Method and apparatus for spectroscopic analysis of a geological formation

摘要

Earth formations surrounding a well borehole are analyzed by obtaining a series of capture gamma ray spectra representative of the interaction of thermal neutrons with various chemical elements in the formation surrounding a borehole. The capture gamma ray spectra are used to determine spectral elemental yields quantitatively indicative of the relative abundance of various chemical elements present in the formation. These yields are recorded as a function of depth in said borehole to produce a plurality of traces. The relative sensitivities of the logging tool to a number of the formation components, such as sandstone and limestone, are predetermined either from tool responses in the borehole plus core measurements or from tool responses in a laboratory formation plus the known makeup of the laboratory formation. The volume fractions of the formation components surrounding the well borehole are then determined from the spectral elemental yeilds and the predetermined relative sensitivities and are recorded as a function of depth to generate a tangible record which graphically illustrates the formation lithology.