A comparison of energy-window and spectral-fitting methods for the estimation of carbonate content in rocks using neutron-induced gamma rays

Conference · Sat Jun 01 00:00:00 EDT 1991

OSTI ID:5383910

Hearst, J R ^[1]; Conaway, J G ^[2]; Trcka, D E ^[3]; Grau, J A ^[4]

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1. Lawrence Livermore National Lab., CA (United States)
2. Los Alamos National Lab., NM (United States)
3. Atlas Wireline Services, Houston, TX (United States)
4. Schlumberger-Doll Research Center, Ridgefield, CT (United States)

When a nuclear explosive is tested underground, rock close to the explosion is heated to very high temperatures. If any of that rock contains carbonates, these are dissociated and the carbon may combine with oxygen to form carbon dioxide. When the rock cools, the carbon dioxide remains gaseous, possible causing subsurface pressures greater than atmospheric, which could increase the hazard of a delayed leak. To reduce that possibility, formations that might contain significant amounts of carbonates are analyzed for those materials. We have compared measurements of carbonate content from two commercial neutron-induced gamma-ray spectroscopy logging system in emplacement boreholes (2 to 4 m in diameter) at the Nevada Test Site (NTS). Both systems use high-energy neutrons to excite carbon and oxygen nuclei inelastically, and a spectrometer to detect the resulting gamma rays. One system uses broad energy windows around the main carbon and oxygen gamma-ray peaks and relates the carbonate content to the ratio of the two window count rates. This ratio requires correction for the gap between the sonde and the borehole wall, which is measured mechanically, and for the formation water content, which is obtained from a neutron log. The other system determines carbonate content by fitting the entire energy spectrum to a set of standard spectra reflecting the system response to pure elements in the formation. Water corrections are obtained directly from the spectroscopic measurements; no gap correction is needed. We tested both systems in a calibration facility to determine their responses to different values of carbonate, gap, and water content. They were then run in two boreholes at the NTS. Cuttings samples from both holes were analyzed for carbonate content for comparison with log results. 10 refs., 10 figs., 1 tab.

• Research Organization: Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: USDOE; USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5383910
• Report Number(s): UCRL-JC-106917; CONF-9108135-2; ON: DE91017660
• Resource Relation: Conference: 4. international Mineral and Geotechnical Logging Society (MGLS)/KEGS conference, Toronto (Canada), 18-22 Aug 1991
• Country of Publication: United States
• Language: English

Related Subjects

47 OTHER INSTRUMENTATION
45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE
ROCKS
GAMMA SPECTROSCOPY
UNDERGROUND EXPLOSIONS
GAMMA LOGGING
CARBON DIOXIDE
CARBONATES
COMPARATIVE EVALUATIONS
EXPERIMENTAL DATA
GAMMA RADIATION
GAMMA SPECTRA
NEUTRON REACTIONS
NEVADA TEST SITE
NUCLEAR EXPLOSIONS
BARYON REACTIONS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
DATA
ELECTROMAGNETIC RADIATION
EVALUATION
EXPLOSIONS
HADRON REACTIONS
INFORMATION
IONIZING RADIATIONS
NATIONAL ORGANIZATIONS
NUCLEAR REACTIONS
NUCLEON REACTIONS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
RADIATIONS
RADIOACTIVITY LOGGING
SPECTRA
SPECTROSCOPY
US DOE
US ORGANIZATIONS
WELL LOGGING
440400* - Well Logging Instrumentation
450200 - Military Technology
Weaponry
& National Defense- Nuclear Explosions & Explosives