Research Of Migration Based On Dipole Source For Variable-depth Acquisition Data

Conventional marine acquisition uses a streamer towed at a constant depth. The max frequency of marine seismic data is limited by notches. In order to increase the frequency, the cable need to be towed at a shallow depth, but this, in return, compromises the low frequencies. Variable-depth streamer(VDS) acquisition is an acquisition that tows the receivers at variable depths along a cable. Each receiver has a different notch, therefore combing different receivers, the notches will be compensated, and the bandwidth of signals will be broadened. For marine seismic data, there are many source and receiver ghosts generated by the free surface. The ghosts cause angle dependent frequency and amplitude distortion. For better interpretation and inversion, it’s better to correct these ghosts in prestack depth image stage. Depend on this idea, we propose a migration based on dipole source for the purpose of removing the effects of source ghosts and improving imaging precision.Firstly we studied the wave-equation forward modeling for VDS acquisition. During the forward modeling, we solve the problem that most of receivers are not on grids, by interpolating the wave field values of grids around the receiver in each wave field snapshot. And secondly, we learn about the feature of the VDS data, and show the boardband feature of these signals. Then we study the principle of migration and analysis some kinds of common migration method, and mainly learn about reverse time migration(RTM). Using finite difference technique, we achieved RTM, which prepared for the next step of dipole source migration. Thirdly, by means of studying the propagation of wave which comes from one point source, we study dipole sourc e’s wavefield. By the wave-equation forward modeling with dipole source, we get a wavefield which contains source ghosts and then analysis ghost impact on migration. Finally, we achieve dipole source migration by using of dipole source in the method of RTM. Results of modeling and real data processing show dipole sources having a better imaging accuracy than that of conventional RTM.