Imaging scatterers in landfills using seismic interferometry

A significant problem with landfills is their aftercare period. A landfill is considered to be safe for the environment only after a relatively long period of time. Until it reaches such a condition, it has to be periodically treated. Not only are treatments very expensive, but they could be dangerous as well; for example, when barriers limiting the waste break. So far, there is no established technique that can predict the leachate and gas-emission potential of a landfill, especially in time-lapse monitoring. This potential depends on the channeling of fluids due to the presence of high-density waste areas and the redistribution of the channels with time. We propose to use seismic interferometry (SI) applied to active reflection seismics to help improve the image of the waste areas (scatterers) and to monitor the subsurface changes in time. Normally, application of SI to reflection recordings from active sources at the surface would result in an erroneous retrieved result, but secondary illumination of the receivers from strongly scattering subsurface, like a landfill, would remedy this problem. We conduct modeling studies to examine the possible benefits of this approach compared to using the conventional seismic reflection method. We show that the reflections retrieved from SI can be used to obtain a clearer image of the shallower scatterers. In addition, we illustrate that time-lapse monitoring using reflections retrieved by SI shows a more repeatable result than the conventional approach in case of source nonrepeatability.