Effects of Near‐Surface Absorption on Reflection Characteristics of Continental Interbedded Strata: the Dagang Oilfield as an Example

Abstract:Due to the effects of seismic wave field interference, the reflection events generated from interbedded and superposed sand and shale strata no longer have an explicit corresponding relationship with the geological interface. The absorption of the near‐surface layer decreases the resolution of the seismic wavelet, intensifies the interference of seismic reflections from different sand bodies, and makes seismic data interpretation of thin interbedded strata more complex and difficult. In order to concretely investigate and analyze the effects of the near‐surface absorption on seismic reflection characteristics of interbedded strata, and to make clear the ability of current technologies to compensate the near‐surface absorption, a geological model of continental interbedded strata with near‐surface absorption was designed, and the prestack seismic wave field was numerically simulated with wave equations. Then, the simulated wave field was processed by the prestack time migration, the effects of near‐surface absorption on prestack and poststack reflection characteristics were analyzed, and the near‐surface absorption was compensated for by inverse Q‐filtering. The model test shows that: (1) the reliability of prediction and delineation of a continental reservoir with AVO inversion is degraded due to the lateral variation of the near‐surface structure; (2) the corresponding relationships between seismic reflection events and geological interfaces are further weakened as a result of near‐surface absorption; and (3) the current technology of absorption compensation probably results in false geological structure and anomaly. Based on the model experiment, the real seismic data of the Dagang Oil Field were analyzed and processed. The seismic reflection characteristics of continental interbedded strata were improved, and the reliability of geological interpretation from seismic data was enhanced.