A New Digital Multiscale Pulsed Neutron Logging System

Abstract

Summary A new multiscale pulsed neutron capture logging system (PDKSM-100) is discussed. The instrument is a 11116-in. [1.7-cm] -diameter, microprocessor-controlled logging sonde that processes raw data occurring in the short-and long-spaced detectors. The timing spectrum (10 μsec per channel and 100 channels for the decay component) of the detector events is accumulated downhole and transmitted to the surface computer logging system upon command by a pulse code modulation data transmission system. This configuration makes use of significantly increased count rates to improve log repeatability greatly. Unique data reduction techniques are also possible with the high-resolution data. The gamma rays during the burst of 14-MeV neutrons are also processed. This unique feature allows derivation of the ratio of inelastic to capture count rates, which is a function of porosity. All conventional pulsed neutron capture (PNC) responses can be observed with the new pulsed neutron logging (PNL) system. However, many additional aspects of formation evaluation are possible as well. Several of the more unique features of the system are demonstrated in specific log examples.