Geophysical Simulation with High-accuracy FDM Multiblock and Hybrid Techniques

Challenges in current geophysical modelling arise from complex structural features of reservoirs including high-velocity deep zones, near-surface phenomena (e.g., karst, low-velocity surface sediments, fractured zones), extreme topography, rapid lateral variations, etc. Previously, we proposed using curvilinear grids in frames of the multiblock technique for an efficient approximation of structural and velocity features of the reservoir by finite-difference discretizations. Recently, we improved the approach in essentially three areas: 1) much more accurate and faster difference schemes inside each block based on the summation-by-parts approach (namely, fourth order accuracy on interfaces instead of the second order and the eighth order inside blocks instead of sixth); 2) a nonmatched grids technique in adjacent blocks for the option of step-type grid refinement/coarsening; 3) the possibility of coupling adjacent blocks discretized by finite differences and by spectral elements method (SEM) schemes, i.e., a hybrid technique of finite difference methods (FDM) and SEM. These features permit us to achieve high accuracy, performance, and flexibility with the novel hybrid multiblock technique by combing advantages of its components – FDM and SEM.