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SPWLA Publications

Paper 1981 vXXIIn4a1 :: Add Item

"In common with all physical measurements, logging tools are subject to measurement errors which require correction for detailed evaluations. In the experimental sciences, systematic components of variation are routinely differentiated from sources of error by regression analysis of variance. This approach may be incorporated as a log normalization procedure through the analysis of spatial variation within stratigraphic units which show only minor lateral changes in logging character. Log responses of these calibration units consist of a systematic component which is a function of geographic location, compounded with an error associated with the logging tool. Trend surface analysis is a form.of regression in which the spatial variation of a log response may be fitted by polynomial equations of geographic coordinates. These equations describe simple surfaces which are estimates of the normalized variation, while deviations of the raw data from the surfaces express tool error. A trend surface provides a predictive equation of normalized response which may be used in prognosis at existing well control and also at prospective drilling sites. The distribution of trend surface residuals is valuable in the diagnosis of relative precision and bias between separate tools and service companies, as well as highlighting potential problems of a unit as a calibration standard."