API PUBL 7102:1997 pdf download.Methods for Measuring Naturally Occurring Radioactive Materials (NORM) in Petroleum Production Equipment
Low concentrations of naturally-occurring radioactive materials tSOR-\.I) are sometimes carried from geologic formations into oil-Geld equipment as dissolved components of produced water. Under certain conditions these materials precipitate or otherwise accumulate in scales and sludges in oil and gas production equipment, and cause concentrations of radioactive elements that are significantly elevated above background levels. As awareness of this phenomenon has increased, so has the demand for more widespread radiation measurements and for instruments and methods that permit reliable measurements at lower concentrations. This report summarizes existing instrument technology for in-situ measurements of NORM, and describes a quantitative method for correlating instrument gamma radiation measurements with NORM concentrations. The correlations were developed from laboratory measurements and theoretical correlations and were benchmarked with field data.
Naturally-occurring radioactive materials are ubiquitous in the enlironment, and commonly occur in soils, water, food, and air. The NORM that accumulates in surface petroleum production equipment is predominantly radium-226 and radium-228 and their progeny, which come fmm the uranium-238 and thorium-232 decay chains, respectively (Figure 1-1). Both uranium and thorium occur naturally in underground formations and remain mostly in place. However, their radium decay products are slightly soluble, and under some conditions they become mobilized by liquid phases in the formation. When brought to the surface with liquid production streams these nuclides may remain dissolved at dilute levels, or may precipitate because of chemical changes and reduced pressure and at natural levels from the very large volumes of gas passing through the system. Since radon decays with a 3.8-day half life, the only nuclide remaining in gas-plant equipment that affects its disposal is lead-210, which has a 22-year half life. Lead-210 decays by beta emission, with only low-intensity, low-energy gamma rays.
The S ORiI 3ccumulated in production equipment scales typically contain radium coprecipitateci in barium sulfate and other very insoluble minerals. Sludges may contain mostly silicates or carbonates, but also incorporate trace radium by coprecipitation. Typically, radium-226 is in equilibrium with its decay products but radium-228 has sub- equilibrium decay products. Reduced concentrations of radium-228 daughters result from the occurrence in the thorium-232 decay chain of two radium nuclides separated by the 1.9-year half life thorium-228 (Figure 1-1). Both radium isotopes are usually considered together, since they are not distinguished by simple field measurements.