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Underground Injection Comrol Branch Guidance No. 5 <br />~~~ . ~.. i <br />w y~yg://35/http://w ww.e pa.gov/reg5oh 2o/u i dr5_O5. h l m <br />interval to be checked for leaks. The RA material will mix with a portion of the injectate so [hat <br />slug of RA injectate passes through the section of the well to be tested. Any leak of the mixed <br />injectate will be marked with some RA tracer. The leaked tracer material may be traced using a <br />detector device on a wire line. The movement of the leaked tracer material is unlikely to keep pac <br />with the movement of the slug of marked injectate which continues down the well and will be <br />identifiable. <br />When tracer material is observed to split, the movement of the portion which appeazs to have <br />separated should be carefully traced. The most accurate way to do this is by positioning the detec~ <br />ahead of the moving tracer and observing its passage. When the tracer fails to arrive at the detects <br />[he upper limit of movement is fixed. This method is superior to chasing the slug because it appe: <br />to be more sensitive and the record does not distort the shape of the slug as a result of tool <br />movement. <br />B. Advantages and Disadvantages of the Radioactive Tracer Survey <br />Advantaee <br />Locates the depth of the leak within the well bore <br />Disadvantages <br />Expensive relative to SAI'T <br />Approved testing methods always require injection. Velocity shots used for the location of <br />small leaks may be used without injection, but require long periods of investigation <br />C. Equipment and Reporting Forms <br />The equipment required is readily available. In the past, almost any company engaged in geophys <br />logging was able to conduct RA tracer surveys. Some companies have discontinued the service d~ <br />to restrictions imposed on the handling of RA material. The equipment consists of a sonde (tool) <br />which is lowered into the well on a cable which allows transmission of data from the tool to recei <br />in a winch instrument truck on the surface. The tool consists of an injector stage, one or more gat <br />radiation detector devices, and a collar locator. <br />The relative positions of the injector and detectors are variable. If only one detector is used, it mu <br />be located below the ejector. If more than one is used, it is common and advantageous for one <br />detector to be located above the ejector. Three detectors are sometimes used with two being belo~ <br />the detector. This allows very accurate measurement of the speed of the injectate to be made. It al <br />simplifies the location of the upwazd limit of leaking by eliminating some repositioning of the for <br />The purpose of the collar locator is to pinpoint the location of leaks in reference to permanent <br />markers. This may also be done by means of correlation to a gamma ray trace which is scaled to <br />show lithologic effects. Using a collar locator immediately lets the analyst know whether an <br />identified leak is a[ a collar, while using a gamma ray correlation log clarifies the stra[igraphic <br />location of the leak. <br />The RA tracer is usually Iodine 131, because of its short (eight day) half life. Other tracers may b <br />used for special applications. [n any case, the tracer material used must be anionic to minimize its <br />molecular attraction to well and rock materials. <br />The only form required is the log of the test as presented by the service company which perfotme <br />13 of 34 5/28/99 1:09 PM <br />