mml:mrow><mml:mi>CO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>CO2 movement with time. These are the key elements to ensure that sequestration will not damage underground geologic formation and <mml:math><mml:mrow><mml:msub><mml:mrow><mml:mi>CO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>CO2 storage is secure and environmentally acceptable.