Research On Optimization Method Of Ultra-deep Wide-angle Reflection Observation System Based On Wave Equation

With the development and utilization of oil and gas resources,the focus of oil and gas exploration has continuously shifted to the western regions and sea areas of China,and the target layer of seismic exploration has gradually shifted from medium and shallow to deep.As an important technical means to obtain deep high-quality data,wide-angle seismic exploration has attracted more and more attention.In this paper,by analyzing the main factors affecting wide-angle reflection observation system,the research on the optimal design of wide-angle reflection observation system is carried out.Seismic wave energy are absorbed and attenuated seriously during the transmission process affected by extremely thick loess layer in the Loess Plateau region of Ordos Basin.The collected data is characterized by weak energy,low signal-to-noise ratio,and low resolution.Conventional seismic exploration methods are difficult to explore deep target layers of Meso-Neoproterozoic.However,seismic wave appears characteristic of wide-angle reflection at far offset,which can be used to improve the energy of deep layers and imaging accuracy.And then,a method of optimizing the ultra-deep wide-angle reflection observation system based on the wave equation has been developed.In this paper,firstly,the design criterion of the observation system and the wave equation algorithm are analyzed and studied.And based on various theoretical models,the feasibility of the wave equation algorithm for simulating the appearance of wide-angle reflection is verified.Then based on the seismic and geological conditions of study area,a geological model suitable for the work area is established,combined with the results of theoretical analysis,and forward modeling based on the wave equation is carried out.By analyzing forward results of the single shot records with different offsets,the appearance conditions of wide-angle reflection is found out.On this basis,the spectral characteristics of wide-angle reflection is analyzed,and it is concluded that wide-angle reflection will has a decrease in dominant frequency at the same time as the amplitude energy increases.Meanwhile,the maximum offset of this wide-angle seismic reflection was determined by combining the changing of target layers reflected energy with the offset.Considering the special geological conditions of study area,a safe and efficient low-frequency controllable seismic source is used as the seismic wave excitation equipment.By analyzing acquisition result of different excitation parameters,the parameters of the seismic source were optimized to the best state.Then box wave survey technology is used to statistically analyze the coherent radius of random interference in the study area.Based on the results,comparing the effects of different combinations of geophones,and the best combination of geophones are designed.Then,according to the results of the forward recording and the investigation results of the interference wave,combined with this research and the requirement of production,various parameters of the observation system are determined.Finally,the acquired seismic data are processed,on the basis of forward model results,the conditions and spectral characteristics of the wide-angle reflection can be analyzed.And the data can be stacked.At last,the rationality of the design of this wide-angle reflection observation system is verified with different shots and different channels.