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Oil and Gas Production Wastes
TENORM
The geologic formations that contain oil and gas deposits also contain naturally-occurring radionuclides, which are referred to as "NORM" (Naturally-Occurring Radioactive Materials):
- uranium (and its decay products)
- thorium (and decay products)
- radium (and decay products)
- lead-210
Geologists have recognized their presence since the early 1930s and use it as a method for finding deposits (Ma87).
Much of the petroleum in the earth's crust was created at the site of ancients seas by the decay of sea life. As a result, petroleum deposits often occur in aquifers containing brine (salt water). Radionuclides, along with other minerals that are dissolved in the brine, precipitate (separate and settle) out forming various wastes at the surface:
- mineral scales inside pipes
- sludges
- contaminated equipment or components
- produced waters.
Because the extraction process concentrates the naturally occurring radionuclides and exposes them to the surface environment and human contact, these wastes are classified as TENORM.
On this page:
- How are drilling wastes produced?
- How much radiation is in the wastes?
- Waste Types and Amounts
- Disposal and Reuse: Past Practices
- Disposal and Reuse: Current Practices
- Exposure Risks
- What is being done?
- Resources
How are drilling wastes produced?
The briney solution contained in reservoirs of oil and gas is known as "formation water." During drilling, a mixture of oil, gas, and formation water is pumped to the surface. The water is separated from the oil and gas into tanks or pits, where it is referred to as "produced water." As the oil and gas in the reservoir are removed, more of what is pumped to the surface is formation water. Consequently, declining oil fields generate more produced water.
While uranium and thorium are are not soluble in water, their radioactive decay product, radium, and some of its decay products are somewhat soluble. Radium and its decay products may dissolve in the brine. They may remain in solution or settle out to form sludges, which accumulate in tanks and pits, or mineral scales, which form inside pipes and drilling equipment.
How much radiation is in the wastes?
Because radium levels in the soil and rocks vary greatly, so do their concentrations in scales and sludges. Radiation levels may vary from background soil levels to as high as several hundred nanoCuries per gram. The variation depends on several factors:
- concentration and identity of the radionuclides
- chemistry of the geologic formation
- characteristics of the production process (McA88).
The table below shows the range of activities in these wastes:
| Wastes | Radiation Level [pCi/g] | ||
|---|---|---|---|
| low | average | high | |
| Produced Water [pCi/l] | 0.1 | NA |
9,000 |
| Pipe/Tank Scale [pCi/g] | <0.25 | <200 | >100,000 |
The Radiation in TENORM Summary Table provides a range of reported concentrations, and average concentration measurements of NORM associated with various waste types and materials.
Waste Types and Amounts
Each year the petroleum industry generates around 150,000 cubic meters (260,000 metric tons) of waste including produced water, scales, sludges, and contaminated equipment. The amount produced at any one oil reserve varies and depends on several factors:
- geological location
- formation conditions
- type of production operation
- age of the production well.
An estimated 30 percent of domestic oil and gas wells produce some TENORM (McA88). In surveys of production wells in 13 states, the percent reporting high concentrations of radionuclides in the wells ranged from 90 percent in Mississippi to none or only a few in Colorado, South Dakota, and Wyoming (McA88). However, 20 to 100 percent of the facilities in every state reported some TENORM in heater/treaters.
Produced Waters
The radioactivity levels in produced waters are generally low, but the volumes are large. The ratio of produced water to oil is approximately 10 barrels of produced water per barrel of oil. According to the American Petroleum Institute (API), more than 18 billion barrels of waste fluids from oil and gas production are generated annually in the United States.
Produced waters contain levels of radium and its decay products that are concentrated, but the concentrations vary from site to site. In general, produced waters are re-injected into deep wells or are discharged into non-potable coastal waters.
Scale
Scale is composed primarily of insoluble barium, calcium, and strontium compounds that precipitate from the produced water due to changes in temperature and pressure. Radium is chemically similar to these elements and as a result is incorporated into the scales. Concentrations of Radium-226 (Ra-226) are generally higher than those of Ra-228.
Scales are normally found on the inside of piping and tubing. The API found that the highest concentrations of radioactivity are in the scale in wellhead piping and in production piping near the wellhead. Concentrations were as high as tens of thousands of picocuries per gram. However, the largest volumes of scale occur in three areas:
- water lines associated with separators, (separate gas from the oil and water)
- heater treaters (divide the oil and water phases)
- gas dehydrators, where scale deposits as thick as four inches may accumulate .
Chemical scale inhibitors may be applied to the piping complexes to prevent scales from slowing the oil extraction process. If the scales contain TENORM, the radiation will remain in solution and eventually be passed on to the produced waters.
Approximately 100 tons of scale per oil well are generated annually in the United States. As the oil in a reservoir dwindles and more water is pumped out with the oil, the amount of scale increases. In some cases brine is introduced into the formation to enhance recovery; this also increases scale formation.
The average radium concentration in scale has been estimated to be 480 pCi/g. It can be much higher (as high as 400,000 pCi/g) or lower depending on regional geology.
Sludge
Sludge is composed of dissolved solids which precipitate from produced water as its temperature and pressure change. Sludge generally consists of oily, loose material often containing silica compounds, but may also contain large amounts of barium. Dried sludge, with a low oil content, looks and feels similar to soil.
Oil production processes generate an estimated 230,000 MT or five million ft3 (141 cubic meters) of TENORM sludge each year. API has determined that most sludge settles out of the production stream and remains in the oil stock and water storage tanks.
Like contaminated scale, sludge contains more Ra-226 than Ra-228. The average concentration of radium in sludges is estimated to be 75 pCi/g. This may vary considerably from site to site. Although the concentration of radiation is lower in sludges than in scales, sludges are more soluble and therefore more readily released to the environment. As a result they pose a higher risk of exposure.
The concentration of lead-210 (Pb-210) is usually relatively low in hard scales but may be more than 27,000 pCi/g in lead deposits and sludge.
Contaminated Equipment
Oil drilling rig.(click for larger image.)
TENORM contamination levels in equipment varied widely among types of equipment and geographic region. The geographic areas with the highest equipment readings were northern Texas and the gulf coast crescent from southern Louisiana and Mississippi to the Florida panhandle. Very low levels of TENORM were found in California, Utah, Wyoming, Colorado, and northern Kansas.
According to an API industry-wide survey, approximately 64 percent of the gas producing equipment and 57 percent of the oil production equipment showed radioactivity at or near background levels. TENORM radioactivity levels tend to be highest in water handling equipment. Average exposure levels for this equipment were between 30 to 40 micro Roentgens per hour (μR/hr), which is about 5 times background. Gas processing equipment with the highest levels include the reflux pumps, propane pumps and tanks, other pumps, and product lines. Average radiation levels for this equipment as between 30 to 70 μR/hr. Exposures from some oil production and gas processing equipment exceeded 1 mR/hr.
Gas plant processing equipment is generally contaminated on the surface by lead-210 (Pb-210). However, TENORM may also accumulate in gas plant equipment from radon (Rn-222) gas decay. Radon gas is highly mobile. It originates in underground formations and dissolves in the organic petroleum areas of the gas plant. It concentrates mainly in the more volatile propane and ethane fractions of the gas.
Gas plant scales differ from oil production scales, typically consisting of radon decay products which accumulate on the interior surfaces of plant equipment. Radon itself decays quickly, (its half-life is 3.8 days). As a result, the only radionuclides that affect disposal are the radon decay products polonium-210 (Po-210) and lead-210. Polonium-210 is an alpha emitter with a half-life of 140 days. Pb-210 is a weak beta and gamma emitter with a half-life of 22 years.
Disposal and Reuse: Past Practices
Recycling of Metals
Before the accumulation of TENORM in oil production equipment was recognized, contaminated materials were occasionally recycled for use in making steel products:
- load-supporting beams in house construction
- plumbing for culinary water
- fencing materials
- awning supports
- practice welding material in class rooms.
Disposal of Wastes
When sludge fouling in water and oil storage tanks became a problem, the tanks were drained and the sludge disposed of in waste pits:
-
Burn pits
Earthen pits were previously used for temporary storage an periodic burning of non-hazardous oil field wastes collected from tanks and other equipment. -
Brine pits
Lined and/or earthen pits were previously used for storing produced water and other nonhazardous oil field wastes, hydrocarbon storage brine, or mining wastes. In this case, TENORM in the water will concentrate in the bottom sludges or residual salts of the ponds. Thus, the pond sediments pose a potential radiological health risk. The radionuclides in these soils have been reported to be in the range from 270 to 1100 pCi/g.
Disposal and Reuse: Current Practices
Recycling of Metals
Now that the petroleum industry is aware of the potential for contamination, they take a number of precautions before recycling:
- Loads of scrap metal are surveyed for hidden radioactive sources and TENORM.
- Piping and equipment are cleaned before release for recycling at smelters.
- Pollution control devices, such as filters and bubblers, are installed in smelter stacks to reduce airborne radiation releases.
Although much of the NORM-contaminated equipment is presently stored in controlled areas, some companies are now cleaning the equipment and proposing to store it at designated disposal sites.
Waste disposal
The average concentration of the radium in the oil and gas wastes at offsite and onsite disposal facilities is approximately 120 pCi/g. EPA has issued non-mandatory guidelines identifying radium concentrations limits for disposal at landfills:
-
3- 50 pCi/g
disposal in sanitary landfills, with limited access and no future development of the site -
50-2,000 pCi/g
disposal in TENORM or Low-Level Radioactive Waste facilities - Greater than 2,000 pCi/g
disposal according to Atomic Energy Act regulations.
Sludges containing elevated TENORM are now dewatered and held in storage tanks for later disposal.
Produced waters are now generally reinjected into deep wells or, in the case of offshore production facilities, are discharged into non-potable coastal waters. No added radiological risks appear to be associated with this disposal method as long as the radioactive material carried by the produced water is returned in the same or lower concentration to the formations from which it was derived. As of 1992 there are 166,000 injection wells in 31 states.
Pipes contaminated with scale are cleaned at pipe yards either by sandblasting them with high pressure water or by scraping out the scale with a rotating drill bit. The removed scale is then placed in drums and stored for later disposal.
Contaminated equipment may either be cleaned and reused by the petroleum industry; disposed; or, if radiation levels are sufficiently reduced, sold for recycle. If equipment cannot be further decontaminated to acceptable levels, it is sent to a landfill licensed to accept NORM materials.
In some cases contaminated steel may be reprocessed via smelting. During the smelting process molten steel separates from the NORM which vaporizes and is released as a gas. If the steel mill has pollution control equipment, most of the NORM is trapped in the baghouses and scrubbers. A typical smelting operation is capable of capturing 99 percent of the particulate releases.
Exposure Risks
TENORM contamination in oil production waste came to the attention of industry and government in 1986 when, during routine well work in Mississippi, barium sulfate scale in tubing was found to contain elevated levels of levels of radium-226, and thorium-232.
Because of concerns that some pipes may have contaminated the surrounding environment, radiological surveys were conducted by EPA's Eastern Environmental Radiation Facility. These surveys showed that some equipment and disposal locations exhibited external radiation levels above 2 mR/hr and radium-226 soil contamination above 1,000 pCi/g. Some contamination had also washed into a nearby pond and drainage ditch at one site, as well as into an agricultural field with subsequent uptake of radium by vegetation.
Because TENORM contaminated wastes in oil and gas production operations were not properly recognized in the past, disposal of these wastes may have resulted in environmental contamination in and around production and disposal facilities. Surface disposal of radioactive sludge/scale, and produced water (as practiced in the past) may lead to ground and surface water contamination.
Those at risk include:
- oil/radiation waste disposal workers
- nearby residents/office workers.
Oil/Radiation Waste Disposal Workers
Disposal workers include those who work directly on top of uncovered waste sites. Potential risks assessed for these workers include exposures due to direct gamma radiation and radioactive dust inhalation. In addition, they may inhale radon gas which is released during drilling and produced by the decay of radium, raising their risk of lung cancer. Workers following safety guidance will reduce their total on-site radiation exposure.
Nearby Residents/Office Workers
Risks evaluated for members of the public working or residing within 100 meters of a disposal site are similar to those of disposal workers. They include: direct gamma radiation, inhalation of contaminated dust, inhalation of downwind radon, ingestion of contaminated well water, ingestion of food contaminated by well water, and ingestion of food contaminated by dust deposition.
Risks analyzed for the general population within a 50 mile radius of the disposal site include exposures from the downwind transport of re-suspended particulates and radon, and exposures arising from ingestion of river water contaminated via the groundwater pathway and surface runoff. Downwind exposures include inhalation of re-suspended particulates, ingestion of food contaminated by deposition of re-suspended particulates, and inhalation of radon gas.
Individuals working inside an office building inadvertently constructed on an abandoned NORM waste pile also face the threat of radiation exposure. Potential risks assessed for the onsite individual include exposures from direct gamma radiation, dust inhalation, and indoor radon inhalation.
What is Being Done About These Wastes
The problem of TENORM contamination is now known to be widespread, occurring in oil and gas production facilities throughout the world. It has become a subject of attention in the United States and in other countries. In response to this concern, facilities in the U.S. and Europe have been characterizing the nature and extent of TENORM in oil and gas pipe scale, evaluating the potential for exposure to workers and the public, and developing methods for properly managing these low specific-activity wastes.
Both the oil and gas industry and state regulatory agencies are currently examining and regulating TENORM in oil and gas production facilities. The API has sponsored studies to characterize accumulations of TENORM in oil field equipment and to evaluate methods for its disposal. The API has also formed an Ad Hoc Committee on Low Specific-Activity (LSA) Scale and has prepared a draft measurement protocol for identifying producing areas where NORM scale is known to exist. The Part N Subcommittee of the Conference of Radiation Control Program Directors has been working since 1983 to develop model state regulations (Part N of Suggested State Regulations for Control of Radiation) for the control of NORM. While these regulations are intended to apply generally to all NORM-containing materials, several parts would apply specifically to oil and gas industry pipe scale.
Many states with oil and gas production facilities are currently creating their own NORM regulations. For example, the State of Louisiana has regulations for NORM in scales and sludges from oil and gas production that differ from the Part N model regulations, where the State of Texas has NORM regulations similar to Part N regulations.
Resources
Sector Notebook Project – Oil and Gas Extraction (PDF) (41pp, 444Kb [about pdf format] )
2000. U.S. Environmental Protection Agency, Office of Enforcement and Compliance Assurance
This document provides a description of the oil and gas extraction process, how to comply with EPA’s health and the environmental laws and techniques for pollution prevention.
Who is Protecting you? U.S. Environmental Protection Agency
This site lists a number of federal and state agencies responsible for regulating radioactive materials and workers safety.
Health Effects U.S. Environmental Protection Agency
Site provides information on the health effects associated with a range of radiation exposures.
Potential Health Hazards Associated with Handling Pipe Used in Oil and Gas Production 26 January 1989. OSHA Hazard Information Bulletins. U.S. Department of Labor, Occupational Safety and Health Administration
This document warns workers of possible inhalation or ingestion of radioactive material in cutting and welding oil and gas pipes.
The American Petroleum Institute
Trade association that represents all aspects of America’s oil and natural gas industry.
