Geochemical loggingapparat and method for determining the concentrations of the formation of the elements in the vicinity of a borehole

摘要

Logging method and tool string for identifying and determining the concentrations of subsurface formation elements next to a borehole, by (i) using a low energy neutron source (either a chemical source, e.g. a 252Cf, or a deuterium-deuterium electronic source), and (ii) detecting and counting the delayed gamma rays resulting from the activation by the neutrons of atoms of at least one element of interest (e.g. aluminum). Two gamma ray detectors may also be disposed on either side of the low energy neutron source, for detecting and counting the prompt gamma rays resulting from the capture of neutrons by atoms of elements, such as Si, Ca, Fe, S, H, or Cl, Gd, Ti, or K. The low energy neutron source is used for both the "activation" and the "capture" measurements. The tool string may also include a natural gamma ray tool for the determination of uranium, thorium and potassium, and for measuring the background to be subtracted from the gross Al activation measurement. IMAGE