Improving the virtual source method by wavefield separation
Main Content:
     The virtual source method has recently been proposed to image and moni-
tor below complex and time-varying overburden. The method requires surface
shooting recorded at downhole receivers placed below the distorting or changing
part of the overburden. Redatuming with the measured Green’s function allows
reconstruction of a complete downhole survey as if the sources were also buried
at the receiver locations. Some challenges still need to be addressed in the vir-
tual source method such as limited acquisition aperture and energy reflected
downward from the overburden. 
We demonstrate that up-down wavefield sep-aration can substantially improve the quality of 
virtual source data. First, ii allows us to eliminate artifacts associated with the limited acquisition 
aperture typically used in practice. Second, it allows us to reconstruct a response in the
absence of down-going multiples from the overburden. These improvements are
illustrated on a synthetic dataset of a complex layered model modeled after the
Fahud field in Oman, and on ocean bottom seismic data acquired in the Mars
field in the deepwater Gulf of Mexico.