On the Method of temperature Measurements in Borehole Using Precision thermometers

Abstract

Precise autonomous borehole thermometers (loggers) allow measuring temperature anomalies of small amplitude (up to 1 mK). It significantly expands the range of problems that borehole thermometry can solve in exploration geophysics, hydrogeology, engineering geology, and geoecology. However, thermal logging techniques remain outdated that hinders the effective implementation of the capabilities of these devices. The paper discusses methodological issues of precision temperature measurements in water-filled boreholes. Experimental studies with an autonomous thermometer rBrsolo³ T (RBR Ltd., Canada) showed that the device’s response to changes in ambient temperature (relaxation) is complex. Within a few seconds after the immersing of device in a borehole, it registers a temperature close to the fluid temperature. However, this temporary “window” closes soon, and after 15–20 seconds the measured temperature begins to deviate more and more from the undisturbed temperature. Next time measured temperature returns to the undisturbed temperature after 1000–6000 sec. In addition, the temperature response in the interval of 20–600 sec is complicated by non-periodic fluctuations with an amplitude of 0.02–0.05 K associated with thermal convection. The presence of a time “window” on the relaxation curve makes it possible to measure fluid temperature quickly and accurately in stop-and-go mode. The design parameters of thermometers determining the width of the “window” were assessed using mathematical modeling. Recommendations for conducting precision temperature logging of boreholes in both continuous and stop-and-go modes have been provided.