Method for estimating elastic parameters by inverting 4D seismic measurements

摘要

According to the invention, elastic parameters, including density, pressure wave propagation speed, and/or shear in pervious layers located in a dense underground area along an array of horizontal positions, are estimated by inverting 4D seismic data. Firstly, an estimate of variations in the elastic parameters in one or more starting positions of the array, which can be located on bored wells within the area in question, is obtained. Then, a propagation algorithm is used in order to gradually carry out the 4D data inversion on the basis of the starting positions. The inversion takes into account the previously estimated parameter variations. A spatial variation in the depth and/or the thickness of the pervious lavers in question can also be taken into account. Propagation is based on positions that are consecutively selected as providing optimal values for a cost function assessed in order to invert the 4D data.

主权项

1. A method for estimating elastic parameters of a region of the subsoil meshed according to an array of horizontal positions, the method comprising:
(a) obtaining seismic traces associated with said horizontal positions; (b) obtaining an estimation of variations of elastic parameters in layers of the subsoil in at least one starting position of the array; (c) determining a boundary consisting of the positions of the array which are adjacent to a starting position; (d) obtaining, at each position of the boundary, estimations of variations of the elastic parameters in the layers by minimizing a cost function derived from a seismic wave propagation model accounting for the seismic traces associated with said position of the boundary, the minimization taking into account the estimations obtained at a starting position adjacent to said position of the boundary, and marking each position of the boundary as having been processed; (e) selecting at least one propagation position in the boundary, where the minimized cost function has, within the boundary, a minimal value, then removing the selected propagation position from the boundary; (f) adding to the boundary each position of the network not marked as processed and adjacent to a propagation position selected in the preceding step (e); (g) obtaining, at each position added to the boundary in the preceding step (f), estimations of variations of the elastic parameters in the layers by minimizing the cost function derived from the seismic wave propagation model accounting for the seismic traces associated with said position added to the boundary, the minimization taking into account the estimations obtained at the selected propagation position, and marking each position added to the boundary in the preceding step (f) as having been processed; (h) repeating from step (e).