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JOINT IMAGING OF THE MEDIA USING DIFFERENT TYPES OF WAVES A.V. Reshetnikov* Yu.A. Stepchenkov* A.A. Tabakov** V.L. Eliseev** * SPbSU, St-Petersburg, ** GEOVERS Ltd, Moscow

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Introduction Depending on boundaries configuration, different parts of interfaces can be exposed by one or more type of waves. Obviously, all types of waves contain information about properties of the media. It means that in process of imaging of the media all available information should be used. It is also necessary for the derived solution to particularly include one-wave exposure case. Area and boundaries, exposed by waves of different types Upgoing PP wave Upgoing PS wave Downgoing PP wave

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Description of DDR Technology (Dynamic Decomposition of the wave-field and Reconstruction of the media) Set initial velocity model Correct velocity model using first break data Select a boundary Calculate parameters of waves, reflected/refracted on the boundary Selection and subtraction of reflected/refracted waves Imaging of the media using different types of waves Control of mismatch between model and image Correction of the velocity model Exit If all boundaries are correct Results: 1) Velocity model 2) Selected waves of all types 3) Images of the media represented by all types of waves

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Wave-field and wave parameters Model, ray paths and image DDR interface concept

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The way to calculate joint image is summing of the images from all types of waves. It is important to remember that all images dynamically correspond to different physical measures. Therefore images must be normalized before stacking. Resulting measure can be selected as value of P-waves reflection coefficient along normal to the boundary. Then normalization coefficient can be evaluated as Joint imaging where K – reflection coefficient, calculated using reference model; – normalized measure; N – number of summed images. Thus, for all boundaries of the model joint images can be calculated using all types of waves. These images can be composed into one seismic section. In this section amplitudes correspond to the reflection characteristic of the media.

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where - amplitude of downgoing wave - reflection angles of monotype and converted wave, - refraction angles of monotype and converted wave, Calculation of reflection/refraction coefficients for different types of waves To calculate reflection/refraction coefficients in the boundary point the following system is used: - reflection coefficients - refraction coefficients - P and S waves velocities - densities

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Function of reflection/refraction coefficients vs. incidence angle Upgoing PP wave Upgoing PS wave Downgoing PP wave Coefficient value Incidence angle

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Images for different type of waves Reflected PP waveReflected PS wave Refracted PS waveRefracted PP wave

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Joint image of the boundary

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Joint image of the several boundaries

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Conclusion This method allows constructing of full seismic image which represents the media as values of true reflection coefficient along normal to the boundaries. DDR technology provide a practical possibility to build joint image of the complicated media by all available types of waves.

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