SEISMIC REFLECTIVITY OF A CARBON DIOXIDE FLUX Julián L. Gómez and Claudia L. Ravazzoli CONICET and Departamento de Geofísica Aplicada, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, La Plata, Argentina, jgomez@fcaglp.unlp.edu.ar, http://www.fcaglp.unlp.edu.ar/~jgomez Keywords: Two-phase flow, CO 2 sequestration, Relaxation method, Seismic reflectivity Abstract. In the context of the geological storage of carbon dioxide (CO 2 ), the characterization of the injected CO 2 in a reservoir is of prime importance for volume capacity evaluation and long-term site performance. In this article, we aim to characterize a CO 2 accumulation in a deep layered aquifer by means of its seismic reflectivity. For modeling the vertical distribution of CO 2 saturation in the reservoir, we solve the Buckley-Leverett equation with discontinuous flux function, which describes two- phase flow in porous stratified media. To solve this equation numerically we employ a finite-difference relaxation scheme. The scheme entails an upwinding reconstruction for the spatial derivatives and an implicit-explicit Runge-Kutta scheme for time integrations. Once the vertical distribution of CO 2 is obtained, we use a matrix propagator algorithm to compute in the frequency domain, the generalized reflectivity of the reservoir due to the injected gas. The behavior of this reflectivity controls the amplitude of seismic wave reflections and strongly conditions the detectability of the CO 2 volume in the space-time domain. The numerical approach used in this article is easy to implement and allows to quantify the reflectivity of the carbon dioxide distribution in a practical way. We show that the frequency behavior of the reservoir reflectivity may help to interpret the vertical accumulation of CO 2 , which can be useful as a basis for time-lapse geophysical monitoring. Mecánica Computacional Vol XXXI, págs. 631-649 (artículo completo) Alberto Cardona, Paul H. Kohan, Ricardo D. Quinteros, Mario A. Storti (Eds.) Salta, Argentina, 13-16 Noviembre 2012 Copyright © 2012 Asociación Argentina de Mecánica Computacional http://www.amcaonline.org.ar