2.5D Seismic Wave Numerical Simulation And Reverse Time Migration Imaging Based On Curved Mesh Finite Difference Method

Numerical simulation of seismic waves is an important method to study the propagation law of seismic waves and a forward step before obtaining formation imaging.At present,after the continuous innovation and improvement of the seismic wave numerical simulation method,it has gradually changed from solving the 2D numerical simulation problem to the3 D problem.However,in practical application,the amplitude distortion and phase shift problems lead in the calculation accuracy is difficult to meet the actual requirements,while the 3D wave field numerical simulation requires a large amount of computation and computer storage space,which is difficult to be applied to the exploration of large-scale regions.Therefore,in order to solve the problem that the 2D numerical simulation is not accurate enough,the 2.5D wave field numerical simulation method is proposed.The principle is to assume that the physical properties of the geological model remain unchanged along the direction of the direction,and transforms the Fourier transform along the direction,while retaining the source characteristics of the 3D wave field numerical simulation to meet the accuracy requirements.The theoretical premise of numerical simulation of 2.5D seismic wave and inverse time offset imaging is that the model is consistent in the direction of direction,so the Fourier transform can be made along the direction,the 2.5D first-order velocity-stress wave equation expression can be derived,and the finite difference method is used to discrete the wave equation.The conventional rectangular mesh used in the finite difference method causes spurious scattering in a complex model containing undulating interfaces due to the presence of a ladder approximation,Failure to meet the accuracy requirements,Therefore,we used the curved grid finite difference method,Conversion the irregular physical space into the regular computing space according to the principle of straight curved coordinate transformation,To derive the 2.5D first-order velocity-stress equation in the curved coordinate system,And were spatially discretized using a modified DRP / opt Mac Comark difference format,While being integrated in time using the fourth-order Runge-Kutta method,Improve the accuracy of the numerical simulation.The 2.5D seismic wave numerical simulation method is used to calculate the source wave field along the forward and backward direction,respectively,and the 2.5D reverse time offset imaging is performed using the cross-correlation imaging conditions.The conventional offset method is based on the depth domain offset of the single wave,which can not meet the current exploration needs due to the development of recent technology.Therefore,we chose to use the inverse time-shift method based on the wave field push in the time domain,which contains both seismic wave dynamics and kinematic features and is able to make full use of the wave field information,with the significant advantage of not being limited by the formation inclination and offset imaging of multiple waves.The three main processes of inverse time offset imaging are wave field forward performance,inverse time extrapolation,and denoising imaging.