"Only a crude estimate can be made of the annual total 226Ra activity transferred from oil reservoirs to the surface. A United States Environmental Protection Agency (US EPA) study of 10 oil production wells analysed scale and sludge production rates. (11) The amount estimated was about 250m3 for a period of 20 years. The resulting amount of waste generated by one oil-producing well per year is about 2.25 tons, using a waste density of 1.8 tonnes.m-3. In order to derive an average 226Ra activity concentration, the same study used results of a large number of external gamma readings (6,274) taken in several oil production facilities and converted these to the activity concentration. There is a significant uncertainty attached to such a procedure because of the effects of equipment wall thickness, self-absorption of the radiation in the scale and thickness of the scale, and distribution of radium within the scale. The published average radium concentration was 4.6Bqg-1. Hence, the resulting estimate of total 226Ra activity brought to the surface is 918GBq per year. Similar studies are due to be undertaken in oil and gas-extracting facilities in other parts of the world, so an average 226Ra activity brought to the surface per year can be derived with any degree of certainty."
http://www.touchoilandgas.com/radiological-impact-extraction-a97-1.html
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