Downhole interferometric illumination diagnosis and balancing

With seismic interferometry or the virtual source method, controlled sources can be redatumed from the Earth’s surface to generate so-called virtual sources at downhole receiver locations. Generally this is done by crosscorrelation of the recorded down-hole data and stacking over source locations. By studying the retrieved data at zero time lag, downhole illumination conditions that determine the virtual source radi- ation pattern can be analyzed without a velocity model. This can be beneficial for survey planning in time-lapse experiments. Moreover, the virtual source radiation pattern can be corrected by multidimensional deconvolution or directional balancing. Such an approach can help to improve virtual source repeatability, posing major advantages for reservoir monitoring. An algorithm is proposed for so-called illumination balancing (being closely related to directional balancing). It can be applied to single-component receiver arrays with limited aperture below a strongly heterogeneous overburden. The algorithm is demonstrated on synthetic 3D elastic data to retrieve time-lapse amplitude attributes