Shale compensated radioactive well log - with simultaneously measured gamma ray counts in hydrogen and chlorine characteristic bands

摘要

Bursts of high energy neutrons are emitted during a measurement portion of an operating cycle, to produce a succession of thermal neutron populations in a borehole. Gamma radiation is detected in a wide energy range including the capture gamma ray spectrum of all elements, during first and second detection time intervals in each measurement portion. Additionally, gamma radiation in a first energy sub-range including the capture gamma ray spectrum of hydrogen and gamma radiation in a second energy sub-range including the capture gamma ray spectrum of chlorine are both detected throughout the measurement portion. From the radiation detected in the first and second detection intervals the macroscopic thermal capture cross-section of the formation is determined. Simultaneously, the relative presence of hydrogen and chlorine is determined from the respective sub-range measurements. The detector of the logging instrument is shielded with material having a thermal neutron capture gamma emission spectrum within the first energy sub-range and outside the second. More precise measurements allowing easier interpretation which are less subject to errors are obtd.