Spectral gamma-ray logging II: borehole correction factors

Conference · Mon Jan 01 04:00:00 EST 1979

OSTI ID:6035143

Wilson, R D; Stromswold, D C; Evans, M L; Jain, M; Close, D A

Experimentally determined factors are presented that correct spectral gamma-ray logs for the effects of varying borehole fluid and casing attenuation. These corrections are for gamma-ray spectra from the naturally radioactive isotopes of K, U, and Th. A sodium iodide spectral gamma-ray probe was used to collect data on the 1.46-MeV gamma ray from /sup 40/K, the 1.76-MeV gamma ray from /sup 214/Bi (a decay product of /sup 238/U), and the 2.61-MeV gamma ray from /sup 208/Tl (a decay product of /sup 232/Th). Count rates for these gamma rays were measured for various borehole fluid and casing conditions. Borehole fluid corrections are presented for both centralized and sidewalled probe geometries for hole diameters from 3 to 12 inches. For a typical hole diameter of 4.5 inches and a probe diameter of 2.0 inches, the water correction is 23 percent for the potassium signal, and 15 percent for the uranium and thorium signals. For the smaller borehole diameters, the water correction is nearly independent of probe placement. As the borehole diameter increases to 12 inches, the correction for the uranium and thorium signals increases to 50 percent for the sidewalled geometry and to 100 percent for the centralized geometry. Gamma-ray transport calculations were performed to predict the effects of borehole water for the centralized probe geometry, and the resulting water factor corrections are somewhat lower than the measured values. The difference is attributed to the fact that detector response has not yet been included in the calculations. Casing corrections are presented for dry boreholes with thicknesses of steel casing from 1/16 inch to 1/2 inch. The data are fit reasonably well with exponential curves having effective linear attenuation coefficients of 1.26 inch/sup -1/ for U and 1.03 inch/sup -1/ for Th. 12 figures, 9 tables.

• Research Organization: Bendix Field Engineering Corp., Grand Junction, CO (USA); Los Alamos Scientific Lab., NM (USA)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 6035143
• Report Number(s): LA-UR-79-1053; CONF-790605-5
• Country of Publication: United States
• Language: English

Related Subjects

440400 -- Well Logging Instrumentation
47 OTHER INSTRUMENTATION
58 GEOSCIENCES
580203* -- Geophysics-- Geophysical Survey Methods-- (1980-1989)
ACTINIDES
ALKALI METALS
ALLOYS
BOREHOLES
CAVITIES
CORRECTIONS
DRILLING FLUIDS
ELEMENTS
ERRORS
GAMMA LOGGING
GAMMA SPECTRA
HYDROGEN COMPOUNDS
IRON ALLOYS
IRON BASE ALLOYS
METALS
OXYGEN COMPOUNDS
POTASSIUM
RADIOACTIVITY LOGGING
SPECTRA
STEELS
THORIUM
URANIUM
WATER
WELL CASINGS
WELL LOGGING