Radon (Rn-222) and thoron (Rn-220) emanation fractions from three separate formations of oil field pipe scale



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Texas A&M University


Over the course of normal oil well operations, pipes used downhole in the oil and petroleum industry tend to accumulate a mineral deposit on their interior, which restricts the flow of oil. This deposit, termed scale, will eventually occlude the interior diameter of the pipe making removal from service and descaling a cost effective option. The pipes are sent to cleaning yards where they remain until descaling can be performed. This storage period can potentially create a health concern not only because of the external radiation exposure but also because of the radon gas emissions, both of which are due to the radioactive minerals contained in the scale. It was believed that the structure of the scale is formed tightly enough to prevent much of the radon from becoming airborne. The goal of this research was to determine the emanation fractions for the rattled scale samples from three formations. A high purity germanium detector was used to measure the activities of the parents and progeny of radon, and electret ion chambers were used to measure the concentration of radon emanated from the scale. The emanation fractions of between 4.9x10-5 and 1.08x10-3 for radon were a factor of approximately 100 smaller than previous research results. For thoron, the fractions were and 5.72x10-8 and 4.92x10-7 for thoron with no previous research to compare. However, information that pertains to the temperature dependence of emanation was included in this research and was not available for previous, similar research. Therefore, differences in the environment (e.g., temperature, humidity, etc.) in which the previous experiments were conducted, as well as differences in the scale formation types used, could account for the discrepancy. In addition, measuring the emanation fractions of the rattled scale was a method of determining whether surface to volume ratio dependence existed. After acquiring the emanation fractions, insufficient evidence of any surface to volume ratio dependence could be found.