Precision continuous temperature logging and comparison with other types of logs

摘要: For a variety of well environments, continuous temperature logs at different speeds, taken with appropriate equipment and fast time‐response probes, can yield temperature data often reproducible to several hundredths of a degree centigrade. Larger differences in reproducibility (several tenths of a degree centigrade) probably result from changes in the well bore. Below the liquid level, data need not be filtered through time‐response characteristics of the probe to give accurate geothermal gradients (typically ± a few percent) that correlate with lithology. Resulting temperature‐gradient logs are qualitatively correlated to other logs, such as induction‐conductivity, gamma‐ray, seismic, bulk‐density, and lithologic logs. Qualitative correlation with the induction‐conductivity log appears best. Temperature gradients generally increase when other logs indicate the formation is becoming shaly or clayey (less sandy, silty, or limy), and/or less competent. The practical worth of the temperature‐gradient log may be its ability to sense formation properties inside casing and tubing. This characteristic of the temperature‐gradient log may allow lithologic identification in shut‐in wells and permit useful logging after casing has been set.