Method for seismic processing in particular for compensating for birefringence on seismic traces

摘要

Seismic traces are collected corresponding to two perpendicular components of a wave emitted and reflected underground. For several birefringence hypotheses, at least part of the traces are subject to a series of transformations inverse to the transformations supposed to be encountered by the wave. The best matching hypothesis is selected to give resulting compensated traces : The method involves (a) collecting seismic traces at a point on the surface or in the formation corresponding to two perpendicular components of a cutting wave emitted underground and reflected by different interfaces therein; (b) applying to at least one time period of the traces a succession of transformations which are inverse to the transformations supposed to be those encountered by the wave as it passes through a series of underground layers, with this operation repeated for different hypotheses of birefringence in the different layers; (c) for each hypothesis, the value of a parameter representative of the coherence/similarity of the two resulting traces is obtained, and (d) the hypothesis considered the most representative is selected as a function of these values, the two resulting traces being compensated for underground birefringeance. A hypothesis on the birefringence of a layer is characterised by at least one parameter relative to the orientation of the birefringence axes and at least one retarding parameter introduced into the layer between a propaation along the rapid axis and a propagation along the slower axis. These results are represented in 2D or 3D with for different parts of the trace successions of values corresponding to the values of these parameters for a succession of layers crossed by the wave for the selected birefringence hypothesis. Successive iterations of the process require a new selection of a hypothesis at each iteration, checking to see if the correlation has improved compared to the previous iteration. The period of trace examined is several hundred milliseconds or longer, or samples of 2 to 4 milliseconds.