Method for determining decay characteristics of multi-component downhole decay data
OwnerMedhat W. Mickaelinventor
Life of this patent
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Abstract
Measurements from many logging instruments such as Gamma ray counts from a pulsed neutron instrument, typically have a spectrum that contains a plurality of exponentially decaying components. The slowest decaying component is obtained by fitting a single exponential over the tail end of the data and selecting a beginning for the fitting window that minimizes the product of the chi-square and the standard error of the fit. The single determined component may be subtracted from the data and the process repeated to give additional components. The determined components are indicative of thermal neutron capture cross-sections.
Claims6
A method for determining a parameter of interest of a subterranean formation comprising:
- (a) conveying a logging tool into a borehole in said subterranean formation and using at least one detector on the logging tool to obtain measurements related to the parameter of interest, said measurements comprising at least two exponentially decaying components;
- (b) defining a plurality of starting times for analysis of said measurements;
- (c) fitting said measurements over a plurality of time windows between said starting times and a selected ending time, thereby defining a plurality of fits, said selected ending time being greater than each of said starting times;
- (d) determining a goodness of fit, a standard error of fit, and a product of said goodness of fit and said standard error of fit for each of the plurality of fits in (c);
- and
- (e) selecting a value from said plurality of starting times for which said product attains a minimum value.
Dependencies are inferred from the claim text.