Donald W. Oliver

The Continuous Carbon/Oxygen Log Basic Concepts and Recent Field Experiences

The continuous carbon/oxygen (C/theta) log, recorded by a 20-kHz pulsed neutron logging tool, locates and quantitatively evaluates hydrocarbon reserves in cased wellbores independent of the salinity of formation waters. Gamma rays emitted during neutron inelastic scattering and neutron capture provide information on relative amounts of several elements in potential reservoirs, such as C, theta, silicon (Si), calcium (Ca), etc. These data can be related to oil saturation of reservoir rocks of fresh, mixed, or unknown formation water salinities and to formation lithology. Measurement principles, tool response, test pit data, and interpretive concepts are summarized. Field case examples include hydrocarbon exploration behind pipe, monitoring of production wells, secondary and tertiary recovery schemes, evaluation of heavy oil reservoirs, tar sands, and steamfloods, and other case studies in clastic carbonate reservoirs.