Research on Dual Mode Pulsed Neuron Spectral Logging Method and Its Application

Abstract

Pulsed neutron logging is one of the key techniques for monitoring residual oil saturation in the late stages of oilfield exploration. Dual mode pulsed neutron spectral logging is discussed, which can be used to obtain time spectra and energy spectra of inelastic scattering of gamma radiation during a borehole measurement. With optimized pulse radiation and measurement timing, the tool simultaneously measures Σ and C/O to calculate the residual oil saturation. In this paper, based on Monte Carlo numerical simulation, a mathematical model is proposed of the dependence of temporal and energy spectra of gamma radiation on reservoir parameters, and the characteristics of C/O and capture cross-section are calculated. An interpretation model is proposed that can be used to calculate oil saturation from the C/O-Σ cross-plots. Comparative analysis and field tests showed that dual mode PSL spectra make it possible to determinate residual oil saturation in an unknown porosity formation with increased accuracy, and have technological advantages over the single C/O energy spectrum and neutron lifetime logging.