A ROBUST RAPID-RESPONSE PROBE FOR MEASURING BOTTOM-HOLE TEMPERATURES IN DEEP-OCEAN BOREHOLES

A new probe has been constructed for making temperature measurements 1 .1 m ahead of the bit in Ocean Drilling Program (ODP) boreholes. Tempe ratures are recorded at positions 1 and 11 cm above the tip of the pro be. The combination of the dual temperature records and accelerometer data provides valuable information about disturbances that may affect the quality of measurements. Long battery life, and memory access via an external communications port, allow service-free operation for the full duration of typical drilling legs. Temperature resolution varies over the 110 K measurement range, from nominally 1 mK from -5 to 20 de grees C, to about 10 mK at 105 degrees C. The small (8 mm) diameter of the probe tip allows rapid thermal equilibration after penetration. T he shallow (2.5 degrees), continuous taper of the lower part of the pr obe serves to reduce the tendency of the formation to be cracked when the tool is pushed into the formation. It is sufficiently robust, howe ver, to survive penetration into highly consolidated sediment and occa sional contact with igneous rock. The tool was used for a total of 44 bottom-hole temperature measurements between 38 and 573 meters below s eafloor (mbsf) during Leg 168, as well as for several logging runs in open holes. We anticipate adding a port in the tip to permit measureme nt of formation fluid pressure, and to enhance the utility of the tool for logging temperature profiles in open holes.