Efficient Method For Inversion of Geophysical Data
First Claim
1. A computer-implemented method for inversion of measured geophysical data to determine a physical properties model for a subsurface region, comprising:
- (a) obtaining a group of two or more encoded gathers of the measured geophysical data, wherein each gather is associated with a single generalized source or, using source-receiver reciprocity, with a single receiver, and wherein each gather is encoded with a different encoding function selected from a set of non-equivalent encoding functions;
(b) summing the encoded gathers in the group by summing all data records in each gather that correspond to a single receiver (or source if reciprocity is used), and repeating for each different receiver, resulting in a simultaneous encoded gather;
(c) assuming a physical properties model of the subsurface region, said model providing values of at least one physical property at locations throughout the subsurface region;
(d) inverting the measured geophysical data, one simultaneous encoded gather at a time, using the assumed physical properties model as an initial model, and iteratively updating said model to minimize a cost function measuring degree of misfit between model-simulated data and the measured geophysical data to generate an updated physical properties model, wherein model adjustments are made using a gradient of the cost function with respect to at least one model parameter, which gradient is computed from a time integration of a product of encoded simultaneous-source data simulated forward in time and encoded simultaneous-source data simulated backward in time; and
(e) downloading the updated physical properties model or saving it to computer storage.
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Abstract
A method for efficient inversion of measured geophysical data from a subsurface region to prospect for hydrocarbons. Gathers of measured data (40) are encoded (60) using a set of non-equivalent encoding functions (30). Then all data records in each encoded gather that correspond to a single receiver are summed (60), repeating for each receiver to generate a simultaneous encoded gather (80). The method employs iterative, local optimization of a cost function to invert the encoded gathers of simultaneous source data. An adjoint method is used to calculate the gradients of the cost function needed for the local optimization process (100). The inverted data yields a physical properties model (110) of the subsurface region that, after iterative updating, can indicate presence of accumulations of hydrocarbons.
59 Citations
19 Claims
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1. A computer-implemented method for inversion of measured geophysical data to determine a physical properties model for a subsurface region, comprising:
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(a) obtaining a group of two or more encoded gathers of the measured geophysical data, wherein each gather is associated with a single generalized source or, using source-receiver reciprocity, with a single receiver, and wherein each gather is encoded with a different encoding function selected from a set of non-equivalent encoding functions; (b) summing the encoded gathers in the group by summing all data records in each gather that correspond to a single receiver (or source if reciprocity is used), and repeating for each different receiver, resulting in a simultaneous encoded gather; (c) assuming a physical properties model of the subsurface region, said model providing values of at least one physical property at locations throughout the subsurface region; (d) inverting the measured geophysical data, one simultaneous encoded gather at a time, using the assumed physical properties model as an initial model, and iteratively updating said model to minimize a cost function measuring degree of misfit between model-simulated data and the measured geophysical data to generate an updated physical properties model, wherein model adjustments are made using a gradient of the cost function with respect to at least one model parameter, which gradient is computed from a time integration of a product of encoded simultaneous-source data simulated forward in time and encoded simultaneous-source data simulated backward in time; and (e) downloading the updated physical properties model or saving it to computer storage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 19)
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18. A method for inversion of measured geophysical data from a subsurface region to prospect for hydrocarbons, comprising:
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(a) obtaining a group of two or more encoded gathers of the measured geophysical data, wherein each gather is associated with a single generalized source or, using source-receiver reciprocity, with a single receiver, and wherein each gather is encoded with a different encoding function selected from a set of non-equivalent encoding functions; (b) summing the encoded gathers in the group by summing all data records in each gather that correspond to a single receiver (or source if reciprocity is used), and repeating for each different receiver, resulting in a simultaneous encoded gather; (c) assuming a physical properties model of the subsurface region, said model providing values of at least one physical property at locations throughout the subsurface region; (d) inverting the measured geophysical data, one simultaneous encoded gather at a time, using the assumed physical properties model as an initial model, and iteratively updating said model to minimize a cost function measuring degree of misfit between model-simulated data and the measured geophysical data to generate an updated physical properties model, wherein model adjustments are made using a gradient of the cost function with respect to at least one model parameter, which gradient is computed from a time integration of a product of encoded simultaneous-source data simulated forward in time and encoded simultaneous-source data simulated backward in time; and (e) using the updated physical properties model to prospect for hydrocarbons in the subsurface region.
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Specification