Carbon/oxygen (C/O) logging instrumentation

An instrument system has been developed for field measurement of the relative carbon content of reservoir rocks. Gamma rays produced by inelastic scattering of 14-MeV neutrons are detected and analyzed in a sophisticated scintillation spectrometer system adapted for routine commercial well logging. A pulsed-neutron source similar to those in commercial use for other nuclear logs is employed. A van de Graaff generator provides the accelerating voltage to initiate the deuterium-tritium reaction, which produces the neutrons in a specially designed ion acceleration tube. Pulses from the radiation detector are transmitted to the surface over a conventional seven-conductor logging cable without degrading the spectrum. The log is available on a limited commercial basis and is recommended for identifying oil- saturated zones in cased wells where formation water is too fresh for reliable application of the Neutron Lifetime Log. (U.S.)