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Underground Injection Control Branch Guidance No. 5 wysiwyg://35/http://www.epa.gov/reg5oh2o/uic/r5_OS.htm ~. ~. • i the natural geothermal gradient can be of great value in assisting later analyses and for unders[anc other geophysical effects. B. Advantages and Disadvantages of Temperature Logging Informational Advantages Relative to Other Log Tvoes: ~ Continuous log with high vertical resolution ~ The most sensitive indicator of part 2 of MI In addition to fluid movement within [he well bore, fluid migration through the confining layers may be identified ~ Water-filled porosity can be determined if sufficient information is available Informational Disadvantages Relative to Other Lo Tg voes: Gas entry may be marked by cooling, but movement and exit may be obscure ~ Interpretation for complete understanding requires a greater degree of expertise than other logging methods Operational Advantages Relative to Other Log Types: Injection pressure need not be maintained to ensure identification of well bore flow near th injection interval Flow need not be occurring at the time of logging for its effects to be identifiable ~ Low cost per single survey covering entire well bore Operational Disadvantages Relative to Other Log Tvoes: Fluid-filled well bore through interval to be tested may be required ~ Well must be shut in long enough to remove most constmction and near-well bore effects C. Equipment and Reporting Forms The temperature logging tool is a wireline sonde operated from a winch truck. Temperature loggi tools contain circuitry which responds to temperature change by changing resistance to current flt The response is linear and temperature logs can distinguish very small changes in temperatures. Calibration of logging tools is often poor because the effects they are normally expected to mean have importance as relative rather than absolute values, although correct absolute temperatures al have value for other purposes. To be effective, temperature logging tools must have good therms: coupling to [he borehole environment, which means that [hey are not generally useful in air-filled holes. Sampling is done at short intervals as the sonde is lowered into the well, so that a record o1 entire well bore is produced. Because the tool does not react to temperature change instantaneous and the tool is continuously moving, [he measured temperature changes lag actual wellbore temperature changes by a consistent amount. The more slowly the tool moves, the closer are the measured temperatures to actual temperatures. If the tool speed is erratic, the recorded temperatul profile will also be irregular. Despite the possible inaccuracies due to poor calibration and tool response time, the absolute values recorded can generally be compared with some confidence. The log is the normal reporting form. All necessary information can be placed on the log. This includes: logging speed, time since the last injection, and temperature of the liquid most recently injected. If there are frequent changes in the temperature of the injectate or if process changes hay caused a significant change in the temperature of the injectate, it is very important to record the average temperatures of [he injectate before existing logs were made and the date of [he change it injectate temperature and the volume of liquid injected before and since that time. 19 0(34 5/2R/99 I :09 PM