In situ neutron capture spectroscopy of geological formations

Conference · Tue Jan 15 04:00:00 EST 1985 · AIP Conf. Proc.; (United States)

OSTI ID:5711029

Grau, J A; Antkiw, S; Hertzog, R C; Marente, R A; Schweitzer, J S

Neutron-capture-induced gamma-ray spectroscopy has been useful for determining the geological properties of porosity, lithology, and water salinity of the rock and fluid outside the iron casing which is cemented into most oil wells. This paper discusses such measurements using a pulsed source of 14-MeV neutrons and a NaI(T1) gamma-ray detector. The most difficult task in interpreting these measurements is to separate signals generated by elements in the formation rock and fluid from those due to elements inside the well bore. The physical properties at work here include fast-neutron thermalization times, thermal-neutron diffusion, competing neutron-capture cross sections, and gamma-ray transport to the detector. Results from studying the geophysical parameters which most affect these physical properties, porosity and water salinity, are presented here. Methods for enhancing the spectral contribution from the earth formation relative to that from the borehole are discussed. These include understanding the time dependence of the spectral shape, optimizing the source-to-detector spacing, and employing absorptive borehole fluid displacers.

• Research Organization: Schlumberger-Doll Research , Ridgefield, CT 06877
• OSTI ID: 5711029
• Report Number(s): CONF-840906-
• Conference Information: Journal Name: AIP Conf. Proc.; (United States) Journal Volume: 125:1
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580203 -- Geophysics-- Geophysical Survey Methods-- (1980-1989)
651100* -- Nuclear Physics-- Experimental Techniques-- (1980-)
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
BARYON REACTIONS
CAPTURE
CHEMICAL COMPOSITION
GAMMA SPECTROSCOPY
GEOLOGIC FORMATIONS
HADRON REACTIONS
LITHOLOGY
NEUTRON REACTIONS
NUCLEAR REACTIONS
NUCLEON REACTIONS
OIL WELLS
POROSITY
SALINITY
SPECTROSCOPY
WELLS