Senv Guidelines for Management of Norm (1)

Annex I

GUIDELINES FORMANAGING NATURALLY OCCURRING

RADIOACTIVE MATERIALSIN PRODUCTION OPERATIONS

H. BASHAT, SENV Environmental Advisor

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Annex I

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Managing naturally occurring radioactive materials in production operations Annex I

GUIDELINES FOR MANAGING NATURALLY OCCURRING RADIOACTIVE MATERIALS (NORM) IN PRODUCTION OPERATIONS

SUMMARY

Naturally occurring radioactive materials, NORM, have been known to be present in varying concentrations in hydrocarbon reservoirs. These

NORM, under certain reservoir conditions can reach hazardous contamination levels. The recognition of NORM as a potential source of contamination to oil and gas facilities has become widely spread and gaining increased momentum from the industry. The contents of the Annex which wee extracted mainly from References 1 to 3, address the various problems with NORM and provides the recommended procedures for managing these materials.

INTRODUCTION

There are two types of NORM contamination which are commonly known in the oil and gas operations:

1) Radium contamination which is common to formation water and produces low specific activity scale known as LSA.

2) Radon contamination which is common to natural gas production.

Both of these elements when accumulate in significant concentration will form serious health and environmental hazard in addition to the operational problems. Therefore periodic analyses to detect and identify these contaminants at an early stage is becoming an acceptable industry practice. The following sections will address each type separately.

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Managing naturally occurring radioactive materials in production operations Annex IPage 4

I. NATURALLY OCCURRING RADIOACTIVE MATERIALS FROM PRODUCTION WATER

BACKGROUND

Naturally occurring radioactive materials NORM in formation water are soluble radionuclides, may precipitate, under certain operational environment, as low specific activity scale, known as LSA scales. These scales tend to be barium sulphate and strontium sulphate which co-precipitate with naturally occurring radium leached out of the reservoir rock; such scales emit alpha, beta and gamma radiation and this, together with the physical properties of the LSAS, can give rise to a number of problems if such scales or sludges have to be removed, handled or disposed.Once LSA scales are formed within the production system two main problems are presented: the scale will tend to foul valves and restrict the well fluid stream, and secondly, the levels of radiation on the outside of the flowline or vessel may be so high that the surrounding area may have to be designated as a restricted area and be cordoned off.Scale formation can be prevented with some success by the use of scale formation inhibiting chemicals. However, if the removal of LSA scale is necessary it can be difficult and expensive because LSA scales (unlike calcium carbonate scale) are insoluble in inorganic acids. Scale will either have to be removed (by hand or mechanically), or the scaled up equipment taken out of service and put into safe storage. Therefore safe systems of work and proper procedures which recognise the hazards, protect the workers from harmful exposure, minimise interference with the environment and ensure compliance with government and international regulations are essential.

1. ORIGIN AND FORMATION OF RADIOACTIVE SCALE

1.1 NATURALLY OCCURRING RADIOACTIVE ROCKS

The main radioelements found in the common sedimentary rocks include potassium, uranium and thorium and the highest concentrations are normally found in shales as indicated in Table 1.

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TABLE 1 – RADIOELEMENT CONCENTRATION IN SEDIMENTARY ROCKS

K-40(ppm)

U-238(ppm)

Th-232(ppm)

Sandstonesa) Orthoquartzites 1.7 0.45 1.7

b) Arkoses 1.5 5.0

Shalesa) Grey and green 2.9 3.2 13.1

b) Black 8-20

Limestones 0.4 2.2 1.1

Evaporites <0.1

The potassium content of shales is a reflection of their clay mineral, particularly illite content. The high uranium concentrations in black shales are probably due to their augmented organic content.Sandstones owe their potassium values to their K-felspar, K-mica and glauconite content.The uranium content of limestones is held largely within the crystal lattice of calcium carbonate where the uranium ions substitute for the calcium. Thorium, however, does not enter the carbonate lattice easily and, in consequence, thorium values tend to be low and held mainly in the clay and heavy mineral fractions. Uranium and thorium values in evaporites are, however, very low and restricted to the small detrital silicate mineral fraction.

1.2 RADIOACTIVE DEPOSITS

Generally it can be said that the radionuclide enrichment of the formation water occurs due to the concentration of uranium and thorium-bearing minerals within the source rock. Subsequent leaching by formation or injection water may result in radioactive deposits in the production train given suitable conditions. The injected seawater, being normally less saline than the formation water, may additionally dissolve radioactive salts from the minerals present in various geological strata. These deposit can take several forms:

SCALES

Natural formation water will undergo changes of temperature and pressure as it is co-produced with the oil and gas, and may under certain conditions deposit scale within the oil production system.Depending on variations in temperature, pressure, flow and geochemical conditions, these radioactive salts selectively precipitate in a non-reversible manner on the cement, or pipe around cased wells, liners, tubings, etc. This is significant from the radiological protection aspect since the co-precipitation effectively encapsulates the radium in a minerals shield, thereby ensuring almost complete self-absorption of the alpha particles emitted during the radioactive decay. Thus, a combination of radioactive leaching by either the natural formation water or the injected seawater together with the occurrence of injection water

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"breakthrough" may lead to deposits of mineral scale containing measurable quantities of natural radioactivity concentrated by this scaling process.

SAND AND SILT DEPOSITS

These are potentially a greater problem in topside equipment (e.g. production separators). This material can act as an absorbtive surface for radionuclides present in the production fluid. An exchange mechanism between cations can then give rise to radioactive sludges and deposits.Radon-222 gas is part of the decay chain of radium-226. In most cases where radioactive scale is produced radium-226 as well as some of its daughter nuclides including radon-222 may be found entrapped within the scale. Normally, radon-222 would be carried away with the normal gas. There are fears that where sludges are formed, the entrapped radon-222 gas may be given off in relatively large quantities, particularly when this sludge is being disturbed. Therefore precautions must be taken to protect the people working with such materials.

IRON (RUST) DEPOSITS

It has been noted that occasionally a matrix like iron oxide in oily-water separators has exhibited low levels of radiation. The mechanism is unclear, but there is some speculation that radium-226 could be locked into rust itself.

LEAD DEPOSITS

In some cases lead deposits occur which have high Pb 210 contents. They can occur with gas wells producing from carboniferous strata. Often they are characterised by high sodium chloride concentrations in the formation water. The deposits are usually found in well tubing and well heads.

2. ENVIRONMENTAL PROBLEMS

Radioactive scales and sludges or contaminated equipment may have to be removed at some time for storage or disposal. Since this could cause environmental problems strict precautions have to be taken to prevent the irradiation and contamination of people, animals, plants and other materials. The problems involved are:

2.1 Radioactive scales tend to be highly insoluble in acids. They contrast with most common nonactive shales (e.g. calcium carbonate) which are readily soluble in acids. Difficulties experienced in dissolving scale with inorganic acid should prompt to check for the presence of radioactivity.

2.2 LSA scales invariably emit alpha and beta particles and gamma rays. Their presence in production systems and equipment can give rise to occupational hygiene problems. A particular concern is with dust particles which can be released in cleaning operations. This dust can be trapped in the tissues of the lung and emit alpha particles which can cause longterm health problems. Where LSA scale is present in production trains or in

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items such as tubulars or wellheads, concern mainly centres on any effect that the gamma radiation could have on those working close by.

2.3 Radioactive scale on the insides of the tubing strings may interfere with the natural radioactive levels of the surrounding strata, causing anomalies in the readings from gamma ray logs. The observation of such gamma ray anomalies can be an early indicator of the presence of radioactive scales.

3. UNITS OF MEASUREMENT

The units used for Activity, Absorbed Dose and Dose Equivalent have recently changed following the introduction of SI units and are:

3.1 ACTIVITY

The activity of an amount of radioactive nuclide at a given time is the number of spontaneous nuclear transformations in the time unit. The SI unit of activity is the becquerel (Bq) equal to 1 nuclear transformation per second.

3.7 x 1010 Bq equals 1 Curie (Ci) exactly

37 M Bq equals 1mCi (millicurie)37 k Bq equals 1µCi (microcurie)The units generally used for measurement are Bq/g for solids and Bq/l for liquids and gases.

3.2 DOSE

A term denoting the quantity of radiation energy absorbed by a medium. Although the terms "dose" or "radiation dose" are often sued in a general sense, they should usually be qualified, for example as absorbed dose, dose equivalent, etc. The dose is still usually measured in pre SI units. Three pre SI units are used, viz:

3.2.1 the Roentgen which measures the radiation dose in air and is sometimes called the exposure dose;

3.2.2 the Rad which is a measure of the absorbed radiation dose, and

3.2.3 the Rem which is the unit of dose equivalent. For all practical purposes, it is assumed that doses measured in Roentgen are equal to doses measured in rads at the same position in the radiation field.

Only dosimeters for measuring neutrons are normally calibrated in rem units. The unit of dose equivalent takes into account the fact that some types of radiation, particularly alpha particles and neutrons, are much more efficient at killing or damaging cells per unit amount of absorbed dose. The rem dose is related to the rad dose by the following relationship:

Dose in rem = Dose in rad x QF(dose equivalent) (absorbed dose) (quality factor)

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The value of the quality factor can be as high as 20 for alpha particles and 10 for neutrons. For gamma and beta particles, it is 1. These units are large and for operational purposes measurements are made in mR, m rad or mrem, which are 1/1000 of the principal unit.Under SI units, the Roentgen does not have an equivalent. The unit of

absorbed dose replacing the rad is of the Gray or Joule kg1 and the unit of dose equivalent replacing the rem is the Sievert. These SI units are related in the same way as the rad and the rem, i.e.:

Dose in Sieverts (Sv) = Dose in Grays (Gy) x QFBy definition:

1 Gray = 100 rad1 Sievert = 100 remThe SI unit is thus even larger than the existing unit and measurements will be made in µGy or µSv (1/1,000,000th of the principal unit).

4. FIELD EQUIPMENT FOR RADIATION DETECTION

Generally there are two broad types of detectors available; contamination meters for measuring surface radiation such as alpha and beta, and the dose rate meters for measuring gamma radiation. There are also devices capable of measuring both beta and gamma radiation simultaneously.

4.1 CONTAMINATION METERS

These are very sensitive devices for measuring surface radiation. They indicate level of radiation in "counts per second" and should be able to measure alpha, alpha and beta, and beta radiation. The ability to measure these three ranges is necessary because if the LSA scale is damp, if there is moisture in the atmosphere or LSA scale is overlayed with calcium carbonate scale, then the alpha particles may be absorbed. However, by measuring alpha and beta emissions together the alpha emissions of the LSA scale may be inferred, i.e. as far as LSA scale is concerned alpha and beta particles are always emitted together. If an indication of LSA scale contamination is given by such a meter it must be confirmed by radiochemical analysis or gamma spectrometry.Contamination meters should be calibrated against a range of sources of known activity and of similar isotopic composition; the calibration chart then produced will enable, say, a

reading of five counts per second to be converted to 0.37 Bq/cm2 which would only be true for that particular meter. However, personnel trained in the use of such meters will soon become adept at interpreting readings correctly.Contamination meters, if treated with care, will give an early indication of a contamination problem, provided that the scale is not shielded.

4.2 RADIATION MONITORS OR DOSE RATE MATERS

These meters are reasonably robust and are used to measure radiation levels throughout industry. Generally they indicate measurements in Sievert/hr and measure gamma radiation. They are not as sensitive as contamination meters at measuring levels near background but are a very useful tool to establish whether or not LSA scale with higher levels of radiation is present inside pipelines, wellheads, vessels, etc. This is because the

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steel will stop the alpha and beta particles but allow a certain percentage of the gamma ray to pass; levels of radiation inside a steel pipeline or vessels may be in excess of two to three times those indicated outside, depending on the thickness of the steel.

4.3 AVAILABLE DEVICES

The available devices to measure gamma and beta radiation in the field equipment and facilities during operations and maintenance are:

• sodium iodide scintillation counters (SC);

• energy compensated geiger mueller (GM);

• thin window geiger mueller Pancake (PK).

4.4 GENERAL CONSIDERATIONS

Both types of meter are available from a number of manufacturers worldwide but there are some basic precautions which must be taken when either or both are used:

• the meters should be calibrated by a suitable laboratory and either, in the case of a contamination meter, a conversion chart supplied for that particular meter or, in the case of a dose rate meter, the meter adjusted to read as accurately as possible across the range;

• meters should be overhauled and calibrated at least once a year;

• if a meter is dropped or damaged it should be recalibrated;

• meters should not be abused and should be switched off and kept securely when not in use;

• personnel who use such meters should be trained in their operation, be able to interpret readings properly and be able to recognise when meters may not be working properly;

• indications of LSA scale should be confirmed by radiochemical analysis of gamma spectrometry so that a completely accurate record of the levels of radiation may be kept.

NOTE:

LSA scales with high levels of contamination, and therefore posing potentially high health risks of inhaled/ingested, may not register as such on dose rate meters and ideally, if the presence of LSA scale is suspected, both kinds of meter should be used together.

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5. RECOMMENDED LIMITS

5.1 DOSE LIMITS

The basic recommendations of the International Commission on Radiological Protection (ICPR) are laid down in its publications No. 26 and 30. However the "dose equivalent limit" recommended by ICPR is 50 mSv over one year according to the defined working conditions. Table 2 summarises these recommendations.

5.2 ACTIVITY LIMITS

When radioactive materials are handled, they should be classed as a radioactive substance when the specific activity level (the activity per unit of mass) is greater than 100 Bq/g. This limit only refers to the activity level of the material itself. This must be clearly distinguished from the limit that is used for decontamination purposes: the allowable

contamination level for alpha emitters on a surface is usually 2 Bqcm-2.Therefore, when either of these limits is exceeded, proper operation, handling and disposal are required.

6. OPERATIONAL PROCEDURES – DISPOSAL ASPECTS

6.1 SCALE HANDLING

When handling scale or scaled items, during such operations, as when pulling tubing, entering production separators or produced water skimmers, removal of Xmas trees, valves, meters and flowlines, etc. The following measures should be considered:

• contain contamination as near as possible to its site or production;

• limit the possibility of ingestion or inhalation;

• control and restrict direct exposure of workers;

• measure and record the levels of activity where scale is found;

• follow the recommended method of disposal.

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TABLE 2 – ACTIVITY AND RADIATION DOSE LIMITS

Involvement

Term

Classified workers

Working condition 'A' (1)Controlled area (2)

Non-classified workers

Working condition 'B' (1)Supervised area (2)

Public and workers with no involvement (special requirements for transportation)**

Dose limits (1) (2)for whole body

50 mSvYr-1 3/10 x 50mSv =

15 mSvYr-1

1/10 x 50 mSv =

5 mSvYr-1

for individual organs/tissues 500 mSvYr

-1 3/10 x 500 mSv =

150 mSvYr-1

1/10 x 500 mSv =

50 mSvYr-1

Derived levelsHourly limit for external expose of the whole body (2)

2000 µSv h-1

(recommended maximum for radiographers)

15 mSv

= 7.5 µSvh-1

2000 hours

5 mSv

= 2.5 µSvh-1

2000 hours"Annual limit of intake"* ALI of radioactive material (1)

Radium 226 by inhalation is

20 kBq Yr-1

Radium 226 by ingestion is

70 kBq Yr-1

3/10 ALI, e.g. for Radium 226 by inhalation 3/10 x 20 kBq

Yr-1

= 6 kBq Yr-1

1/10 ALI, e.g. for Radium 226 by inhalation 1/10 x 20 kBq

Yr-1

= 2 kBq Yr-1

Surface contamination level likely to result

ALI (2), e.g.

8 Bq cm-2

for Ra 226

3/10 ALI (2), e.g.

2.4 Bq cm-2

for RA 226

1/10 ALI (2), e.g.

0.8 Bq cm-2

for Ra 226

Airborne contamination+

ALI (2), e.g.

3 Bqm-3

for Ra 226

3/10 ALI (2),

e.g. 1 Bqm-3

for Ra 226

1/10 ALI,

e.g. 0.3 Bqm-3

for Ra 226

Radioactive substanceSpecific activity

100 Bq g-1

and any other substance having a lower activity concentration that cannot be disregarded for the radiological protection of persons at work (2).

0.4 Bqg-1

used for pollution control and disposal authorisations.

Precautions Use only classified workers or non classified workers working to a strictly controlled written system of work (dose limit 15 mSv per annum, i.e. 500 hrs per year at 30 µSv-hr); contain contamination.

ALARA***. Regular monitoring of affected areas. Contain surface contamination. Prevent airborne contamination.

ALARA*** and 'not significantly above background levels'. Controls on radioactive substances as pollutants.

Controlled disposal of radioactive substances. Occupational hygiene precautions to prevent inhalation and/or ingestion.

* Annual limit of intake (ALI): an ALI is the amount of radioactive material which if taken into the body would delivery a committed dose equivalent to the annual dose limit for either the whole body or individual tissues whichever is the more

restrictive. Each isotope has its own ALI, e.g. Radium 226 by inhalation is 20 BqYr-1

.

** Transport packages contain limit. On external surfaces of transport packages/containers the limit is 4 Bqcm-2

(3). 70 Bqg-

1 is limit used in transport regulations (3) (but check with national regulations for applicable limits).

*** ALARA: as low as is reasonably achievable.+ Airborne contamination: very different limits can apply to different isotopes,

e.g. 3 Bq m-3

– Ra 226; 0.01 Bq m-3

– natural thorium(1) Internal commission on radiological protection limits for intakes of radionuclides by workers, ICRP Publication No. 30, Part

2, Pergamon Press, Oxford, 1980.(2) EURATOM Directive of the Council about radiation protection of workers and the public.(3) International Atomic Energy Agency, Safety Series No. 6, Regulations for the Safe Transport of Radioactive Materials 1973,

Revised Edition (as amended), Vienna 1979.

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6.2 CONTAINMENT, DISPOSAL AND THE ENVIRONMENT

Disposal of LSA scale and sludges can be difficult and expensive, due to the occupational hygiene and environmental protection considerations discussed earlier. The following courses of action should be considered:

• containment;

• disposal.

6.2.1 CONTAINMENT

If tubulars are pulled and are found to be scaled, then provided that the scale is thin, hard, tenacious and smooth and offers little resistance to well fluid production, and provided that the tubing does not need to be reworked, then the scaled tubulars can be re-run back into the well. Similarly if a vessel is opened up for inspection and is found to contain LSA scales or sludges which are not interfering with production and the material does not have to be removed, then the vessel can be closed up again.

6.2.2 DISPOSAL

The decision logic for disposal is presented in Figure 1.Method of disposal include:

DISPOSAL TO THE SEA

Scales exhibiting levels of activity above background may be disposed of to the sea either from offshore installations or from onshore facilities with their own direct flushed outfall.Generally a maximum particle size (say 1 mm) could be specified together with a limit on the total activity (specific activity times weight) expressed in Gigabecquerels.Because particles of this size will obey Stokes Law, if this method is employed where there are reasonably strong tides and currents, there should be no detectable increase in the level of radioactivity in the sea or the surrounding seabed. In such instances, however, seabed surveys (much like those for oil-based mud cuttings) may be required.

DISPOSAL ON LAND

Listed below are methods of disposal on land:

• In specially dug pits, abandoned mines and oil wells: where such facilities are available, burial of scale in mines, pits or abandoned wells are possible methods of disposal.

• Storage in secure yards or warehouses: in many cases where it is considered too difficult or expensive to descale such items as tubulars, filter baskets, valves, etc., it may appear costeffective to put them into longterm secure storage. Such storage must only be used with the agreement of the relevant authorities.

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However, the following produced offshore, should be considered:

• the risks of exposing other workers to the hazards of LSA scale are increased (e.g. seamen, dockers, transport workers);

• if LSA scales are stored onshore, thought must be given to keeping such stores secure for generations in order to prevent workers from being exposed to risk in the future – the halflife of Radium 226 is 1620 years;

• if methods such as mixing 'concentrated' LSA scale with cement and then pumping the slurry into drums or down abandoned wells are used then again additional risks are incurred by the workers handling the scale.

6.3 SCALE INHIBITION AND SCALE DISSOLUTION

6.3.1 INHIBITION

Generally, it can be said that scale inhibition of Ba/SrSO4 using the correct programmes,

appropriate solutions and clean suitable equipment, will be successful. Scale inhibitor squeezes will usually be performed when it is known that barium is present in the formation water following the first indication of injection water breakthrough. An increasing sulphate ion count in the produced water is the usual indicator of the onset of breakthrough.

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Otherwise, the produced water must be monitored closely for other indications. Inhibitors can also be injected into the well fluid stream in the production train to help prevent scale formation in valves and production manifolds, etc.

6.3.2 DISSOLUTION

Scale dissolution, usually in the production train manifolds, has been attempted, most often using organic chemicals. Some of these organic chemicals show promise, but dissolution of the salts has still to be proven effective, due to their almost chemically inert nature.

7. PROCEDURE FOR A FIELD SURVEY

The initial survey for a NORM at a site is typically performed along the exterior of on-line intact equipment such as vessels, piping, compressors, and other production equipment. Of the three types of radiation present in NORM (alpha, beta and gamma), gamma rays alone can penetrate the steel and be detected outside the equipment. As discussed in the detection equipment section (section 4.3), the SC probe is used to identify areas of potential concern and the GM probe is used to quantify potential human doses.Both measurements can be made during the same survey using a meter that can support the two probes. The results of the survey should be documented and assigned one of the four categories (A, B, C, D) described in Table 3. Cut-offs of 2.5, 25 and 500 microSieverts/hour (uSv/hr) are used to define requirements needed to ensure a safe work environment9 such as limiting access, posting of signs, and other follow-up actions. (Note: 10 uSv/hr = 1 mR/hr). It is recommended that sites with NORM contamination be resurveyed every two years to identify changing conditions.

TABLE 3 – DETERMINATION OF AREA NORM CATEGORY

uSv/hr (GM) Category Definition Requirements

<2.5 A Public access area None

2.5-5 B Limited access area • Limit public access

• Document findings

• Inform maintenance

25-500 C Regulated area • Limit worker access

• Post with NORM sign

• Train workers

• Personal dosimetry

>500 D High radiation • Limit worker access

• Post with "high radiation" sign

• Train workers

• Personal dosimitry

• Work permit required

• Notify EA

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8. DECONTAMINATION

Any equipment, tools, or personal protective equipment (PPE) that has contacted NORM or LSAS contaminated surfaces needs to be evaluated to determine whether they have been contaminated. Similarly areas where NORM-related work has led to possible contamination also need to be evaluated.The decontamination decision logic is presented in Figure 2. Measurements are made using the GM probe and the PK probe (direct measurement or a wipe sample depending on the configuration of the surface). If both measurements are less than the criteria, the material is not considered to be NORM contaminated.For materials that do not meet the stated criteria, decontamination and repeat monitoring are one possible option. The other option is packaging for disposal.

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II.

RADIOACTIVE ELEMENTS IN NATURAL GAS

OCCURRENCE OF RADON

Natural gas contains small quantities of the gaseous radioactive nuclide Radon-222 formed from the decay of Radium-226, which is a daughter nuclide of naturally occurring Uranium-238. Radon enters natural gas in the earth by diffusion from a formation. Uranium minerals are often associated with carbonaceous deposits, therefore radon can be expected to occur in natural gas.Radon-222 has a half life of 3.8 days and produces upon decay a series of short and long lived daughter nuclides as shown in Figure (1). When propane is separated from natural gas, radon tends to be concentrated in the propane process stream since the boiling point of radon is close to that of propane. Consequently, it is typically enriched in propane by a factor of the order of 10.In natural gas condensate the long lived daughters of radon (particularly Lead-210 and Polonium-210) are generally present.

Figure (1) Decay scheme of the 238U

natural seriesNotes:

1) Halflives are indicated in years a, days d, minutes min, and seconds.

2) The nature of the radiation is indicated by α, β, and λ (only energetic λ radiations with high yield).

Recent reports of radon contaminated buildings through out the world, attest to the wide distribution of radon in the environment.Once formed by the radioactive decay of radium-226, radon is free to migrate as a gas or dissolve in water without being trapped or removed by chemical reaction. Migration through rocks and soil, radon is produced with natural gas at the wellhead. Table 1 shows

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that radon contamination of natural gas is a worldwide problem, and particularly high concentrations of radon are reported in the US and Canada.Table 1 - Radon concentrations in natural gas at the wellhead *Location of Well Radon concentration (pCi/L)

Borneo 1 to 3Canada

Alberta 10 to 205British Columbia 390 to 540Ontario 4 to 800

Germany 1 to 10The Netherlands 1 to 45Nigeria 1 to 3North Sea 2 to 4US

Colorado, New Mexico 1 to 160Texas, Kansas, Oklahoma 1 to 1,450Texas Panhandle 10 to 520Colorado 11 to 45California 1 to 100

*) From "Radon Concentration in Natural Gas at the Well, UN Scientific Committee on the Effects of Atomic Radiation; Sources and Effects of Ionizing Radiation, United Nations, New York City (1977).

When radon-contaminated produced gas is processed to remove the NGL's, much of the radon is removed also. Radon's boiling (or condensing) point is intermediate between the boiling points of ethane and propane. Upon subsequent processing, radon tends to accumulate further in the propylene distillation stream. Table 2 shows the boiling points of radon, the lighter NGL's, and propylene. As expected radon usually is recovered more completely in plants with high ethane recovery. The radon is concentrated in the lighter NGL's and is detected relatively easily with radiation survey meters.

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Table 2 - Boiling points at 760 mm Mercury°F

Methane -258.0Ethane -124.0Radon -79.2Propylene -53.9Propane -44.4Butane +31.1As long as it is contained and controlled within vessels, equipment, and piping, radon generally is not a health hazard to employees and the public. Even if radon-contaminated propane were released, the threat of fire or asphyxiation would far outweigh the hazard of a short-lived radiation exposure.

NORM IN NGL FACILITIES

Although entire natural-gas and NGL systems may be contaminated with NORM, some facilities will be contaminated to the extent that they present significant decontamination and disposal problems. Gasoline plants and other NGL facilities will be among the most highly contaminated areas in a system.During processing in a gasoline plant, the levels of external radiation from radon in propane 1 ft from a liquids pump may be as high as 25 milli-roentgens (mR)/hr. Radiation levels up to 6 mr/hr have been detected at outer surfaces of storage tanks containing fresh propane. Sludges in gasoline plants are often contaminated with several thousand picocuries of lead-210 per gram. Table 3 shows vessels and equipment in NGL service that may be significantly contaminated with NORM. Although NORM contamination will be general throughout an NGL facility, the contamination usually will be greatest in areas of high turbulence, such as in pumps and valves.Table 3 - Priority areas of concern for high radon and radon decay product

contamination

NGL facilitiesDe-ethanizersStillsFractionatorsProduct condensersFlash tanksPumps in liquid servicePiping in liquid serviceNGL storage tanksTruck terminalsFilter separatorsDessicantsWaste pits

PipelinesFiltersPig receivers

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Machine shopsIn-house Contract

When employees open equipment and vessels, precautions must be taken to prevent exposure to radioactive contamination. Maintenance procedures should include the use of respirators and good hygiene to prevent inhalation of radioactive dust. Grinding, if necessary, should be done wet to minimise dust.Occasionally, a plant or other facility that has been processing light hydrocarbons, particularly ethane and propane, is taken out of service and the facility sold or dismantled. Any equipment with internal surface deposits of NORM must receive special consideration when scrapped, sold, transferred, or otherwise disposed of, particularly when the facility is being released for unrestricted use. Analyses for lead-210 usually will be required to verify the extent of contamination and to determine if special handling is needed. Particularly care must be used to prevent employee exposure to NORM contamination.There are potential liabilities involved if contaminated equipment, vessels, and other parts of the facility are released or sold for unrestricted use without first being cleaned and tested to be essentially free of NORM contamination according to state and federal regulations.Much of the material wastes from a facility contaminated with NORM must be handled as low-level radioactive waste and disposed of accordingly. Contaminated wastes should be consolidated and separated from non-contaminated waste to keep radioactive waste volumes as low as possible. Consolidated contaminated wastes should be stored in a controlled-access area. The area should be surveyed with a radiation survey meter and, if required, should be posted.

THE INVESTIGATION LEVEL

Normally, the amount of radioactivity in the natural gas and its products is insufficient to cause health hazards during handling and subsequent use by consumers.However, it is recommended that the radon content of natural gas and Polonium-210 in the condensate of wells should be monitored prior to production. A record should also be kept of radon and polonium in gas and condensate from reservoirs which have been in production for a long period. The results of such measurements should be compared with a 'Derived Investigation Level'. A derived investigation level, as defined by the international Commission on Radiological Protection (ICRP), is a value of concentration of radioactive material. It is usually set in relation to a single measurement, which is the resulting radiation dose to humans sufficiently important to justify further investigation.It is important to recognise that an investigation level is not intended to be a limit. Should an investigation level be exceeded, this should be reported to the Central Offices EP Health, Safety and Environment Department (SIPM-EPO/6) who will contact the radiological specialists for advice. A close investigation of the (local) circumstances will be required. The investigation will often be no more than a recognition that the circumstances will not cause any hazard as the investigation level is based on a 'worst case' estimate. Below the investigation level, the information need not be further studied by experts.

CALCULATION OF THE INVESTIGATION LEVEL

Two types of radioactive exposure to humans resulting from radioactivity in natural gas or condensate can be identified:

a) During the use of the natural gas by consumers, e.g. heating and cooking.

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b) Relating to gas handling at gas processing stations.

In both cases, a derived investigation level will be specified.

NATURAL GAS AND LPG FOR DOMESTIC CONSUMPTION

When natural gas or LPG is burned in domestic appliances (cooking and heating) radon will be emitted into the atmosphere and contribute to the radiation level already naturally present. Radon (and its daughter nuclides which are formed by decay) become attached to aerosol particles and may subsequently be inhaled.To calculate the derived investigation level for radon in raw natural gas, the following 'worst case' conditions are assumed:

Minimal ventilation and maximal invented appliances of LPG in which radon is enriched.

The combustion products will all contribute to the radon concentration in indoor air.

The maximum permissible yearly dose to members of the public is 5 mSv/a (milliSievert per year, a unit for the ionising radiation dose to human beings). As a base for the derived investigation level, one twentieth of this dose equivalent is taken, i.e. 0.25 mSv/a. This dose equivalent is not exceeded when the concentration in the natural gas is below 2 kBq/m3 (50 pCi/dm3). For comparison, the average yearly dose from the natural background and medical radiation is around 3 mSv/a. This level can be considered as the derived investigation level for radon in raw natural gas taking into account the use of recoverable LPG when converted into fuel gas.For use of natural gas as an industrial fuel gas, the same investigation level should be used, provided that the investigation level for surface contamination is not exceeded.

CONTAMINATION OF GAS PROCESSING EQUIPMENT

Inner parts of gas processing equipment may be contaminated with the long lived daughter products of Radon-222 as a result of deposition of the solid daughters (particularly the long lived Pb-210 and Po-210) at places where the stream is dispersed over a large surface or where high turbulence occurs. An additional effect is the enrichment in the propane stream (see 3.8.1) which causes an increased chance of contamination in the propane stream equipment.Similarly, Polonium-210 present in the condensate may be deposited in pumps, distillation columns, heat exchangers, etc.The chance of contamination above a certain level is related to the initial concentration of radon or polonium in natural gas or natural gas condensate. However, possible enrichment and the throughput of gas or condensate are also important factors.The long lived daughters of radon (e.g. Polonium-210) mainly emit alpha radiation which cannot penetrate steel walls of equipment. Only the short lived Bismuth-214 may be detectable at the outside of the equipment. In view of the short half-life, however, the external radiation level will always be minimal and will disappear after shut-down of the installation.

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Thus, radiation hazards, if present, may only occur when opening equipment, by inhalation or ingestion of the contamination. Before workers enter equipment which has been exposed to condensate containing polonium or propane containing radon, it may be advisable to monitor the inner surfaces to avoid the risk of contamination of the personnel involved. For a derived investigation on surface contamination of equipment, 4 kBq/m3 (10 pCi/cm2) should be used.Since the mechanism for deposition of solid daughters of radon (e.g. Polonium-210) cannot be quantitatively described, it is not possible to calculate investigation levels for liquid concentration of radon or Polonium-210 resulting in contamination. However, from experience, contamination of inner surfaces of equipment is unlikely when the level of Polonium-210 in natural gas condensate is below 20 kBq/m3 (0.5 pCi/cm3).

MONITORING

Radon-222 in natural gas can be detected using an ionisation chamber. Radon concentration determination is usually carried out as one of the routine tests during production testing of new gas reservoirs.Several methods for determination of Polonium-210 in natural gas condensate are available. One of the accurate methods consists of extraction of Po-210 from the condensate and acid destruction followed by plating Po-210 on a silver disc. The alpha activity on the silver surface is determined using, for example, a surface barrier detector.For detection of contamination of inner surfaces of equipment, a simple technique developed by KSLA of applying a film sensitive to alpha radiation is available.

SUGGESTED PROGRAMME FOR THE CONTROL OF NORM

The following are suggestions for use in establishing a programme for the control of NORM contamination.1) Determine whether there is a NORM contamination problem.

2) Determine areas of potential NORM exposure and contamination.

a) Make gamma radiation surveys of facilities and equipment.

b) Make wipe tests on accessible interior surfaces of selected equipment and vessels, especially any in NGL service.

c) Obtain samples of sludges and scale and analyse for radium and lead210.

d) Obtain samples of other waste materials, such as dessicants and filters.

e) Analyse produced water and waste pond water for radium.

3) Establish programmes to ensure personnel safety, products quality, customer satisfaction, and protection of the environment.

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a) Establish policy on periodic surveys, inspection and maintenance procedures, product controls, and record keeping.

b) Provide safetymanual material that informs employees and details required procedures, particularly for maintenance personnel.

c) Recommend a management and audit system.

d) Develop plans and procedures for the disposal of contaminated waste materials, equipment, and facilities.

REFERENCES

1. Low specific activity scale: origin, treatment and disposalE&P Forum Report No. 6.6/127, 1988

2. E.C. Thayer and L.M. RacioppiNaturally occurring radioactive materials: the next stepSPE 23500, 1991

3. P.R. Gray "NORM contamination in Petroleum Industry" JPT Jan. 1993.4. G.E. Jackson

Formation and inhibition of scale in offshore oil productive systemsOffshore Radioactivity Seminar, OYEZ London, 1983

5. K.S. JohnsonWater scaling problems in the oil production industryin Chemicals in the Oil Industry, Ed. P.H. Ogden, 1983

6. UKOOA Reference Manual on naturally occurring radioactive substances on offshore installationsUKOOA, London, 1985

7. W.A. Kolb and M. WojcikEnhanced radioactivity due to natural oil and gas production and related radiological problemsScience of the Total Environment 45, 7784, 1985

8. A.L. SmithRadioactive scale formationOTC 5081, Offshore Technology Conference, Houston, 1985

9. P.R. Gray "Radioactive materials could pose problems for the gas industry" Oil & Gas J. (June 25, 1990) 45-48.

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10. J. Summerlin Jr. and H.M. Prichard "Radiological Health Implications of Lead-210 and Polonium-210 Accumulations in LPG Refineries" J. American Industrial Hygiene Assn. (1985) 46, No. 4, 202-05.

11. E&P Form Report no. 6.6/127, 1988. Low Specific Activity Scale.12. E.C. Tayler & C.M. Raciopi NORM; "The Next Step", SPE 23500, 1991.

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RADIOLOGICAL UNITS – SI CONVERSIONSCONVERSION TABLE

ACTIVITY UNITS

1pCi = 37mBq 1mBq = 0.027pCi = 27fCi1nCi = 37 Bq 1 Bq = 27pCi1µCi - 37KBq 1KBq = 27 nCi1mCi = 37MBq 1MBq = 27µCi1 Ci = 37GBq (37E+09Bq) 1GBq = 27mCi1KCi = 37TBq 1TBq = 27Ci

CURIES TO BECQUERELS

1 pCi 1 nCi 1 µCi 1m Ci 1 Ci37 mBq 37 Bq 37 KBq 37 MBq 37 GBq

BECQUERELS TO CURIES

1 Bq 1 kBq 1 MBq 1 GBq 1 TBq27 pCi 27 nCi 27 µCi 27 mCi 27 Ci

ABSORBED DOSE UNITS

1µrad = 0.01µGy 1µGy = 100µrad1mrad = 0.01mGy 1mGy = 100mrad1 rad = 0.01 Gy = 10mGy 1 Gy = 100 rad1Krad = 10 Gy 10 KGy = 0.1Mrad1Mrad = 10 KGy 1MGy = 100 Mrad

DOSE EQUIVALENT UNITS

1µrem = 0.01µSv 1µSv = 100 µrem1mrem = 0.01mSv=10Mv 1mSv = 100 mrem1 rem = 0.01 Sv=10mSv 1 Sv = 100 rem1Krem = 10 Sv 1KSv = 0.1Mrem1Mrem = 10 KSv 1MSv = 0.1Grem(H)µrem mrem mrem mrem mrem

1 1 10 10 11 10 100 1 10

(H)µSv µSv µSv mSv mSv

PREFIXES

k kilo - thousand (103) m milli - thousandth (10

-3)

M mega - million (106) µ micro - millionth (10

-6)

G giga - thousand million (109) n nano - thousand-millionth (10

-9)

T tera - million million (1012

) p pico - million-millionth (10-12

)

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GLOSSARYActivity The quantity of a radionuclide described by the number of nuclear

transformations occurring per unit time (see becquerel and curie).

ALARA As low as is reasonably achievable.

Alpha particle (α) A charged particle emitted from the nucleus of an atom having a mass and charge equal in magnitude to that of a helium nucleus, i.e. two protons and two neutrons.

Becquerel The SI unit of activity. One Becquerel (symbol Bq) equals one nuclear transformation per second.

Beta particle (β) Charged particle emitted from the nucleus of an atom, with a mass and charge equal in magnitude to that of the electron.

Coelestobarite Ba/Sr(Ra)SO4 solid solution of RaSO

4 in Ba/SrSO

4.

Contamination (radioactive)

Radioactive material in any place where it is not desired particularly where its presence may be harmful. The harm may be in inhaling or ingesting the radioactive material which may cause internal radiation dose.

Controlled area A defined area in which the occupational exposure of personnel (to radiation) is under the supervision of the Safety/Radiation Adviser and the dose rate is above 7.5 µSv/hr.

Counter (GeigerMuller)

A glass or metal envelope containing a gas and two electrodes. Ionising radiation causes discharges, which are registered as electric pulses in a counter. The number of pulses is related to the dose.

Counter (Proportional) A similar device as a GeigerMuller counting tube; the intensity of the electric pulses produced is proportional to the energy of the primary ionising particles.

Counter (Scintillation) A device containing material that emits light flashes when exposed to ionising radiation. The flashes are converted into electric pulses by a photomultiplier.

Curie The preSI unit of activity. One curie (abbreviated Ci) equals 3.7 x 10

10 nuclear transformations per second, i.e. it equals 37

gigabecquerel.

Decay Disintegration of the nucleus of an unstable nuclide by spontaneous emission of charged particles and/or photons. It causes the decrease in activity or radioactive substances.

Detector (Radiation) Any device for converting radiant energy to a form more suitable for observation. An instrument used to determine the presence, and sometimes the amount, of radiation.

Dose A general term denoting the quantity of radiation or energy absorbed. For special purposes it must be appropriately qualified. If unqualified, it refers to absorbed dose.

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Collective effective dose

The quantity obtained by multiplying the average effective dose equivalent by the numbers of persons exposed to a given source of radiation. Expressed in mansievert. Frequently abbreviated to collective dose.

Cumulative radiation dose (radiation)

The total dose resulting from repeated exposures to dose.

Dose equivalent (symbol H)

A quantity used in radiation protection. It expressed all radiation on a common scale for calculating the effective absorbed dose such that biological effects can be compared. It is defined as the product of the absorbed dose and the quality factor (see Quality factor and Sievert).

Effective dose equivalent

The quantity obtained by multiplying the dose equivalents to various tissues and organs by the risk weighting factor appropriate to each and summing the product. This procedure makes it possible to compare this number with a wholebody dose equivalent.

Maximum permissible dose equivalent (MPD)

The greatest dose equivalent that a person or specified part thereof shall be allowed to receive in a given period of time. This quantity has been rejected in ICRP 26.

Dose rate Absorbed dose delivered per unit of time.

Dosimeter Instrument to detect ad measure a dose received. For example, a pencilsize ionisation chamber with a selfreading electrometer, used for personnel monitoring.

Exposure A measure of the ionisation produced in air by X or gamma radiation (see Roentgen).

Gamma ray (γ) Shortwave length electromagnetic radiation of nuclear origin (range of energy from 10 KeV to 9 MeV) emitted from the nucleus.

Gray (symbol Gy) The unit of absorbed dose. One gray equals one joule per kilogramme.

Halflife (radioactive) (symbol t

1/2)

Time required for a radioactive substance to lose half of its activity by decay. Each radionuclide has a unique halflife.

IAEA International Atomic Energy Authority.

ICRP International Commission on Radiological Protection.

Ionising radiation Radiation that produces ionisation in matter. Examples are alpha particles, beta particles, gamma rays, X rays and neutrons.

Irradiation Exposure to radiation.

Isotopes Nuclides having the same number of protons in their nuclei, and hence the same atomic number, but differing in the number of neutrons, and therefore in the mass number. Almost identical chemical properties exist between isotopes of a particular element. The term should not be used as a anonym for nuclide.

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Joule The unit for work and energy, equal to one Newton expended along a distance of one metre (IJ = 1N x 1m).

Monitoring Periodic or continuous determination of the amount of ionising radiation or radioactive contamination present.

Nuclide A species of atom characterised by the number of protons and neutrons, and the energy content.

Rad The preSI unit of absorbed dose; equal to 0.01 J/kg (see Gray).

Radiation The emission and propagation of energy through space or through a material medium in the form of waves; for instance, the emission and propagation of electromagnetic waves. The term radiation or radiant energy, when unqualified, usually refers to electromagnetic radiation. Such radiation commonly is classified, according to frequency, as hertzian, infrared visible (light), ultraviolet, X ray, and gamma ray (see Photon).

Background Radiation arising from radioactive material other than the one directly under consideration. Background radiation due to cosmic rays and natural radioactivity is always present. There may also be background radiation due to the presence of radioactive substances in other parts of the building, in the building material itself, etc.

External Radiation from a source outside the human body.

Internal Radiation from a source within the body (as a result of incorporation and deposition of radionuclides in body tissues).

Radioactivity The property of certain nuclides of spontaneously emitting particles or electromagnetic radiation.

Radionuclide An unstable nuclide that emits ionising radiation.

Radon In the context of this report Radon is taken to mean either Radon 222 or Radon 220 – radioactive gases produced by decay of Ra 226 or Ra 224.

Rem The preSI unit of dose equivalent; equal to 0.01 J/kg (see Sievert).

Risk factor In connection with ionising radiation, the probability of cancer and leukaemia or genetic damage per unit dose equivalent. Usually refers to fatal malignant diseases and serious genetic damage. Expressed in Sv.

Roentgen (R) The preSI unit of exposure. One Roentgen is the dose given by a radiation field that produces ionisation, due to secondary electrons, of one electrostatic unit of charge per cm3 (NTP) of air. It is equal to 2.58 x 106 coulomb per kilogramme of air.

Sealed substance (or source)

A radioactive substance sealed in an impervious container which has sufficient mechanical strength to prevent contact with and dispersion of the radioactive substance under the conditions of use and wear for which it was designed.

Shield A body of material used to prevent or reduce the passage of particles or radiation.

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SI Abbreviation of "Système International d'Unites", the International System of Units, recommended for general use.

Sievert (symbol Sv) The unit of (effective) dose equivalent. The sievert has the dimensions of joule per kilogramme. The dose equivalent in sieverts is numerically equal to the absorbed dose in grays multiplied by the quality factor (see Gray and Quality factor).

Specific activity Total activity of a given nuclide per unit mass of the specific material.

Tracer (isotopic) The isotope or nonnatural mixture of isotopes of an element which may be incorporated into a sample to permit observation of the course of that element, alone or in combination, through a chemical, biological, or physical process.

Tritium The hydrogen isotope with one proton and two neutrons in the nucleus. (Symbol 3 H or H3, sometimes T).

X rays Electromagnetic radiation of which the wave lengths are shorter than those of visible light. They are usually produced by bombarding a metallic target with fast electrons in a high vacuum, as occurs in an X ray machine.

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Documents

Senv Guidelines for Management of Norm (1)