Verification of Oxygen Cross Section Data for Oil Well Logging Applications

Abstract

The carbon/oxygen logging tools used in the petroleum industry to determine the ratio of the number of carbon to the number of oxygen nuclei in the formation surrounding the tool, and in this way the oil to water ratio, relies on a good knowledge on the oxygen and carbon cross sections in particular. The objective of this work is to investigate the importance of the oxygen cross section with respect to the needs of the oil well logging applications, and to state the quality of the presently available evaluations. For a few typical oil well logging geometries the radiation transport calculations combined with the cross section sensitivity analyses were performed. The sensitivity profiles of the 3 to 7 MeV gamma rays in the detectors (roughly corresponding to the energy windows used for carbon and oxygen logging) with respect to the major nuclear reaction types of oxygen very obtained, indicating the nuclear data important for oil well logging. Finally, the FNS/JAERI Liquid Oxygen Time-of-Flight benchmark experiment, involving the measurement of the angular neutron spectra leaking from a 20 cm liquid oxygen slab, and covering the energy range relevant for oil well logging applications, was analysed in order to determine the actual state-of-the-art of the oxygen nuclear data. The benchmark experiment was analysed using the discrete ordinates transport code DORT and compared to the results of the Monte Carlo code MCNP-4B.

Keywords:

• well logging
• benchmark experiment
• transport calculation
• discrete ordinates method
• cross-sections
• sensitivity and uncertainty analysis