Natural gamma ray spectroscopy applied to borehole measurements

Conference · Mon Feb 01 04:00:00 EST 1988 · IEEE Trans. Nucl. Sci.; (United States)

OSTI ID:7181736

Gadeken, L L; Smith, Jr, H D; Arnold, D M; Robbins, C A

This paper describes current techniques for performing natural gamma ray spectroscopy measurements in borehole environments. The data were obtained using the system known as the Compensated Spectral Natural Gamma tool which uses the complete energy spectrum to provide information on the borehole environment in addition to concentrations of potassium (K), uranium (U) and thorium (Th) in the formation. Elemental concentrations are estimated from count rates in thirteen selected energy ranges (windows) using the method of weighted-least-squares which incorporated real-time compensation for borehole effects. This is accomplished by using an attenuation model which accounts for count rate reduction and spectral shape changes due to borehole absorption and scattering. The use of a low atomic number toolcase allows gamma rays in the low energy, photoelectrically sensitive part of the spectrum to be transmitted to the detector. The system gain stabilizer operates in a coincidence mode so that formation gammas incident on the detector can be separated from those which originate in the /sup 241/Am stabilization source. This low energy data is processed into ratios of Compton and photoelectric window count rates. The ratio in uncased holes is optimized to provide qualitative indications of lithology and changes in lithology. A similar ratio in cased wells gives diagnostic information regarding the condition of the steel tubulars in the borehole. Two examples demonstrate the presentation of the logs and the quality of the results.

• Research Organization: Welex, P.O. Box 42800, Houston, TX (US)
• OSTI ID: 7181736
• Report Number(s): CONF-871006-
• Conference Information: Journal Name: IEEE Trans. Nucl. Sci.; (United States) Journal Volume: 35:1
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
& Exploration
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400102 -- Chemical & Spectral Procedures
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
ALPHA DECAY RADIOISOTOPES
AMERICIUM 241
AMERICIUM ISOTOPES
DETECTION
EQUIPMENT
EXPLORATION
EXPLORATORY WELLS
GAMMA DETECTION
GAMMA LOGGING
GAMMA SPECTRA
GAMMA SPECTROSCOPY
GEOLOGIC DEPOSITS
GEOLOGIC MODELS
HEAVY NUCLEI
ISOTOPES
MEASURING INSTRUMENTS
MINERAL RESOURCES
MINERALOGY
NATURAL GAS DEPOSITS
NATURAL RADIOACTIVITY
NUCLEI
ODD-EVEN NUCLEI
PETROLEUM DEPOSITS
RADIATION DETECTION
RADIATION DETECTORS
RADIOACTIVITY
RADIOACTIVITY LOGGING
RADIOISOTOPES
RESERVOIR ROCK
RESOURCES
SPECTRA
SPECTROSCOPY
WELL LOGGING
WELL LOGGING EQUIPMENT
WELLS
YEARS LIVING RADIOISOTOPES