Prestack depth migration using adaptive focused beams

Abstract

Gaussian beam migration is an effective and robust depth imaging method, which overcomes the disadvantage of Kirchhoff migration in imaging multiple arrivals and has no steep-dip limitation of one-way wave equation migration. But its imaging quality depends on the initial beam parameter, which makes the beam width increasing and wave-front spreading with the propagation of the central ray, resulting in poor migration accuracy at depth, especially for exploration areas with complex geological structures. Aiming at this problem, we present an adaptive focused beam method for shot-domain prestack depth migration in this paper. Using the input velocity field information, we firstly derive an adaptive focused beam parameter, which makes a seismic beam focused along the whole ray and improves the wave-field construction accuracy in both the shallow and the deep regions. Then, we introduce this parameter into the Gaussian beam migration, which not only improves imaging quality of deep reflectors but also makes the shallow small-scale geological structures well-defined. Besides, using the amplitude-preserved extrapolation operator and deconvolution imaging condition, the concept of amplitude-preserved imaging has been included in our method. Typical numerical examples and the field data processing result demonstrate the validity and adaptability of our method.