Carbon sequestration in geological formation is an ongoing effort of the research community to address the issue of curbing excessive anthropogenic CO2 emissions. This dissertation focuses on the development of a theoretical framework in establishing the criteria for geophysical monitoring using passive seismic method. The theoretical framework is established via modeling geological formation using a multi-degree of freedom model. Three main aspects are introduced in this dissertation: 1) the DoReMi passive sensing technique used to monitor CO2 injection at Citronelle Oil Field in Alabama; 2) the multi-physical MDOF lumped mass model employed to simulate wave propagation in an oil field in both linear and nonlinear conditions; and 3) comparisons of the shear wave velocity obtained from the experimental data and numerical simulation results.
Field test results show that shear wave velocity of the strata in the reservoir and the stress changes are consistent. Stress change at oil bearing layer and calcite strata in inverse relationship.
The proposed MDOF model accounts for the influence of stiffness of the geomaterial, which include oil-bearing layer and calcite and saline sand stones. The geological formation of Citronelle Oil Field is used in the numerical simulation. A fourth order Runge-Kutta method is employed for the time integration and a Matlab program was developed for this study. The wave response from the MDOF lumped mass model are changing with the changing properties of CO2 storage layer and overburden layers
(calcite and saline sand layer).
In linear condition, as the stiffness of oil bearing layer changes, spectral amplitude
percentage difference (SAPD) value change is frequency dependent and higher frequency experienced larger changes than lower frequency amplitudes. ???/?? (velocity changes) derived from the simulation results show that the changes varied with depth are detectable. As the stiffness of calcite and saline layer increases, ???/?? has significant changes on the magnitude (as large as 0.35) and similar to the ???/?? obtained from experimental results.
In nonlinear condition, as the stiffness of oil bearing layer changes is controlled by positive or absolute displacement, simulation results show some frequency modes are more sensitive than other frequencies. However, nonlinear phenomenon is not fully understood and need further investigation.
Tripartite spectral plots (TSP) show good visual differences for site condition changes in both linear and nonlinear conditions, but are too complicated to interpret.
The study of the research provided a theoretical understanding of the wave phenomena involved in a typical oil field that is undergoing CO2-EOR process, and the modeling technique can be used to guide the design of geophysical monitoring scheme in the oil field with different geological conditions
