COMPARING BOTTOM-HOLE TEMPERATURE CORRECTION METHODOLOGIES IN THE MESOZOIC STRATA OF SOUTH TEXAS FOR TEMPERATURE-DEPTH MAPPING AND GEOTHERMAL PLAY TYPE IDENTIFICATION

Bottom-hole temperature (BHT) measurements from well logs are an abundant data set in sedimentary basins but are also notoriously unreliable because of several reasons associated with their acquisition. These reasons include the vintage of the measurement, type of tool used, ambient surface temperature at the time of logging, thermal properties of the drilling mud, time since circulation (TSC), rate of penetration (ROP) while drilling, human error, and the thermal conductivity of the formation and formation fluids (oil, natural gas, or brine) where the temperature is measured. Consequently, BHT correction methods vary depending on the basin and available data.

For this project, four different correction methodologies were applied to a dataset of 272 wells in south Texas with BHT measurements in Mesozoic formations. Each of these wells also have digital well logs, TSC data, BHT measurements and their associated depths, and the ambient surface temperature at the time of logging. Depths for these BHT measurements range from approximately 6,000 ft to 24,000 ft and uncorrected temperatures range from 145⁰ F to 435⁰ F. Using the Waples correction method resulted in an average increase in BHT of 19.66% and the Forster method had a similar average temperature increase of 20.49%. The SMU-Harrison and Kehle correction formulas resulted in an average temperature increase of 12.44% and 14.86% respectively.

To calibrate the accuracy of these different correction methods, temperature measurements from 10 cement bond logs (CBLs) and 22 cased-hole temperature logs for these wells was compared to the corrected temperatures values. Between 6,000 ft and 12,000 ft, corrected BHT measurements from each method fall within the trend of calibration temperatures from both CBLs and cased-hole temperature logs. However, below 12,000 ft, the Waples and Forster methods tend to calculate higher temperatures compared to the CBLs and cased-hole temperature logs. These two methods appear to be overestimating the temperature at deeper depths, while the SMU-Harrison and Kehle methods may be underestimating temperatures in the deeper parts of the basin. Consequently, developing intra-basin specific BHT correction methods may be necessary to correct for geologic and drilling variables that affect the true formation temperature, which is a pivotal part of geothermal exploration in sedimentary basins.