TENORM: Oil and Gas Production Wastes
In recent years, oil and gas producers have employed new methods that combine horizontal drilling with enhanced stimulation. These new methods, known as "frackingfrackingHydraulic fracturing, also referred to as "fracking," is the process of drilling into host formations (shales and tight sandstones) and injecting fluids and sand under pressures great enough to fracture the rock formations to allow the extraction of oil and gas.," have changed the profile of oil and gas wastes - both in terms of radioactivityradioactivityThe emission of ionizing radiation released by a source in a given time period. The units used to measure radioactivity are becquerel (Bq) and curie (Ci). and volumes produced. The geologic formations that contain oil and gas deposits also contain naturally-occurring radionuclides, which are referred to as Naturally Occurring Radioactive Materials (NORM):
- Uranium and its decay products.
- Thorium and decay products.
- Radium and decay products.
Much of the petroleum and natural gas developed in the U.S. was created in the earth's crust at the site of ancient seas by the decay of sea life. As a result, these shale, petroleum and gas deposits often occur in aquifers containing brine (salt water). Radionuclides, along with other minerals that are dissolved in the brine, separate and settle out, forming various wastes at the surface:
- Mineral scales inside pipes.
- 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 Technologically Enhanced Naturally Occurring Radioactive Material (TENORM).
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 formation are removed, much of what is pumped to the surface is formation water. Consequently, declining oil and gas fields generate more produced water.
While uranium and thorium are not soluble in water, their radioactive decay productsdecay productsThe atoms formed and the energy and particles emitted as radioactive material decays to reach a stable form. such as radium may dissolve in the brine. They may remain in solution or settle out to form sludges that accumulate in tanks and pits, or form mineral scales inside pipes and drilling equipment.
How much radioactivity is in the wastes?
Radium levels in the soil and rocks vary greatly, as do their concentrations in scales and sludges. Radiation levels may vary from background soil levels more than 4 becquerels per gram (Bq/g), or several hundred picocuries per gram (pCi/g). The variation depends on several factors:
- Concentration and identity of the radionuclides.
- Chemistry of the geologic formation.
- Characteristics of the production process.
Waste Types and Amounts
For conventional drilling, one industry study published in 2000 (with data from the 1990s)1 showed that the petroleum industry generated around 150,000 cubic meters (260,000 metric tons) of waste per year, including produced water, scales, sludges and contaminated equipment. The amount produced at any one oil play varies and depends on several factors:
- Geological location.
- Formation conditions.
- Type of production operation.
- Age of the production well.
The volume of wastes from unconventional drilling can be much higher, since the length of the wells through the host formation can be over a mile long.
A 19882publication estimates that 30 percent of domestic oil and gas wells produced some TENORM. 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. However, 20 to 100 percent of the facilities in every state reported some TENORM in heater/treaters. EPA is investigating the number of unconventional wells that are impacted by TENORM.
Produced waters are waters pumped from wells and separated from the oil and gas produced. The radioactivity levels in produced waters from unconventional drilling can be significant and the volumes are large. The ratio of produced water to oil in conventional well was approximately 10 barrels of produced water per barrel of oil. According to the American Petroleum Institute (API), Exit 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 treated for reuse.
Scales are normally found on the inside of piping and tubing. 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 17.76 Bq/g (480 pCi/g). It can be much higher (as high as 14, 800 Bq/g or 400,000 pCi/g) or lower depending on regional geology. Scale in gas wells and equipment can also contain the radon progeny lead-210 (Pb-210) and polonium-210 (Po-210) (see below).
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 used in conventional drilling 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 2.775 Bq/g (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 999 Bq/g (27,000 pCi/g) in lead deposits and sludge.
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. More recently, unconventional drilling in shale deposits have changed the geographic areas impacted and the amount of contaminated equipment.
According to an API industry-wide survey from the 1990s, approximately 64 percent of the gas producing equipment and 57 percent of the oil production equipment showed radioactivity at or near background levels for conventional sites. TENORM radioactivity levels tend to be highest in water handling equipment. Average exposure levels for this equipment were between 0.0077389 - 0.01032 microcoulombs per hour (µC/hr) (30 - 40 microroentgens per hour (μR/hr)), which is about five 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 0.007739 - 0.01806 µC/hr (30 - 70 μR/hr). Exposures from some oil production and gas processing equipment exceeded 0.258 µC/hr (1 milliroentgen per hour).
Gas plant processing equipment is generally contaminated on the surface and in the internals by lead-210 (Pb-210) and polonium-210 (Po-210). 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 and lead-210. Polonium-210 is an alpha emitter with a half-life of 140 days. Lead-210 is a weak beta and gamma emitter with a half-life of 22 years.
1 Overview of Exploration and Production: Waste Volumes and Waste Management Practices in the United States, prepared for The American Petroleum Institute by ICF Consulting, May 2000. (112 pp, 427.05 K, About PDF) Exit
2 Development and Operation of a NORM Processing and Disposal Facility for the U.S. Oil and Gas Industry, published in the CRCPD Publication 88-2, 19th Annual Conference on Radiation Control, May 18 – 21 1987, Boise, ID. CRCPD, Frankfort KY.
3 Management and Disposal Alternatives for NORM Wastes in Oil Production and Gas Plant Equipment, prepared by Rogers and Associates Engineering Corporation for the American Petroleum Institute (RAE-8837/2-2), May 1990.
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 and 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 - 1100 picocuries per gram (pCi/g) (9.99 – 40.7 Bq/g). Unconventional drilling practices focus on the use of tanks instead of pits.
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.
The average concentration of the radium in the oil and gas wastes at offsite and onsite disposal facilities is approximately 4.44 Bq/g (120 pCi/g).
Sludges containing elevated TENORM are now dewatered and held in storage tanks for later disposal.
The produced waters from oil and gas wells are now generally reinjected into deep wells or recycled. This disposal method appears to pose no added radiological risks as long as the concentration of the radioactive material is the same or lower concentration as 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. 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.
TENORM contamination in U.S. oil production waste came to the attention of industry and government in 1986. During routine well work in Mississippi, barium sulfate scale in tubing was found to contain elevated levels of radium-226 and thorium-232.
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 could include oil and gas maintenance workers and nearby residents or office workers.
Oil and Gas Maintenance Workers
Maintenance workers include those who work directly on top of uncovered waste sites. Potential risks assessed for these workers include inhalation of radioactive dust and direct exposures to gamma radiation. 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 very low, but include:
- Direct gamma radiation.
- Inhalation of contaminated dust.
- Inhalation of downwind radon.
- Ingestion of contaminated well water.
- Ingestion of food contaminated by well water.
- Ingestion of food contaminated by dust deposition.
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 Part N Subcommittee of the Conference of Radiation Control Program Directors Exit has developed model state regulations for the control of NORM (Part N of Suggested State Regulations for Control of Radiation). 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 Texas has NORM regulations similar to Part N regulations. 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.