1. China Universty of Petroleum (East China), Qingdao, Shandong 266580, China; 2. Shandong Provincial Key Laboratory of Deep Oil & Gas, Qingdao, Shandong 266580, China; 3. Institute of Geophysics & Geomatics, China University of Geosciences (Wuhan), Wuhan, Hubei 430074, China; 4. Geophysical Research Institute, SINOPEC Shengli Oilfield Company, Dongying, Shandong 257022, China; 5. Research Institute of Exploration and Development, SINOPEC Shengli Oilfield Company, Dongying, Shangdong 257015, China
Abstract：Igneous rocks have significant shielding and absorbing effects on seismic waves and often generate strong reflections,resulting in poor quality of seismic data on the underlying strata below igneous rocks. For the stripping of the strong reflections from igneous rocks,the corresponding time window width can be set according to the interpreted igneous rock horizon information,and the igneous rock horizon can be accurately obtained by searching longitudinal and lateral seismic waveform features to achieve local horizon flattening. Then,the strong reflections from igneous rocks can be stripped by the principal component analysis (PCA) of the sub-volume waveform. On this basis,three-dimensional polynomial surface fitting,instead of Wheeler transform,is performed to achieve local horizon flattening,and a stripping technology of sub-volume waveform PCA based on three-dimensional polynomial surface fitting is developed for strong igneous rock shielding. This method not only avoids the problems of local distortion of the reconstructed seismic signal caused by the failure of the reflection event of igneous rocks to be flattened when using Wheeler transform, but also saves the need to introduce amplitude threshold control into the stripping process. As for the rapid lateral change in the amplitude of the reflection from igneous rocks,the strong reflection from igneous rocks in the sub-volume window can be extracted and stripped laterally by sliding the sub-volume window as long as the amplitude of the reflection from igneous rocks within this window set does not change significantly,which improves the practicability of the method. The model test and application of practical data show that the proposed method allows for high lateral continuity of the strong igneous rock shielding stripped and that it can accurately eliminate the comprehensive response on the interface of the strong reflection from igneous rocks. In this way,it weakens the shielding effect of igneous rocks on the reflected waves from the underlying strata,promotes the ability to identify weak seismic reflections,and ultimately lays a foundation for energy compensation for weak signals and the subsequent processing of those signals.
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