Salt and subsalt structure recovery — An envelope-based waveform inversion with local angle domain illumination compensation and L-BFGS

Abstract

Correct subsalt structure recovery is important for subsalt reservoir exploration. However, high-precision subsalt structure retrieval using full-waveform inversion (FWI) is difficult, which is caused by the shielding from the salt body and the depth of the target. To obtain correct subsalt structures, techniques that can effectively work with deep targets are desired. In addition, the correct recovery of the salt body is critical for the recovery of the subsalt structure. However, the salt body recovery itself is also challenging in FWI, especially when a reasonable starting model is not available. We consider the recovery of the salt structure and subsalt structure. A local angle domain illumination-compensated direct envelope inversion with the local resolution function is developed to provide a large-scale background salt structure with an enhanced and more balanced recovery of the salt body in the deep part. Then, FWI with angle domain illumination compensation is used to improve the recovery of the salt and subsalt structures. To further enhance the quality of the inversion, model updating with the L-BFGS method is embedded into the whole process. Numerical examples with the SEG/EAGE salt model and the Sigsbee model demonstrate that the proposed method could retrieve the salt structure as well as the subsalt structure effectively with high precision starting from a linear initial model.