Method of evaluating formations traversed by a borehole
First Claim
1. A method for obtaining an improved display of an output parameter trace over a depth interval indicative of geologic formation characteristics from borehole derived raw data, including the steps of:
- (1) deriving actual values of measurement parameters over said depth interval;
(2) assuming values for said output parameters over said depth interval;
(3) calculating theoretical values of said measurement parameters over said depth interval;
(4) displaying, over said depth interval, a trace of said assumed output parameters,(5) displaying, for said depth interval, in juxtaposition, representations indicative of a trace of said actual values, and a trace of said calculated theoretical values, whereby the degree of agreement between said trace of actual values and said trace of theoretical values is indicative of the reliability of said trace of output parameters.
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Accused Products
Abstract
A method which determines output parameters (such as porosity φ or water saturation Sw of formations) from a set of logging measurements taken at each level of a borehole is proposed.
Measurement and response equation uncertainties of each logging apparatus are determined at each measurement level. Assumed values of the output parameters are chosen and, applying the response equations, calculated values of the measurements are determined. The calculated values of the measurements and the actual measurements are then compared to determine deviations which are weighted by factors calculated from the previously determined uncertainties. An incoherence function is determined from the weighted deviations and a number of "a-priori" constraints. Minimization of the incoherence function gives the most probable output parameters whose uncertainty is in turn calculated. The computed values of the measurements are plotted alongside an indication of the range of uncertainty of the actual measurements for their comparison so as to provide an indication of the reliability of the derived output parameters, which are also plotted with or without their own range of uncertainties.
25 Citations
26 Claims
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1. A method for obtaining an improved display of an output parameter trace over a depth interval indicative of geologic formation characteristics from borehole derived raw data, including the steps of:
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(1) deriving actual values of measurement parameters over said depth interval; (2) assuming values for said output parameters over said depth interval; (3) calculating theoretical values of said measurement parameters over said depth interval; (4) displaying, over said depth interval, a trace of said assumed output parameters, (5) displaying, for said depth interval, in juxtaposition, representations indicative of a trace of said actual values, and a trace of said calculated theoretical values, whereby the degree of agreement between said trace of actual values and said trace of theoretical values is indicative of the reliability of said trace of output parameters. - View Dependent Claims (2)
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3. A method for obtaining an improved display of an output parameter trace over a depth interval indicative of geologic formation characteristics from borehole derived raw data, including the steps of:
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(1) deriving actual values of measurement parameters over said depth interval from said raw data; (2) assuming values for said output parameters over said depth interval from which are calculated theoretical values of said measurement parameters; (3) repetitively calculating different theoretical values of said measurement parameters from different assumed values for said output parameters until the value of an incoherence function has reached a minimum, said incoherence function being dependent on the differences between said actual values and said calculated theoretical values; (4) displaying, in the form of traces over said depth interval, in juxtaposition, the minimum values of said incoherence function and the corresponding assumed values of said output parameters.
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4. A method for obtaining an improved display of a trace representing the behavior of output parameters characteristic of the geologic formations over a depth interval traversed by a borehole, said method including the steps of:
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(a) physically logging said borehole depth interval by passing investigative logging tools through said borehole and recording the resultant raw data on formation characteristics and environmental conditions; (b) from said raw data, obtaining actual values over said depth interval for a plurality of measurement parameters; (c) deriving at least an equal plurality of response equations, each of which expresses a single measurement parameter as a function of one or more of said output parameters; (d) assuming values for each of said output parameters at a particular depth in said depth interval; (e) from said assumed values and said response equations, determining theoretical values for each of said measurement parameters; (f) repeating steps d and e to obtain optimum theoretical values for which the difference between the actual values and their respective theoretical values have been made optimally small; (g) repeating steps d, e and f for a plurality of different depths in said depth interval; (h) recording, for comparison, on a visually readable medium, a trace indicative of said actual values over said depth interval along with a trace over said depth interval of respective optimum theoretical values and also recording at least one trace over said depth interval comprising those assumed values of said output parameters which correspond to the recorded trace of optimal theoretical values, whereby the visually ascertainable degree of agreement between said trace of actual values and said trace of optimal theoretical values is indicated of the reliability of said at least one trace of assumed values. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. A method of obtaining an improved display of a trace over a depth interval of values of output parameters characteristic of the geologic formations traversed by a borehole, said method including the steps of:
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(a) generating signals indicative of actual values for a plurality of borehole and/or formation parameters; (b) deriving a plurality of response equations which functionally relate at least some of said formation parameters to said output parameters; (c) utilizing said response equations and assumed values of said output parameters to obtain signals indicative of calculated or theoretical values for each of said at least some of said formation parameters; (d) generating signals indicative of uncertainties for said responsive equations and for each of said at least some of said formation parameters; (e) generating signals indicative of the differences between said calculated or theoretical value signals and said actual value signals; (f) generating signals indicative of weighting factors dependent on said response equation uncertainty signals and said formation parameter uncertainty signals, said weighting factor signals being functionally related to the inverse of the sum of the squares of said uncertainty signals; (g) combining said difference signals and said weighting factor signals to generate an incoherence function signal functionally related to the sum of the squares of said difference signals and directly related to said weighting factor signals; (h) varying said assumed values of said output parameters until said incoherence signal has obtained a minimum value and generating output parameter signals indicative of the assumed values corresponding to said minimum incoherence signal; (i) recording on a medium a trace representation over said depth interval of an output parameter signal and a trace representation over said depth interval of said minimum incoherence function signal.
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Specification