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Underground Injection Control Branch Guidance No. 5 ~wyg://35/http://www. epa.gov/reg5oh2o/u i c1r5_O5. htm activated oxygen moves closer to [he detector, and less if it moves away. By comparison of intent of gamma radiation measured as a result of activation at two detectors, the direction and velocity water movement can be determined. Studies under controlled conditions have shown that water velocities between two and 120 feet per minute can be measured. B. Advantages and Disadvantages Informational Advan[ape Relative to Other Log Tvoes: Interpretation is a simple comparison of a calculated velocity to a minimum velocity which tool is able to identify reliably Informational Disadvantages Relative to Other Log Types: ~ Can identify flow in a broad, but fixed, velocity range o Has a very small range of investigation, smaller than very large well bores ~ Cannot be used to demonstrate the absence of liquid movement through confining layers ~ It is not practical to increase vertical resolution by increasing spacing density Calibration errors may affect tool accuracy, perhaps accounting for false positive indicatior History includes false positives and missed MIT failures confirmed by one or more other tc Operational Advantages Relative to Other Log Types: Relative to temperature logs, little or no shut-in time is required o Does not require aliquid-filled well bore Numerical result eliminates the need for qualitative interpretation Operational Disadvantages Relative to Other Log Tvnes: ~ Injection pressure must be maintained to ensure identification of fluid flow near the injectit zone Actual logging time and cost are usually greater than for other logs C. Equipment and Forms The equipment consists of a wireline sonde containing ahigh-energy neutron generator and gamy ray detectors. By spacing several detectors at increasing distances from the oxygen activation are: interpretational accuracy is increased. Although the oxygen which is activated may be present in water which may be moving along the well bore, oxygen is also present in rock and cement. Som this oxygen is also activated, and its decay products become background radiation which must be accounted for in order to reach a valid measurement of the movement of activated atoms in the fl passing along the well bore. The need to account for oxygen which is not in flowing water can be addressed in either of two w 1) by making calibration measurements in a representative area of the well bore in which there is thought to be no flow behind the casing, or 2) by extending the measurement period at each static beyond the time during which the activated oxygen in flowing water has been carried away. The I of decay indicated by the late measurements is used to calculate the theoretical levels of gamma radiation which would have been measured if there were no water movement. The difference between the calculated and measured values is assumed to be the effect of the decay of activated oxygen carried [o the vicinity of the detectors as part of moving water. The first method is used by Western Atlas and the second by Schlumberger. These are [he only companies which provide oxygen activation logging service in Region 5. 24 of 34 528/99 I :09 PM