A Method for Improving the Accuracy of Elemental Weight Fractions Measured by Pulsed Neutron Spectroscopy Logging
J. Liu, S. Liu, F. Li, F. Zhang and B. Miao
Event name: 80th EAGE Conference and Exhibition 2018
Session: Petrophysics I
Publication date: 11 June 2018
Info: Extended abstract, PDF ( 442.28Kb )
Price: € 20
Formation elemental composition and mineralogy are essential for the evaluation of oil and gas reservoir. Pulsed neutron spectroscopy well logging technology is playing a crucial role in determining elemental concentration, identifying lithology and improving the evaluation of matrix properties. The accuracy of elemental concentration is important to the determination of other parameters. Standard spectra of individual elements, which can be obtained by experimental measurement, are the base data to process the neutron induced gamma ray spectroscopy. For a specific instrument, the standard spectra libraries utilized are fixed. By using Monte Carlo numerical modelling, the standard gamma ray spectra of individual elements under different conditions are calculated. The results show variation of borehole size, drilling mud types and other logging conditions have impacts on the shape of the standard libraries. Therefore, when processing the measured data with a set of fixed standard spectra, the accuracy of elemental concentration is affected. To address this problem, a model for compensating the effect of logging condition on the shapes of standard spectra is proposed. An field example is illustrated to validate the proposed method and results show that the agreement between computed elemental weight fractions and core analysis values is improved.