Monte Carlo simulation in nuclear geophysics: neutron logging in superdeep boreholes

Some years ago there were difficulties with well logging of superdeep borehole (SG-3) in Kola peninsula: (1) it was necessary to use the thick housing to protect tools at the depth of about 11 km; (2) the radioactive logs were dangerous because of the heavy tools and very long cable which could break off; and (3) any interpretation charts for Precambrian crystalline rocks were absent. A new logging tool, fixed on the drilling strings without a cable, was invented. The tool contains the sources and the detectors of the geophysical fields (e.g. radioactive) and the devices to store the logging data (the so-called self-contained tool). The radioactive sondes of the tool were optimized by the Monte Carlo simulation (MOK-package), and all interpretation charts and the correction factors were compared. The logging curves for SG-3 were interpreted to show the zones of interest. Later this tool was used very intensively for the logging of numerous horizontal boreholes. (author)