Finite difference feasibility modelling of time-lapse seismic noise interferometry for CO2 monitoring

Seismic Interferometry (SI) with ambient noise is a recently developed method for subsurface imaging that involves cross-correlating ambient noise from passive seismic data to reveal the earth’s reflection response. Based on this technique, TNO aims at developing a methodology for efficient monitoring of CO2 geological sequestration in Carbon Capture and Storage projects. In 2009, as a collaboration with the CO2SINK research project on CO2 sequestration taking place in Ketzin, Germany, TNO installed a permanent seismic array that has now already been recording passive data for 2 years during the CO2-injection. The correlation of the large real datasets requires a prior assessment on the feasibility of SI with ambient noise for time-lapse monitoring of the C02 storage process. Using a 1D layered acoustic velocity model of the Ketzin storage site as well as the layout of the TNO’s permanent array, we perform passive experiments that involve finite-difference modelling of passive wavefields from random noise sources and the cross-correlation of these passive synthetic data to retrieve reflection responses. By repeating the experiment for base and monitor velocity scenarios from CO2 saturation changes in the reservoir, we study the influence of various noise parameters (the number of sources, the sources’ duration, the spatial distribution) on the retrieved base and monitor reflection responses as well as their induced amplitude differences. We show that, for a sufficient number of sources with sufficient durations, the accuracy of the retrieved reflection responses from the CO2 reservoir are close enough to the reference responses from an active surface shot. More generally, the retrieved reflections are improved when more sources lie at or close to stationary points. In addition, when the sources characteristics are identical for both the base and the monitor passive experiments, the amplitude differences between the retrieved base and monitor reflection responses exhibit clear information on reflection changes from the reservoir. However we show that, when the sources’ characteristics, such as their spatial random distribution only, are not close enough for the base and the monitor passive experiments, the induced amplitude differences are difficult to interpret. Processing of the recorded body-wave noise prior to cross-correlation might be then necessary. We conclude that the repeatability of the passive noise is crucial for time-lapse interpretation. Finally, we choose an ideal noise configuration to enhance repeatability of the passive experiments when using different random distributions of the sources. In this special case, plotting picked amplitudes from the retrieved reflection responses for different velocity scenarios illustrates the potential of monitoring the velocity changes from SI with ambient noise.

Subject

seismic
interferometry
monitoring
gas sequestration

To reference this document use:

http://resolver.tudelft.nl/uuid:f77e5e5f-2b08-47f0-b825-0637897154d6

Part of collection

Student theses

Document type

master thesis

Rights

Files

PDF

Thesis.pdf.pdf

9.59 MB

Close viewer