Page 68 - Environmental Control in Petroleum Engineering

5§ Environmental Control in Petroleum Engineering

Naturally Occurring Radioactive Materials

Naturally occurring radioactive materials (NORM) are found virtu-
ally everywhere on the earth, including ground and surface waters
(Judson and Osmond, 1955). During the production of oil and gas,
radioactive materials that naturally occur within the earth can be
coproduced. Although the concentrations of NORM are usually very
low, these materials can be concentrated during production; the con-
centrated levels can become high enough to cause a health hazard if
improperly managed.
There are four radionuclides most commonly found in NORM in
the upstream petroleum industry: radium-226, radium-228, radon-222,
and lead-210. Radium-226 is probably the nuclide with the greatest
potential for environmental impact for the petroleum industry. Other
radioactive materials are also found, but in significantly lower amounts.
Radium (both 226 and 228) is highly soluble and is produced as a
dissolved solid with the produced water. The levels of radium in
produced water vary significantly. Although most wells do not produce
significant amounts of NORM, typical concentrations in wells having
NORM have been reported to vary between 1-2,800 picocuries per
liter (pCi/1). Much higher concentrations, however, have also been
reported (St. Pe et al., 1990; Miller et al., 1990; Snavely, 1989;
Stephenson, 1992). In comparison, the natural radium levels in surface
waters are typically less than 1 pCi/1. Drinking water standards for
radioactive materials are typically 5 pCi/1, and discharge standards for
open water are 30 pCi/1, although these regulatory limits can vary.
Radium is coprecipitated with barium, calcium, and strontium
sulfate as scale in tubulars and surface equipment during production.
This concentrates the radium and makes the scale radioactive. Radium
can also be concentrated in various production sludges through its
association with solids in the sludge. NORM concentrations of several
hundred thousand pCi/gm have been found in scale in piping and
surface equipment. Concentrations in excess of 8,000 pCi/gm have
been measured in the soil at pipe cleaning yards (Carroll et al., 1990).
The presence of NORM, however, can be easily identified with gamma
ray detectors.
Radon-222 is a naturally occurring gas that is found in some
produced water and natural gas liquids. This gas comes out of solution
as the pressure is reduced during production. Because it is a gas, it