Real time filtering in nuclear well logging and the like

Radiant energy – Geological testing or irradiation – Well testing apparatus and methods

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G01V 500

Patent

active

045688290

ABSTRACT:
Disclosed are a method and a system for well logging in which gamma radiation detected in five energy windows is converted into logs of formation thorium, uranium and potassium (Th,U,K), and of borehole barite and potassium chloride (KCl), in a process which makes use of an adaptive filter which accounts for changes in the detected gamma radiation with borehole depth, for the nature of the logging process, and for the composition of the borehole fluid. In a first, simpler embodiment, the filter is based on changes with borehole depth in the total amount of detected gamma radiation in the vicinity of the depth level of interest. In a second, more exacting embodiment, the filter is based on both the vertical variations in the Th,U,K concentrations, and the statistical variations in the measurements. In both embodiments a log of Th,U,K is produced. A third embodiment is based on the second but additionally incorporates the effect of the borehole size and the influence of the gamma ray emitters and absorbers in the borehole fluid on the detected counts of the energy windows. The third embodiment permits the converting of the received radiation information into logs of formation thorium, uranium and potassium, and borehole barite and potassium chloride, by borehole depth. The invention relates to induced as well as natural gamma radiation, and to other types of well logging in which energy windows can be measured.

REFERENCES:
patent: 3521064 (1970-07-01), Moran et al.
patent: 3976878 (1976-08-01), Chevalier et al.
Marrett et al., "Shaly Sand Evaluation Using Gamma Ray Spectrometry, Applied to the North Sea Jurassic," Proc. SPWLA 17th Annual Logging Symp., Jun. 9, 1976.
Serra et al., "Theory Interpretation and Practical Applications of Natural Gamma Ray Spectroscopy," Proc. SPWLA 21st Annual Logging Symp., Jul. 8, 1980.
Ellis, "Correction of NGT* Logs for the Presence of KCl and Barite Muds," Proc. SPWLA 23rd Annual Conference, Jul. 6-8, 1982.
Schultz et al., "Applications of Digital Filtering Techniques to Nuclear Well Logs," SPWLA 22nd Annual Logging Symp., Jun. 23-26, 1981, pp. 1-13.

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