Gaussian beam migration for free-surface multiples in VSP

Abstract

The VSP Gaussian beam migration(GBM) is a kind of both computational efficiency and imaging precision of seismic imaging method ， it can get high-resolution structural features near the borehole. However, the VSP migration based on primary reflection imaging is limited by the observation system, which makes the shallow structure at far offset unable to be imaged. The free-surface multiples in VSP can expand the illumination range at far offset effectively. In this paper, a Gaussian beam migration method for free-surface multiples imaging in VSP is proposed. Firstly, based on the ground Gaussian beam pre-stack depth migration, the method of decomposing the plane wave is improved and adapted into VSP geometry. The paper decomposes the seismic records received by well into plane waves in different direction according to different window center, and images each direction of the plane wave independently. Secondly, the free-surface multiples are converted to primary reflection and imaged by VSP GBM in primary reflection through mirroring the velocity model and receiver point coordinates. Finally, the effectiveness and stability of the proposed method are verified by the typical model and practical data.