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Re-Evaluation of Bottom-Hole Temperature Corrections: New Insights From Two Hot Wells in West-Central Utah


The in situ thermal regime in oil and gas exploration wells has often been assessed using Horner-type corrections, although numerous alternative empirical techniques have also been used. A common obstacle for many of these methods is the fact that critical data required to make an accurate correction to the drilling-disturbed temperature are rarely recorded. In the Pavant Butte 1 well, drilled by ARCO Oil and Gas Co. in 1981, geophysical logging at several depths allowed us to construct a geotherm based on Horner-type corrections. The geotherm indicated a temperature of 230 ± 10°C at the total depth (TD) of 3300 m. We subsequently received a previously confidential equilibrium temperature profile measured when Phillips Geothermal re-entered the well in 1984, three years after it was plugged and abandoned. The observed temperature at the bottom of the casing at 2133 m is 15°C hotter than previously predicted, and the temperature is estimated to be 250°C at TD. Ascencio et al. (2006) have shown from spherical-radial theory that transient temperatures at TD display a linear T versus 1/√time behavior, with an intercept equal to the undisturbed formation temperature. These authors comment that Horner-type corrections appear to under-estimate the equilibrium temperature. Their simple correction technique does not appear to have been used in the petroleum literature. The opportunity to test the accuracy of the Horner-type correction and the Ascencio et al. method became available in a geothermal exploration well drilled in August-September of 2017. Four transient temperatures measured over 24 hours at an interim TD of 2073 m imply an equilibrium temperature of 185 ± 10°C using the Horner-type correction and 196 ± 10°C using the Ascencio et al. method. An equilibrium profile will be measured in this new well in November of 2017, approximately eight weeks after the well was shut-in, and will be compared with these predictions.