Criteria to Determine Borehole Formation Temperatures for Calibration of Basin and Petroleum System Models
Production test and drillstem test (DST) temperatures based on high flow volumes of oil or water from the producing formation are generally the most reliable temperature data for calibration of basin and petroleum system models. However, the down-hole gauge must be located within or near the formation and gas production zones should be avoided because of the Joule-Thompson effect. Long-term static tests are also generally reliable, but they are rare. Bottom-hole temperatures (BHT) from well log headers are common, but require correction because they are biased lower than true formation temperature. Care must be taken to avoid short static times, re-circulation 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 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 Petromod® one-dimensional 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 (1,001 ft) above and 6.2 my earlier or 231 m (758 ft) below and 4.5 my later than that calculated using a corrected BHT formation temperature of 92.4°C. In summary, BHT data are an important source of uncertainty that needs to be considered when calibrating basin and petroleum system models.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009