Iterative inversion of data from simultaneous geophysical sources
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 signature selected from a set of non-equivalent encoding signatures;
(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) calculating an update to the assumed physical properties model that is more consistent with the simultaneous encoded gather from step (b), said calculation involving one or more encoded simultaneous source forward or reverse simulation operations that use the assumed physical properties model and encoded source signatures using the same encoding functions used to encode corresponding gathers of measured data, wherein an entire simultaneous encoded gather is simulated in a single simulation operation;
(e) repeating step (d) at least one iteration, using the updated physical properties model from the previous iteration of step (d) as the assumed model to produce a further updated physical properties model of the subsurface region that is more consistent with a corresponding simultaneous encoded gather of measured data, using the same encoding signatures for source signatures in the simulation as were used in forming the corresponding simultaneous encoded gather of measured data; and
(f) downloading the further updated physical properties model or saving it to computer storage.
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Abstract
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.
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Citations
26 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 signature selected from a set of non-equivalent encoding signatures; (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) calculating an update to the assumed physical properties model that is more consistent with the simultaneous encoded gather from step (b), said calculation involving one or more encoded simultaneous source forward or reverse simulation operations that use the assumed physical properties model and encoded source signatures using the same encoding functions used to encode corresponding gathers of measured data, wherein an entire simultaneous encoded gather is simulated in a single simulation operation; (e) repeating step (d) at least one iteration, using the updated physical properties model from the previous iteration of step (d) as the assumed model to produce a further updated physical properties model of the subsurface region that is more consistent with a corresponding simultaneous encoded gather of measured data, using the same encoding signatures for source signatures in the simulation as were used in forming the corresponding simultaneous encoded gather of measured data; and (f) downloading the further 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, 18, 19)
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20. 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 signature selected from a set of non-equivalent encoding signatures; (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) simulating a synthetic simultaneous encoded gather corresponding to the simultaneous encoded gather of measured data, using the assumed physical properties model, wherein the simulation uses encoded source signatures using the same encoding functions used to encode the simultaneous encoded gather of measured data, wherein an entire simultaneous encoded gather is simulated in a single simulation operation; (e) computing a cost function measuring degree of misfit between the simultaneous encoded gather of measured data and the simulated simultaneous encoded gather; (f) updating the physical properties model by optimizing the cost function; (g) iterating steps (a)-(f) at least one more time using the updated physical properties model from the previous iteration as the assumed physical properties model in step (c), resulting in a further updated physical properties model; and (h) downloading the further updated physical properties model or saving it to computer storage. - View Dependent Claims (21, 22)
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23. 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 signature selected from a set of non-equivalent encoding signatures; (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) selecting an iterative series solution to a scattering equation describing wave scattering in said subsurface region; (e) beginning with the first n terms of said series, where n≧
1, said first n terms corresponding to the assumed physical properties model of the subsurface region;(f) computing the next term in the series, said calculation involving one or more encoded simultaneous source forward or reverse simulation operations that use the assumed physical properties model and encoded source signatures using the same encoding functions used to encode corresponding gathers of measured data, wherein an entire simultaneous encoded gather is simulated in a single simulation operation and the simulated encoded gather and measured encoded gather are combined in a manner consistent with the iterative series selected in step (d); (g) updating the model by adding the next term in the series calculated in step (f) to the assumed model; (h) repeating steps (f) and (g) for at least one time to add at least one more term to the series to further update the physical properties model; and (i) downloading the further updated physical properties model or saving it to computer storage.
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24. 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 measured geophysical data from a geophysical survey of the subsurface region; (b) inverting the measured data by iterative inversion involving simultaneous 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 simulation are encoded, resulting in a simulated simultaneous encoded gather of geophysical data, the inversion process involving updating an assumed physical properties model to reduce misfit between the simulated simultaneous encoded gather and a corresponding simultaneous encoded gather formed by summing gathers of measured survey data encoded with the same encoding functions used in the simulation; and (c) downloading the updated physical properties model or saving it to computer storage.
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25. A method for producing hydrocarbons from a subsurface region, comprising:
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(a) performing a seismic survey of the subsurface region; (b) obtaining a velocity model of the subsurface region determined by a method comprising; inverting measured survey data by iterative inversion involving simultaneous simulation of the seismic survey data representing a plurality of survey sources, or receivers if source-receiver reciprocity is used, wherein source signatures in the simulation are encoded, resulting in a simulated simultaneous encoded gather of geophysical data, the inversion process involving updating an assumed velocity model to reduce misfit between the simulated simultaneous encoded gather and a corresponding simultaneous encoded gather of measured survey data encoded with the same encoding functions used in the simulation; (c) drilling a well into a layer in the subsurface region identified at least partly from an interpretation of structure in the subsurface region made using the determined velocity model; and (d) producing hydrocarbons from the well.
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26. A computer program product, comprising a non-transitory computer usable medium having a computer readable program code embodied therein, said computer readable program code adapted to be executed to implement a method for inversion of measured geophysical data to determine a physical properties model for a subsurface region, said method comprising:
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(a) inputting 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 signature selected from a set of non-equivalent encoding signatures; (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) inputting 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) simulating a synthetic simultaneous encoded gather corresponding to the simultaneous encoded gather of measured data, using the assumed physical properties model, wherein the simulation uses encoded source signatures using the same encoding functions used to encode the simultaneous encoded gather of measured data, wherein an entire simultaneous encoded gather is simulated in a single simulation operation; (e) computing a cost function measuring degree of misfit between the simultaneous encoded gather of measured data and the simulated simultaneous encoded gather; (f) updating the physical properties model by optimizing the cost function; and (h) iterating steps (a)-(f) at least one more time using the updated physical properties model from the previous iteration as the assumed physical properties model in step (c), using a same or different set of non-equivalent encoding signatures for each iteration, resulting in a further updated physical properties model.
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Specification