Elastic impedance estimation for inversion of far offset seismic sections
First Claim
1. A method of operating a computer to perform an inversion of seismic survey traces associated with a plurality of midpoints in a survey region, and obtained over a plurality of offset distances, comprising the steps of:
- retrieving well log data including compressional velocity, shear velocity, and density data, over depth for at least one well location in the survey region;
selecting a first angle of incidence;
generating an elastic impedance model using the compressional velocity, shear velocity, and density log data and dependent upon the first angle of incidence;
retrieving, from memory, seismic survey data for a plurality of midpoints in the survey region having offset distances at or near the first angle of incidence;
stacking the retrieved seismic survey data by midpoint;
performing an inversion of the stacked retrieved seismic survey data according to the generated elastic impedance model, to generate a first impedance section for the survey region associated with the first angle of incidence;
combining the first impedance section with a low-frequency impedance model associated with the first angle of incidence, to generate a first merged impedance model for the survey region associated with the first angle of incidence;
selecting a second angle of incidence;
repeating the generating, retrieving, stacking, performing, and combining steps to generate a second merged impedance model for the survey region associated with the second angle of incidence; and
producing a survey of rock properties in the survey region using a comparison of the first and second merged impedance models at corresponding depth points.
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Abstract
A computer-implemented method, and system implementing the method, of performing impedance inversion of seismic survey data are disclosed. Sonic and density well logs are used to generate an elastic impedance model, at selected angles of incidence or offset range, using an expression for elastic impedance that depends upon the measured or estimated compressional velocity, shear velocity, and density of the subsurface layers in the survey region. The elastic impedance expression also includes a reference density value, and is dependent upon the ray parameter (or angle of incidence). This elastic impedance model is used, for example by way of a pseudo-density log, in estimating the input wavelet, and in carrying out an impedance inversion of the seismic survey over the entire survey region, for at least two angles of incidence. Low-frequency components of the elastic impedance, at the selected angles of incidence, are merged with the corresponding impedance inversion sections, to produce a merged impedance model at the selected angles of incidence. Rock properties, such as Poisson'"'"'s ratio, are then retrieved from a comparison, such as a ratio, of the impedance traces at the varying angles of incidence for common midpoints.
81 Citations
19 Claims
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1. A method of operating a computer to perform an inversion of seismic survey traces associated with a plurality of midpoints in a survey region, and obtained over a plurality of offset distances, comprising the steps of:
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retrieving well log data including compressional velocity, shear velocity, and density data, over depth for at least one well location in the survey region; selecting a first angle of incidence; generating an elastic impedance model using the compressional velocity, shear velocity, and density log data and dependent upon the first angle of incidence; retrieving, from memory, seismic survey data for a plurality of midpoints in the survey region having offset distances at or near the first angle of incidence; stacking the retrieved seismic survey data by midpoint; performing an inversion of the stacked retrieved seismic survey data according to the generated elastic impedance model, to generate a first impedance section for the survey region associated with the first angle of incidence; combining the first impedance section with a low-frequency impedance model associated with the first angle of incidence, to generate a first merged impedance model for the survey region associated with the first angle of incidence; selecting a second angle of incidence; repeating the generating, retrieving, stacking, performing, and combining steps to generate a second merged impedance model for the survey region associated with the second angle of incidence; and producing a survey of rock properties in the survey region using a comparison of the first and second merged impedance models at corresponding depth points. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A computer-readable memory having a storage medium configured so that, when read and used by a computer, the computer is directed to perform an inversion of seismic survey traces associated with a plurality of midpoints in a survey region, and obtained over a plurality of offset distances, said computer directed by a plurality of operations comprising:
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retrieving, from a memory device, well log data including compressional velocity, shear velocity, and density data, over depth for at least one well location in the survey region; selecting a first angle of incidence; generating an elastic impedance model using the compressional velocity, shear velocity, and density log data and dependent upon the first angle of incidence; retrieving, from a memory device, seismic survey data for a plurality of midpoints in the survey region having offset distances at or near the first angle of incidence; stacking the retrieved seismic survey data by midpoint; performing an inversion of the stacked retrieved seismic survey data according to the generated elastic impedance model, to generate a first impedance section for the survey region associated with the first angle of incidence; combining the first impedance section with a low-frequency impedance model associated with the first angle of incidence, to generate a first merged impedance model for the survey region associated with the first angle of incidence; selecting a second angle of incidence; repeating the generating, retrieving, stacking, performing, and combining steps to generate a second merged impedance model for the survey region associated with the second angle of incidence; and producing and storing, in a memory device, a survey of rock properties in the survey region using a comparison of the first and second merged impedance models at corresponding depth points. - View Dependent Claims (11, 12, 13, 14)
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15. A digital computing system for performing an inversion of seismic survey traces associated with a plurality of midpoints in a survey region, and obtained over a plurality of offset distances, comprising:
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a memory resource, for storing data corresponding to well log data including compressional velocity, shear velocity, and density data, over depth for at least one well location in the survey region, data corresponding to seismic survey data for a plurality of midpoints in the survey region, the seismic survey data corresponding to varying offset distances, and horizon data corresponding to the location of boundaries between adjacent formations in the survey region; a computer system output device; and a system computer, coupled to the memory resource and to the output device, for performing the operations of; retrieving well log data from the memory resource for at least one well location in the survey region; selecting a first angle of incidence; generating an elastic impedance model using the compressional velocity, shear velocity, and density log data and dependent upon the first angle of incidence; retrieving, from the memory resource, seismic survey data for a plurality of midpoints in the survey region having offset distances at or near the first angle of incidence; stacking the retrieved seismic survey data by midpoint; performing an inversion of the stacked retrieved seismic survey data according to the generated elastic impedance model, to generate a first impedance section for the survey region associated with the first angle of incidence; combining the first impedance section with a low-frequency impedance model associated with the first angle of incidence, to generate a first merged impedance model for the survey region associated with the first angle of incidence; selecting a second angle of incidence; repeating the generating, retrieving, stacking, performing, and combining steps to generate a second merged impedance model for the survey region associated with the second angle of incidence; and producing and forwarding, to the output device, a survey of rock properties in the survey region using a comparison of the first and second merged impedance models at corresponding depth points. - View Dependent Claims (16, 17, 18, 19)
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Specification