Geological constraints in velocity inversion , by Jos van Trier

The result of velocty-inversion methods depends on the parametrization of the velocity model an dthe way it is constrained during the inversion. When a smooth-velocity model is chosen, the velocity inversion can often be performed efficiently, but the risk of finding a non-geological model is severe. In this paper geological information is used to parametrize the velocity model and to constrain the velocity inversion, leading to a more realistic velocity model. An important part of the geological information comes from interpreting the seismic image of the subsurface. The image is obtained by migration-velocity optimization with a smooth velocity model. The smooth, resulting from the optimization, correctly models cumulative traveltimes to reflectors. Structural boundaries are picked from the image, where the boundaries are given a certain width, corresponding to the seismic resolution in the image. The picked boundaries are used to parametrize the velocity model in several structures, each with a velocity function independent of the others. The velocity functions are modeled by splines. A second optimization determines the velocities inside the structures (the boundaries themselves are kept fixed). The data used in the optimization are the traveltimes of rays traveling from reflectors to the surface through the smooth model. The optimization is damped by geological constraints, coming from well logs and general geological information.


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