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Supreme Service & Specialty Co. of Houma, La., has introduced a natural gamma (N/G) sub that, it says, is a viable and more cost-effective option to tightly regulated radioactive-tagged (R/A) subs.
The tag markers of the N/G sub are comprised of a low, natural radioactive source that renders it exempt from stringently controlled Nuclear Regulatory Commission regulations, Supreme says. The new sub can be used in any R/A sub application, including tubing conveyed perforating or the setting of sump packers and downhole assemblies, according to Supreme.
Supreme says the N/G sub, when used in conjunction with a gamma-ray scintillation tool, will provide approximately 200 to 600 gamma-ray counts/sec, as compared to 3,600 to 5,000 counts/sec with the conventional R/A material. With normal downhole formations emitting anywhere from 10 to 90 background counts/sec, Supreme says the N/G sub will provide “more than sufficient” counts for locating exact depth in the wellbore.
The N/A sub, Supreme says, does not come with the regulatory headaches of a typical R/A sub, which, owing to its high radioactive level, requires operators to exhaust every option to retrieve the sub, should it become lost downhole or in transit. If an R/A sub, which is lost downhole, cannot be fished out, operators run the costly risk of losing the wellbore. 
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