Comprehensive Application Of Dual Detector Carbon/Oxygen Spectral Log

At present, Carbon/Oxygen spectral log is an effective method widely used in monitoring oil saturation variation in cased hole, and can provide abundant information. The variation of remaining oil is evaluated with the information, and it provides the basis for development of oil field.Since few methods for shale content and porosity have been applied, quantitative evaluation on old wells with no porosity log can not be done. Six effective shale content indicators are chosen to solve the above problems on the basis of theory analysis and comparison of Carbon/ Oxygen spectral logs and shale content curves in the paper. The result shows Silicon / Calcium and lithology-indicator ratio curves are optimum shale content indicators. Six methods for shale content are proposed. Based on pervasion theory, pervasion equation and relationship between moderation length of neutron and porosity, and based on absorbed effect, absorption equation of gamma-ray photon and relationship between density with porosity, it theoretically shows that it is linear relation between capture spectrum count rate ratio of near and far detector or inelastic scattering spectrum count rate ratio of near and far detector and porosity. Comparison of Carbon/ Oxygen spectral logs and porosity curves shows that capture spectrum count rate ratio of near and far detector is an optimum porosity indicator. Five methods for total porosity and effective porosity are proposed. Water saturation models including borehole effect for Carbon/Oxygen spectral log are given. Also, the methods to determine shale content, porosity and saturation are established with logs in open hole. The result shows that interpretation precision is good. Comparison of remaining oil saturation determined from Carbon/Oxygen spectral log and that from resistivity log is done to achieve the dynamic evaluation of remaining oil in reservoirs.