**2.1. Radon**

One of the decay products of U238 is Rn222, a radioactive noble gas. Radon emanates from the ground where it can be breathed in. Radon also decays to alpha-emitting progeny nuclides, so inhaling a single radon atom can lead, ultimately, to up to four alpha decays in the lungs before reaching stability. Since radon comes from the decay of geologic uranium, radon concentrations will vary according to local geology. In general, radon dose will be higher in areas that are underground, poorly ventilated, and in areas with high levels of uranium in the rocks.

Crude oil or gas is considered the most important sources of natural radionuclides from the uranium and thorium series. The radionuclides of primary concern to the oil and gas industry Overview about Different Approaches of Chemical Treatment of NORM and TE-NORM Produced from Oil Exploitation http://dx.doi.org/10.5772/61122 87

**Figure 1.** The origins of NORM in the recovery process [1]

materials containing enhanced levels of natural radionuclides, which are summarized as TE-NORM (technologically enhanced naturally occurring radioactive materials). Naturally occurring radionuclides are present at varying concentrations in the Earth's crust and can be concentrated and enhanced by processes associated with the recovery of oil and gas. This "enhanced'' NORM, often known as TE-NORM, can be created as a result of industrial processes and human activity, and in addition, can be the by-product of oil, gas production. One of the important examples that can contain elevated levels of NORM, and the radioactive materials may migrate from site to site as the materials and equipment are reused are sludge,

Transportation or decay of radioactive elements produces other radionuclides (daughters) from the reservoir to the surface with the produced oil and gas carried out under certain conditions dependent upon pressure, temperature, acidity. NORM with the oil, gas, and water mixture migrate and accumulate in scale, sludge, and scrapings during the production process. Moreover, they form a thin film on the interior surfaces of gas-processing vessels and equip‐ ment. The geological formation is considered as important parameters at determining the level of NORM and it was found that the accumulation can vary from one site to another depending

Alpha particles are considered as internally hazardous if a radioactive source of alpha-emitting particles is inhaled or ingested. While beta particles have one (negative) charge and interact more slowly with the material, they are effectively stopped by thin layers of metal, wood, or plastic and considered hazardous only if a beta-emitter source is ingested or inhaled. Gamma emitters are associated with alpha, beta decay with high-energy electromagnetic radiation that interacts lightly with matter. Gamma rays are best shielded by thick layers of lead or other dense materials and are considered as an external hazard to human bodies. Figure 1 details

One of the decay products of U238 is Rn222, a radioactive noble gas. Radon emanates from the ground where it can be breathed in. Radon also decays to alpha-emitting progeny nuclides, so inhaling a single radon atom can lead, ultimately, to up to four alpha decays in the lungs before reaching stability. Since radon comes from the decay of geologic uranium, radon concentrations will vary according to local geology. In general, radon dose will be higher in areas that are underground, poorly ventilated, and in areas with high levels of uranium in the

Crude oil or gas is considered the most important sources of natural radionuclides from the uranium and thorium series. The radionuclides of primary concern to the oil and gas industry

pipe scales, produced water, and drilling mud.

⋅ Alpha (α) ⋅ Beta (β) ⋅ Gamma (γ)

the origins of NORM in the recovery process [1].

**2. Natural Radionuclides in the Oil Industry**

There are three types of radiation emitted by NORM, namely:

on it.

86 Advances in Petrochemicals

**2.1. Radon**

rocks.

are Ra226 (U238 decay) and Ra228 (Th232 decay) due to their radiotoxicity and relatively long half-lives (1620 and 5.75 years, respectively) as shown in Figures 2 and 3 [1]. Radon radionu‐ clides escaping from the adjacent geological formations are soluble in crude oil, but due to its half-life (3.825 days) only Rn222 is

present in the pumped oil in varying concentrations from 10 to 800 Bq/kg [1]. Many previous data on the distribution of the main radon nuclide Rn222 in different gas fields and processing plants were collected in the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) report [2]. Crude oil is usually pumped to the surface together with produce water with radon and radium radionuclides while uranium and thorium usually do not go into solution. Various cations such as barium and strontium, with anions such as sulfate, chloride, or the bicarbonate solubility of radon in water is lower, and the level of Rn222 concentrations in the petroleum formation water was found in the range of 18.5 Bq/dm3 [3]. Very low concentrations measured for the U and Th and produced waters were obtained under the reducing conditions. The same result was found with radium nuclides released by alpha from the surrounding minerals or leaching processes usually recovered by sorption, except for saline waters with high concentration of chloride anions [4–5]. Typical ranges or average values of the radium radionuclide concentrations in the formation or produced water from different oil fields, including the recent data, are listed in Table 1.

**Figure 2.** Uranium238 decay series [1]

The worldwide average concentration of these radionuclides in produced water discharged to the environment is estimated at 10 Bq/l. These concentrations are approximately three orders of magnitude higher than the natural concentrations of radium in drinking or sea water.

Scale formation is a complex phenomenon and can be interpreted by the variation of the solubility of carbonates or sulfates or by pressure and temperature changes, water injection into the reservoirs, and evaporation in the gas extraction pipes. Radium and radon concen‐ trations in the pipe scale and waste sludge are dependent on three factors: the amount of Ra present in the subsurface soil, treatment processes applied during oil or gas production, and formation of water components. Most radium radionuclides are efficiently concentrated from the water phase during formation of the scale. Therefore, the measured levels of activity concentrations both in the separated sludge and in the solid scale are much higher than those Overview about Different Approaches of Chemical Treatment of NORM and TE-NORM Produced from Oil Exploitation http://dx.doi.org/10.5772/61122 89

**Figure 3.** Thorium232 decay series [1]

The worldwide average concentration of these radionuclides in produced water discharged to the environment is estimated at 10 Bq/l. These concentrations are approximately three orders of magnitude higher than the natural concentrations of radium in drinking or sea water.

**Figure 2.** Uranium238 decay series [1]

88 Advances in Petrochemicals

Scale formation is a complex phenomenon and can be interpreted by the variation of the solubility of carbonates or sulfates or by pressure and temperature changes, water injection into the reservoirs, and evaporation in the gas extraction pipes. Radium and radon concen‐ trations in the pipe scale and waste sludge are dependent on three factors: the amount of Ra present in the subsurface soil, treatment processes applied during oil or gas production, and formation of water components. Most radium radionuclides are efficiently concentrated from the water phase during formation of the scale. Therefore, the measured levels of activity concentrations both in the separated sludge and in the solid scale are much higher than those

measured in the produced water from the oil industry. Ra226 and Ra228 activity concentrations measured in the solid scale and sludge are listed in Table 2.



**Table 1.** Ranges of activity levels in produced water from the oil fields


**Table 2.** Ranges of activity levels of 226Ra in different scale and sludge samples

From the data obtained in Table 2, it was found that the concentration levels of radium nuclides in sludge were much lower than those of the scale. Environmental Protection Agency (EPA) estimated the average radium nuclide concentration to be around 2800 Bq/kg and 18, 000 Bq/ kg in sludge and scale, respectively [32]. The exposure is caused by external radiation coming from the 226Ra radionuclide and its progenies: Pb214 and Bi214 as well as by inhalation of αemitting radionuclides; Rn222 as well as Po218 and Po214 formed from Rn222 escaping into the air adjacent to scale deposits, see Table 3.

The main types of scales encountered in oil and gas facilities are sulfate scale such as BaSO4, which is called barite. Colorless or milky white is the common one, but can have any color, depending on the impurities trapped in the crystals during barite formation. The high density of barite is responsible for its value in many applications. It is always chemically inert and Overview about Different Approaches of Chemical Treatment of NORM and TE-NORM Produced from Oil Exploitation http://dx.doi.org/10.5772/61122 91


**Table 3.** Exposure rate levels in the oil industry

insoluble. Due to the high chemical similarity of radium with barium (Ba), strontium (Sr), and calcium (Ca), radium co-precipitates with Sr, Ba, or Ca scale forming radium sulfate, radium carbonate, and in some cases radium silicate is produced. As mentioned before, the mixing of seawater, which is rich in sulfate, with the produced water, which is rich in Cl–1, increases the scaling tendency. In addition, any change in pressure and temperature or acidity of the formation water contributes to scale build-up. The build-up of scale on the interior of a pipe is shown in Figure 4. The activity concentrations of Ra226 and Ra228 in hard scales in Egypt and some other countries were mentioned in Table 4.

**Figure 4.** The build-up of scale on the interior of a pipe

**228Ra (Bq/dm3**

a: Mean activity concentration.

**228Ra (Bq/dm3**

90 Advances in Petrochemicals

**) 226Ra (Bq/dm3**

**) 226Ra (Bq/dm3**

15.400–76.100 25.000

**Table 1.** Ranges of activity levels in produced water from the oil fields

the air adjacent to scale deposits, see Table 3.

**Table 2.** Ranges of activity levels of 226Ra in different scale and sludge samples

**) Sample Field**

12.6a Oilfield brine USA [18] 22–30 Produced water USA [19]

**) Sample Field** 5.1–14.8 Formation water Algeria [7–8]

23a 17a Produced water Australia [9] 0.05–12 0.01–6 Produced water Brazil [10] 1–59 5.1a Produced water Congo [11] - 5–40 Formation water Egypt [12] 2.8a 0.2-2 Produced water Italy [11] 0.5–21 0.3–10.4 Formation water Norway [12] 8.8–60.4 3.3a Produced water Norway [13] - 0.5–16 Produced water Norway [14] - 9.9-111.2 Produced water Syria [15] 0.7–1.7 1.7a Produced water UK [16] 15.1a 0.1–60 Produced water USA [6] 25–30 0.15–21.6 Produced water USA [17]

From the data obtained in Table 2, it was found that the concentration levels of radium nuclides in sludge were much lower than those of the scale. Environmental Protection Agency (EPA) estimated the average radium nuclide concentration to be around 2800 Bq/kg and 18, 000 Bq/ kg in sludge and scale, respectively [32]. The exposure is caused by external radiation coming from the 226Ra radionuclide and its progenies: Pb214 and Bi214 as well as by inhalation of αemitting radionuclides; Rn222 as well as Po218 and Po214 formed from Rn222 escaping into

The main types of scales encountered in oil and gas facilities are sulfate scale such as BaSO4, which is called barite. Colorless or milky white is the common one, but can have any color, depending on the impurities trapped in the crystals during barite formation. The high density of barite is responsible for its value in many applications. It is always chemically inert and

USA [31] Australia [9]

Scale Sludge

> Inhibitors may be applied to the piping complexes to prevent scales from slowing the oil extraction process. If the scales contain TE-NORM, the radiation will remain in solution and eventually be passed on to the produced waters. The United States generated annually around 100 tons of scale per oil well. Sometimes, in some cases brine is introduced into the produced water to enhance the recovery of radium; this also increases scale formation.


**Table 4.** Activity of 226Ra (U-series), 228Ra (U-series), and 40K in the TE-NORM in Egypt and some countries
