Probe response and continuous temperature measurements

Abstract

A platinum temperature transducer moving at a constant speed in a drill hole gives a temperature that is the convolution of the true temperature and the impulse response of the transducer. The true temperature function appearing in the convolution integral can be determined by inverse filtering, and accurate thermal gradients can be obtained by using moving probes that are not in thermal equilibrium. Layered sections composed of layers from 1 to 15 meters thick, with thermal conductivities varying from 5 mcal/cm sec °C to 15 mcal/cm sec °C were synthesized. Large apparent heat-flow anomalies associated with a probe not in equilibrium and moving through the layered media at a constant speed of 0.5 meter/sec were examined. From a laboratory determination of the time response of the probe to a step change in temperature, an inverse filter can be designed that, when convolved with the measured temperature profile, gives the true temperature and thus gives correct thermal gradients. The proposed method of recovering the true temperature gradient would result in a continuous equilibrium temperature gradient with greater resolution and with no sacrifice in logging time. Small variations in a continuous log of thermal conductivity, especially in sedimentary sections, can be of value in stratigraphic correlation and interpretation.