Iterative inversion of data from simultaneous geophysical sources

摘要

Method for reducing the time needed to perform geophysical inversion by using simultaneous encoded sources in the simulation steps of the inversion process. The geophysical survey data are prepared by encoding (3) a group of source gathers (1), using for each gather a different encoding signature selected from a set (2) of non-equivalent encoding signatures. Then, the encoded gathers are summed (4) by summing all traces corresponding to the same receiver from each gather, resulting in a simultaneous encoded gather. (Alternatively, the geophysical data are acquired from simultaneously encoded sources.) The simulation steps needed for inversion are then calculated using a particular assumed velocity (or other physical property) model (5) and simultaneously activated encoded sources using the same encoding scheme used on the measured data. The result is an updated physical properties model (6) that may be further updated (7) by additional iterations.

主权项

1. A computer-implemented method for inversion of measured geophysical data to determine a physical properties model for a subsurface region, comprising:
(a) obtaining the measured geophysical data from a geophysical survey of the subsurface region; (b) inverting the measured geophysical data by iterative inversion process, using a computer, to determine an updated physical properties model for the subsurface region from an initial physical properties model, wherein:
(i) at least one iteration of the iterative inversion process comprises:
simultaneous encoded-source simulation of survey data representing a plurality of survey sources, or receivers if source-receiver reciprocity is used,wherein source or receiver signatures in the simultaneous encoded-source simulation are encoded, resulting in a simulated simultaneous encoded-source or encoded-receiver gather of geophysical data,the iterative inversion process involving updating the initial physical properties model to reduce misfit between the simulated simultaneous encoded-source or encoded-receiver gather anda corresponding simultaneous encoded-source or encoded-receiver gather formed by summing gathers of measured survey data encoded with the same encoding functions used in the simultaneous encoded-source simulation, andthe updating includes determining an update to the initial physical properties model from a gradient of a cost function characterizing the misfit with respect to a parameter that describes the initial physical properties model and perturbing the initial physical properties model in direction of the gradient, and(ii) at least one iteration of the iterative inversion process is performed by sequential source or receiver inversion; (c) downloading the updated physical properties model or saving it to computer storage; and (d) generating a subsurface image from the further updated physical properties model.