Crosshole seismic waveform tomography in Changyuan Oilfield, Daqing

Based on waveform tomography, this paper discusses the main steps and strategy of the waveform tomography inversion. As real data are usually band limited due to low frequency missing, a good initial model is needed for waveform tomography, to fill in missed low frequency before the inversion. In the inversion stage, a group of frequencies are used simultaneously in every iteration to suppress noise in the frequency domain. A smoothness constraint on the model in the inversion reduces impacts of noise, non-linearity of the problem, and strong sensitivities of short wavelength model variations. Using waveform tomography in the frequency domain, we reconstruct seismic velocity field between two boreholes with a distance of 230 m. The waveform tomography results provide real and believable geological information that can be tracked between the boreholes although the inversion problem becomes highly non linear due to local geology complexity and rough velocity variations.