System and method for performing inversion on LWD resistivity logs with enhanced resolution
First Claim
1. A method for performing inversion resistivity on log data to determine a model formation, comprising:
- performing logging on a formation to obtain a resistivity log, wherein the resistivity log comprises log data;
selecting one or more control depths at one or more locations of each of a plurality of detected beds in the formation;
estimating the resistivity of each bed only at the selected control depths, wherein said estimating uses the log data, wherein said estimating produces an estimated resistivity for each of the beds;
computing a simulated log value at each control depth using a current estimate of the resistivity of the beds, wherein said computing uses said estimated resistivities at said selected control depths as an initial estimate of the true resistivity;
comparing the computed simulated log to the actual log data at each control depth;
adjusting the resistivity of each bed using the difference between the actual and simulated values at the control depths;
repeating said steps of computing a simulated log value at each control depth using the current estimate of the resistivity of the beds, comparing the computed log to the actual log at each control depth, and adjusting the resistivity of each bed using the difference between the actual and simulated values at the control depths, wherein said repeating is performed if the simulated log does not match the actual log at the control depths;
constructing a corrected log from the depths of the bed boundaries and the resistivity of each bed if the simulated log substantially matches the actual log at the selected control depths.
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Abstract
A system and method for performing inversion and for correcting for shoulder bed effect. The method enhances the resolution of wave propagation resistivity logs and corrects the logs for adjacent bed effects, whereby the resulting logs have a vertical response as good as wireline high-resolution induction logs. The method first performs logging while drilling on a formation to obtain LWD resistivity log data. The method then selects one or more control depths at one or more locations of each of a plurality of detected beds in the formation. The present invention includes a novel method for selecting bed boundaries from the log data, and the control depths are then determined based on the determined bed boundaries. The method then estimates the resistivity of each bed only at the selected control depths to produce an estimated resistivity of the beds. The method then computes a simulated log value at each control depth using a current estimate of the resistivity of the beds. The computed simulated log, is then compared to the actual log data at each control depth, and the resistivity of each bed is adjusted using the difference between the actual and simulated values at the control depths. The above method iteratively repeats a plurality of times until the simulated log substantially matches the actual log at the control depths.
90 Citations
40 Claims
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1. A method for performing inversion resistivity on log data to determine a model formation, comprising:
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performing logging on a formation to obtain a resistivity log, wherein the resistivity log comprises log data; selecting one or more control depths at one or more locations of each of a plurality of detected beds in the formation; estimating the resistivity of each bed only at the selected control depths, wherein said estimating uses the log data, wherein said estimating produces an estimated resistivity for each of the beds; computing a simulated log value at each control depth using a current estimate of the resistivity of the beds, wherein said computing uses said estimated resistivities at said selected control depths as an initial estimate of the true resistivity; comparing the computed simulated log to the actual log data at each control depth; adjusting the resistivity of each bed using the difference between the actual and simulated values at the control depths; repeating said steps of computing a simulated log value at each control depth using the current estimate of the resistivity of the beds, comparing the computed log to the actual log at each control depth, and adjusting the resistivity of each bed using the difference between the actual and simulated values at the control depths, wherein said repeating is performed if the simulated log does not match the actual log at the control depths; constructing a corrected log from the depths of the bed boundaries and the resistivity of each bed if the simulated log substantially matches the actual log at the selected control depths. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method for performing inversion resistivity on log data to determine a model formation, comprising:
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performing logging on a formation to obtain a resistivity log, wherein the resistivity log comprises log data; performing a curve fit of the log data after said performing logging while drilling; determining inflection points of the log data after said performing a curve fit of the log data; selecting bed boundaries from the inflection points of the curve-fit of the log data; selecting one or more control depths at one or more locations of each of a plurality of detected beds in the formation; estimating the resistivity of each bed only at the selected control depths, wherein said estimating uses the log data, wherein said estimating produces an estimated resistivity for each of the beds; computing a simulated log value at each control depth using a current estimate of the resistivity of the beds, wherein said computing uses said estimated resistivities at said selected control depths as an initial estimate of the true resistivity; comparing the computed simulated log to the actual log data at each control depth; adjusting the resistivity of each bed using the difference between the actual and simulated values at the control depths; repeating said steps of computing a simulated log value at each control depth using the current estimate of the resistivity of the beds, comparing the computed log to the actual log at each control depth, and adjusting the resistivity of each bed using the difference between the actual and simulated values at the control depths, wherein said repeating is performed if the simulated log does not match the actual log at the control depths; constructing a corrected log from the depths of the bed boundaries and the resistivity of each bed if the simulated log substantially matches the actual log at the selected control depths.
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23. A method for determining bed boundaries in a formation from resistivity log data, comprising:
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performing logging on a formation to obtain a resistivity log, wherein the resistivity log comprises log data; performing a curve fit of the log data after said performing logging while drilling; determining inflection points of the log data after said performing a curve fit of the log data; and determining bed boundaries from the inflection points of the curve-fit of the log data. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
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Specification