Evaluation and Monitoring of CO2 Storage: Utilizing Mathematical Models to Analyze Well Log Data in Response to Incremental CO2 Saturation

Sequestration and Injection of carbon dioxide (CO2) in a geological formation will cause changes in rock seismic velocities. The goal of geological CO2sequestration is to store large quantities of CO2within the underground rock formation. It will be required to know with a high level of confidence that the sequestered CO2remains permanently within the formation. Seismic monitoring could play an important role and ensure safe, effective storage of CO2. This work attempts to model the response of well log data to increasing CO2 saturation, with the objectivesofperforming fluid substitution in the reservoir from brine to CO2 in incremental saturations, and generation ofregression models to relate CO2 saturation to density and sonic log changes. This is achievedthrough Gassmann fluid substitution and regression analysis using well log data from the Norwegian North Sea. Multiple linear regression was generated for both density and sonic velocity to establish a relationship between a constant C, which represents the percentage of the elastic parameter (Vp, Vs or RHO) relative to its original value, and CO2 saturation, shale volume and porosity.The general trend, as expected, is an increase in CO2saturation resulting in increased Vs and decreased Vpand density. The regression models generated from the multiple linear regression can be used to predict the change in VS as well as density (RHO) which can be used to determine the Vs and density changes resulting from changing CO2 saturation. This work serves as a precursor to saturation inversion from time-lapse seismic monitoring of CO2 stored in the subsurface.