Walter Fertl, Dresser Petroleum Engineering Services
Carbon/Oxygen (C/O) logging applicable in cased wellbores measures energy and intensity of inelastic and capture gamma rays resulting from pulsed neutron irradiation of subsurface formations. Continuous C/O logs therefore define the relative abundance of elements, such as C, 0, Si, Ca, H, etc., which in turn relates to lithology, porosity, and hydrocarbon saturation distribution in potential reservoir rocks independent of formation water salinities. Basic concepts and environmental correction will be reviewed with special emphasis being placed on practical field experiences both in sandstone and carbonate reservoirs. Such field applications include exploration for bypassed oil in old wells, location and monitoring of oil in low or unknown formation water salinities, monitoring sweep and displacement efficiency of waterfloods and EOR projects, residual oil determination, evaluation of heavy oil and tar sand reservoirs, etc.