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Abstract

Bottom-hole temperatures (BHT) from well log headers are common, but they require correction because they are biased lower than true formation temperature. Care must be taken to avoid short static times, recirculation between measurements, and spurious records of times or temperatures from logs. Criteria for reliable Horner-corrected BHT data include a minimum of three logging runs that record time and temperature for each run, temperature extrapolation less than the range of temperature data, and deviations from the least-squares regression line that are less than measurement uncertainty (±1–3° C or ±2–5° F).

Based on published comparisons of drill-stem test (DST) and Horner-corrected BHT data from the same depths, the standard deviation of corrected bottom-hole temperatures is about ±8° C (± 14° F). Some studies show that corrected data may still be systematically biased lower than true formation temperature. For a one-dimensional PetroMod basin and petroleum system model of the upper Cook Inlet in Alaska, error of ±8° C resulted in calculated depth to top of the oil window in the Jurassic Tuxedni Group source rock of as much as 305 m (1001 ft) above and 6.2 million years earlier or 231 m (758 ft) below and 4.5 million years later than that calculated using a corrected BHT formation temperature of 92.4° C. Error in maturity assessment associated with shallow BHT data can propagate to the greater depth of the source rock where temperature and thermal maturity are to be estimated. In summary, BHT data are an important source of uncertainty that needs to be considered when calibrating basin and petroleum system models.

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