A New Short Borehole Logging Tool

A new borehole surveying tool was used to log the deep borehole at Camp Century, Greenland in July 1992. This new 6.35cm diameter instrument has a length of only 1m, allowing it to pass through bends in the sometimes highly deformed boreholes. The fluid filled borehole was logged to within 35m of bedrock, at a slant hole depth of 1350m. The inclination approached or exceeded 30^o several times in the lower portion of the borehole. A microprocessor controlled data acquisition package (DAP) measures an internal and external thermistor and two orthogonally mounted inclinometers. The pressure transducer, which also includes a temperature measurement, and the fluxgate compass have independent microprocessor systems which are multiplexed through the DAP. A coaxial cable supplies DC power from the surface to the logger and provides MODEM communications between the DAP and a personal computer on the surface where the data from the DAP and slant hole depth data from the winch are used to compute a directional survey of the borehole. The surface computer provides plots of temperature, fluid pressure, hole inclination and azimuth as a function of true vertical depth as the hole is being surveyed. A set of centering springs can be easily added at the ends of the logging tool for use in boreholes where the inclination is less than 1 degree.