The Research Of Seismic Beam Migration Limited By Dynamic Parameters

In the exploration and development of oil and gas source,seismic data always plays a significant role.The high-quality seismic profile not only can be used for the interpretation of geological layers and faults,but also can provide certain meaningful guidance for the subsequent reservoir simulation and the design of oil and gas wells network.Digital processing for seismic data is a bridge between the acquired field data and the final interpretation results,and the revolution of its theory and techniques marks the overall progress and development of seismic exploration industry.One of the critical technologies,migration processing,is to map common-shot or common-offset data to imaging domain according to seismic propagation law,which is after the processing of denoising,deconvolution,data regularization and other modues.This can help restore the spatial shapes and patterns of geological structures,which reflect the geometric information.Accordingly,true-amplitude migration could illustrate the physical features of subsurface layers.Recently,the commonly used imaging method in practical production is still Kirchhoff migration,which mainly depends on its unparalleled computing efficiencyits great progress of adaptibility.But because of the deficiency of asymptotic ray theory,Kirchhoff migration cannot image the caustic zone and the multiple arrivals.Based on the complex paraxial ray theory,Gaussian beam migration occurs at the right moment,which not only retains the high efficiency and flexibility of ray-based methods,but also can define the complex fault blocks and high steep structures and has a comparative imaging accuracy to wave equation migration.But its initial beam width has too much infulence on Gaussian beam imaging quality.When the initial beam width is too small,the near surface zone has good imaging quality but the imaging result at deep parts is poor because the beam width increases rapidly along with the ray.On the contrary,when the beam width is too big,even though the beam width increases slowly,the big beam width makes the wave field far from the central ray have a low accuracy and then affects the entire imaging quality negatively.Aiming at this problem,from the basic Ray theory and Gaussian beam theory,we use the dynamic parameters to limit the wave field energy and then propose a corresponding seismic beam migration method which could be applicable to complex geological conditions.Using the idea of dynamic parameters,we developed a Fresnel beam migration method for complex topographic conditions and an adaptive focused beam migration method for complex structures areas in this dissertation.The research content mainly includes the following aspects:(1)beginning from the zero-order Ray theory,we derived the kinematic and dynamic ray tracing equations of paraxial ray theory,and then used its complex form to construct Gaussian beam and discussed the features of its beam width,wave front curve and central ray amplitude;(2)we introduced the theory of wave approximation in effective vicinity proposed by Cerveny into topographical migration and then derived the amplitude correction and quadratic travel-time correction,which is helpful to improve the imaging quality of near-surface zones;(3)using the first Fresnel zone to limit the effective energy distribution area of seismic beam,we obtain the Fresnel beam and apply it to the depth migration from irregular topography,which further improve the imaging quality of near-surface results;(4)according to the idea of multiple focusing,we constrained the effective energy of seismic beams within the range of wave-length and then developed an adaptive focused beam migration method,which could improve the imaging quality in strong velocity variation areas;(5)introducing the imaging conditions of elastic RTM into seismic beam migration,we developed the corresponding elastic Guassian beam,elastic Fresnel beam migration and elastic adaptive focused beam migration methods for multiwave and multicomponent data,and its validity has been tested with several classic numerical examples.