| With the development of petroleum exploration and development,exploration demand is changing from simple,large and shallow structure to complex,small and deep structure.In this case,the traditional seismic wave numerical simulation technology has been unable to meet the needs of practical applications.The commonly used finite difference method has the advantages of high simulation accuracy,small amount of computation and easy implementation,but the method can not balance the computational efficiency and accuracy when facing complex media.On the basis of finite difference,variable mesh adopts a more flexible partition form.When facing complex media such as holes,cracks and thin interlayers,small mesh is used in the area requiring fine characterization,and large mesh is used in other areas.This method can not only guarantee the simulation accuracy but also take into account the computational efficiency.Based on the seismic wave propagation theory,this paper deduces the implementation method of conventional grid finite difference in detail,discusses the key problems in the numerical simulation of finite difference,analyzes the main factors affecting the temporal and spatial dispersion,and compares the Clayton boundary with the exact matching layer(PML)boundary.In order to solve the problem that the traditional grid is difficult to balance the simulation accuracy and simulation efficiency,this paper studies the variable grid which can be divided by different grid step size in different regions of the model.By constructing a new partition form to avoid the false reflection caused by interpolation in the transition region,the applicability of PML boundaries to variable grids is studied.Based on the principle of statistics,a random media model with strong heterogeneity is established,and numerical simulation experiments are carried out.The results show that the variable grid is better than the conventional grid in the comprehensive comparison of calculation time and calculation accuracy.Finally,the variable grid is applied to the actual working area model,and the result also shows the superiority of the variable grid. |
