Seismic velocity tomography for CO2 monitor in subsurface geological structures

The storage of CO2 in depleted hydrocarbon reservoirs and saline water aquifers is a leading solution to Global Warming due to CO2 emission to the atmosphere. The capture of CO2 from major CO2-emitting plants and its storage in underground geological structures has a potential to reduce Global Warming by about 60%. A procedure for monitoring safe and secure storage of CO2 in underground geological structures is demonstrated in this study using seismic velocity tomography. The tomographic method uses first arrival traveltime to estimate velocity of geological structure along the ray path. The inversion procedure utilizes optimized objective function that consists of two parts: (i) a part that minimizes the misfit between the observed and inverted data, and (ii) a part that enforces the true shape and structure of the real geology. First, the method is applied to invert the velocity structure of a west Texas oilfield, and later to reconstruct the velocity structure of Marmousi models before and after CO2 injection. The results of the tests confirm the appropriateness of the procedure for CO2 monitoring. The inverted velocity tomogram for the post-injection stage shows velocity perturbation due to CO2 presence and the progression in CO2 front. Technology for monitoring CO2 in geological storages as demonstrated in this study is crucial to forestall CO2 leakages and its negative consequences on the environment.