| The fractured reservoir is an important carbonate reservoir, is becoming the main exploration target of domestic production. Complicated geological situation and heterogeneity, makes the establishment in the geological model of fractured reservoir, seismic identification and prediction of seam is difficult to cave reservoir.Fracture cave can be used as a storage space, and is an important migration channels, so the study of fracture cave has important significance.This paper focuses on the fracture cave reservoir seismic forward modeling and migration problem was studied based on the full acoustic wave equation of high order finite difference wave field continuation operator, fold forward modeling and shifting principle, focal mechanism, the mesh model establishing method, fracture cave seismic characteristic simulation scheme, seam hole model of forward modeling and migration and wave field characteristic analysis of a series of problems.The use of CAD+MISS software to establish a complex model proportion scheme. By CAD software, such as the proportion of rendering model, then output model of high resolution images, by Miss software for image recognition to generate data grid, finally convert grid data in text format is a binary file, and reflection coefficients are calculated using density and speed file. Here the model data preparations are completed.Regular grid, are derived from the full wave equation of high order finite difference divided wave field continuation formula, the wave field continuation operator can adapt to the horizontal to vertical velocity to change, by thunder grams of wavelet with reflection coefficients fold product results as a source to generate specific frequency and bandwidth of seismic wave, and the use of the principle of explosion reflection interface to achieve the time second-order spatial fourth-order finite difference fold after forward modeling and post stack migration. The forward modeling method is more accurate than the convolution method, because the result of this kind of wave equation has not only the exact kinematic feature, but also the dynamic character. And the efficiency of zero offset data section is higher than that of the pre stack forward modeling. At first, the impulse response test is done in the constant velocity medium, and the accuracy of the post stack migration is verified. Then in the aspect to the medium were point diffraction experiment, proved the finite difference stack after forward modeling and migration after stack for the medium transverse velocity adaptation better. After the vertical and horizontal velocity changes in the model of the vertical and horizontal forward modeling after stack migration, but also get the correct results. Finally, through the numerical simulation of the high and steep structural model, get the post stack forward modeling results reflected the characteristics of clear, post-stack depth migration for steep dip realized good imaging, demonstrate the second-order space time fourth order finite difference method can to the complicated structure of wave field propagation accurate simulation.On small scale-post stack forward modeling-resampling-filtering-post stack migration fracture cavity simulation scheme, the comparison between the fracture cave sample post stack forward modeling-post stack migration simulation scheme of scheme and the large scale simulation and analysis results show that the first scheme can well simulate the seismic characteristics of caves and other small scale geologic bodies. In the forward modeling and migration of karst model, found the forward modeling model to smooth the speed of finite difference and post stack migration results were improved significantly. Through the different scales of the separation model of cave and cave on post stack forward modeling and migration, accurately simulate single cave reflection characteristics and multiple cavities produced Beaded reflection characteristics. Of buried hills containing cave model post stack seismic forward modeling, and the different overlying strata velocity of post stack forward modeling results of post stack migration and analysis results in large overlying strata velocity can cause migration arcs, buried hill interface and near buried hill interface insider karst caves and imaging is not clear, difficult to identify the cave; and small in the overlying strata velocity will make inside hill cave space homing incomplete, and the imaging results show the cave size greater than the actual scale, inaccurate results. It is proved that the post stack depth migration for interval velocity accuracy require a higher. The eventual establishment of a West Lungu district complex fracture cave models, model exist karst caves, caves on and fractured zone, using the finite difference stack modeling and stack migration, is to simulate the seismic characteristics of hole slot. Play is from post stack section identification of weathering crust karst cave or cracks with reflection characteristics with great difficulty, and better able to identify these caves or cracks with accurate post stack migration profile. |
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