Seismic Wave Modeling And Elastic Reverse Time Migration Method Research Of Heterogeneous Reservoir Based On Dual Variable Grid

The demands of social industrial and development of oil exploration and development technology, makes the oil and gas industry facing more and more complex exploration and development tasks. Oil and gas development of simple structure, large-scale structure and shallow structure can not meet the demands. The exploration center is gradually inclineing to or inclined to complicated heterogeneous reservoirs, which raise higer request to moden oil and gas exploration technology. Conventional seismic forward modeling and migration technology are based on isotropic homogeneous media model, they more or less has some limitations on either theory or application when solving complex heterogeneous reservoir. So it is necessory to seek other methods for researching complex heterogeneous media.The paper considered a variety different scales heterogeneous reservoir (the scale of hetergeous body that larger than seismic wavelength, and smaller than seismic wavelength, and that can compared to seismic wavelength), fractured carbonate reservoir is also included, and carrying out thorough research on seismic forward modeling and migration methods orient to heterogeneous media problems.Discrete of seismic velocity model discrete is the first step of forward modeling, also is an essential step, and it is closely related to computational efficiency and accuracy. In order to facilitate the simulation of inhomogeneous medium, the paper improved velicity model FD mesh generation mode using variable spacing FD grid. Compared to the traditional staggered with fixed spacing, variable grid spacing is discrete heterogeneous geological model more reasonable. Based on variable spacing grid, the paper deduced variable grid discretization formula with arbitrary precision, applied to wave field forward modeling and reverse time migration. Based on variable grid method, the paper developed locally variable timestep scheme to match with variable grid method, which can be called as dual-variable grid method. In a global timestep the fine mesh regions are encrypt calculated by refined with fine time sampling, hence the differenct regions generateed with different grid size can satisfy different stability conditions. The time sampling in wavefield extrapolation can be relax, and improved calculation efficient basicly.Based on dual-variable grid scheme orient to heterogeneous media, the paper applied the thin fluid layer model theory simulated micro-fractured carbonate reservoir. The paper summed up the relationship and knowledge between fracture extension, fracutre density, fracture opening and so on facture characteristic parameters and seismic wave response. And according to the characteristics of fractured carbonate reservoirs, combined with the actual geological conditions of Shengli oilfield, use Fu Tai buried hill reservoir as the main research object, applied the thin fluid layer model to simulate seismic wave propogation of field fracture velocity model.Seismic migration technology as a key technology of reflection seismic plays an important role in seismic exploration. The traditional migration algorithms based on ray tracing theory and one-way wave migration algorithms based on wave equation theory get limitations on solving heterogeneous media, such as Steep glutenite,strong velocity contrast. The paper carried study on elastic reverse time migration based on full wave equation. In order to solve complex vertical micro-fractured media, the paper introduced the dual-variable FD grid into elastic vector reverse time migration extrapolation process, and realized elastic vector reverse time migration of micro-fractured media in carbonate reservoir. This soluted low efficiency and large computational capacity shortcuts of reverse time migration algorithm.