Geophysical technology for determining the ground parameters (methods and apparatus)

Abstract

At the Institute of Geophysics of the National Academy of Sciences of Ukraine a modern technology for ground investigation has been created for solution of the engineering geological problems, including seismic microzonation. Technology is based on the methods and apparatus of radioactive logging (RL), which involves neutron-neutron logging (NNL), gamma-gamma density logging (DL) and gamma-ray logging (GR). The paper presents the results of the development of radioactive logging apparatus as an integral part of the new technology. Set of prototype dual-channel tools, namely 2NNL (dual-spacing NNL) and DL+GR, prototype three-component tool 2NNL+DL+GR, surface control and registration console were developed and produced on the basis of the modern elemental base. The 2NNL tool makes it possible to determine neutron porosity in two ways: single-sonde method and compensation method. Compensation neutron logging, in particular, aims to determine the porosity in the presence of anomalous neutron absorbers in the rock, and also, in combination with the single-sonde method, to estimate the content of anomalous absorbers. GR-channel of the DL+GR tool was equipped the same gamma-ray detector as the DL-channel. Here, the GR-detector performs a dual function: 1) integral registration of natural gamma-ray of ground, 2) account of natural background in the total readings of the DL-detector. The three-component radioactive logging tool combines three RL-methods and includes all the advantages of dual-channel tools. The obtaining a results in one trip by this tool is particularly important for relatively deep boreholes. According to the experimental results, the optimal intervals between sources and detectors of radiation in the created combined RL tools were established. The importance of adjustment and controlling the signals of sensors of the RL tools is shown; the new console allows to perform these procedures operational. The created apparatus increases the productivity and efficiency of logging operations by reducing the number of trips, digital recording, storage and transmission of information, and by using of a computer programs for processing and interpreting the results of borehole measurements. The effectiveness of the developed apparatus, together with the appropriate metrological and interpretation-methodical support, has been demonstrated on specific examples of borehole investigations and confirmed by independent laboratory data. The technology allows to determine the following engineering geophysical parameters: total density, dry ground density, content of shale, porosity, volume moisture, water saturation factor, groundwater level, etc.