A very detailed and complete thermal dataset collected from well 58-32 at the Milford-Utah FORGE site allows testing of methods to extrapolate equilibrium temperatures when the drilling is stopped for 24 hours. During short drilling breaks to measure deviation of the hole, maximum reading thermometer measurements were taken at approximately 300 ft (90 m) intervals. However, these measurements proved to be poor indicators of bottom-hole temperature because the thermometer was about 30 m above the bit and therefore a relatively long thermal recovery time due to the effects of mud circulation. When the drilling was stopped at 2073 m (6800 ft) and the drilling rods were pulled out of the hole, the circulation time at the bottom of the hole was estimated to be 2 ± 0.5 hours. Four logging runs to obtain bottom-hole temperatures were then run over a period of 24 hours. The mud circulation temperature at the bottom of the hole was close to 60°C when drilling stopped, and the temperature rose from 130 to 160°C over the subsequent 24 hours. A temperature log of the hole after 37 days showed the near-equilibrium temperature was 181°C at this depth. The temperature logs at 2073 m showed the vertical temperature difference over the lowermost 30 m varies between 11°C at 8.1 hours and 6°C after 24.2 hours, explaining why the effects of drilling disturbance are too large to estimate for all depths except for a few meters at the bottom of the hole. An unexpected result from each of the four logging runs at 2073 m was that temperatures at the bottom of the hole rose by 5–8°C over 4–8 minutes while the probe was stationary. This is attributed to radial temperature gradients in fluid in the hole that disappeared due to mixing effects caused by probe movement. These effects were not seen in the 37-day logging run because the fluid had presumably come to equilibrium with the drill hole walls. The most reliable estimate of equilibrium temperature was obtained by using measurements after 12 hours and extrapolating using traditional Horner methods. The best-fit trendline for the 12-24 hours values predicted the 37-day temperature to within a few degrees Celsius. The slope of the thermal recovery line of 280°C/thermal recovery unit on a natural log plot is similar to that derived from several other exploration wells around the Roosevelt Hot Spring system, suggesting this may be a characteristic of bottom-hole temperatures in wells drilled into granite with a 8.75 inch diameter bit.

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