Diagnosing Virtual Source Radiation Characteristics without a Velocity Model

With seismic interferometry, controlled sources can be redatumed from the Earth's surface to downhole receiver locations without a velocity model. As redatuming operators are taken directly from the data very accurate results can be achieved. The redatumed field does not only contain scattered arrivals but also a virtual source function at zero time lag. Under optimal illumination conditions, this virtual source function will be close to a bandlimited delta-function. If such conditions are not present, the virtual-source function will carry an illumination footprint, which can provide useful information on the radiation characteristics of the generated virtual source. By analyzing the contribution of each surface shot to the virtual source illumination footprint individually and selecting subsets of shots based on such analysis, virtual source radiation characteristics can be manipulated. Such manipulation can simplify interpretation and reduce costs of time-lapse virtual source data as monitor surveys can be designed economically to illuminate only particular target areas. We emphasize that all this can be done without the use of a velocity model.