Agricultural Use

Fact Sheet - Agricultural Use

   
 
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According to estimates by the U.S. Geological Survey (Hutson et al. 2004), the U.S. agricultural community withdrew more than 140 billion gallons per day (more than 3 billion bbl/d) of fresh water for irrigation, livestock, and aquacultural use in 2000. Many oil and gas wells are located in areas of the country that are characterized by arid climates and scarce fresh water resources. Produced water meeting the water quality requirements of agricultural users offers the potential to supplement and replace existing water supplies. Ayers and Westcot (1994) provide an excellent reference on water quality requirements for agricultural uses. This fact sheet describes the use of produced water for irrigation, livestock watering, wildlife watering, and managed wetlands.

Perhaps the most significant barrier to using produced water for agricultural purposes involves the salt content of the water. Most crops do not tolerate much salt, and sustained irrigation with salty water can damage soil properties. In addition, if livestock drink water containing too much salt, they can develop digestive disorders.

However, not all produced water is equally salty. For example, some of the coal bed methane fields in Wyoming's Powder River Basin generate relatively fresh water. However, in addition to the salt content, the relative proportion of sodium to other ions is important because excessive sodium is harmful to soils. Soil scientists use the term "sodium adsorption ratio" (SAR) to characterize the ionic proportions. The SAR is defined as the milliequivalent weight of sodium divided by the square root of the sum of the milliequivalent weights of calcium and magnesium, divided by 2, or in equation format:

SAR = Na+1 / [(Ca+2 + Mg+2)/2]0.5, with Na, Ca, and Mg expressed as meq/L.

Since produced water in the Powder River Basin frequently exhibits relatively high sodium concentrations compared to those of calcium and magnesium, the SAR of that water tends to be high. These waters can be used for some purposes without treatment, but often require some level of treatment to reduce the SAR. When more salty produced waters are intended for agricultural use, the cost-benefit and cost-effectiveness of treatment to remove salinity and improve SAR become important considerations.

  Irrigation of crops.
Irrigation of crops; Source: U.S. Dept. of Agriculture

Using Produced Water for Crop Irrigation

ALL (2003) summarizes crop irrigation water quality requirements, noting that the three most critical parameters include salinity, sodicity, and toxicity. Salinity is expressed as electrical conductivity in units of microSiemens per cm (µS/cm) (previously, mmhos/cm). Crops exhibit varying susceptibility to salinity. When salinity rises above a species-specific threshold, crop yields decrease.

Excess sodium can damage soils. Higher SAR values lead to soil dispersion and loss of soil infiltration capability. When sodic soils are wet, they become sticky, and when dry, they form a crusty, nearly impermeable layer. Some trace elements in produced water can cause harmful effects to plants when present in sufficient quantities. ALL (2003) notes that the most common sources of plant toxicity include chloride, sodium, and boron.

Another source of information on the effects of applying produced water to soils is a manual developed for the American Petroleum Institute on remediation of soils that have experienced produced water spills (API 1997). The manual offers a detailed technical guide addressing the impacts of salinity and sodium on soils and vegetation. The authors of the manual have taught a series of workshops covering the same subject.

Operators intending to use coal bed methane (CBM) water without causing long-term harm to crop and soil employ "managed irrigation." This technique involves careful monitoring of the soil chemistry. Different soil supplements are added to provide the necessary chemical and mineral balance. Some examples of managed irrigation are described below.

ALL (2003) provides two case examples from Wyoming. The first project was conducted by Fidelity Exploration and Production. They irrigated livestock forage using only CBM water on some plots, and surface water/CBM water blends on other plots. Both resulted in adequate crop production. Yet, the CBM water had to be applied at a higher rate because the plants did not utilize it as efficiently as the surface water.

The second project was conducted by Williams, a CBM producer. Large land areas were irrigated areas that previously had supported only the local drought-tolerant vegetation. Following irrigation with CBM produced water, the land was able to support healthy grass crops that served as feed for livestock. Between watering intervals, Williams provided gypsum and other soil supplements to counteract the high SAR in the produced water.

DeJoia (2002) describes a successful managed irrigation project. After two years of applying soil amendments and CBM produced water, the test sites were converted from overgrazed range land to highly productive grasslands yielding livestock and wildlife benefits.

Paetz and Maloney (2002) discuss a project using 12,500 bbl/d of CBM water to irrigate 100 acres of arid land to produce a forage crop. The carefully managed approach resulted in the successful production, harvesting, and sale of the forage crop.

Harvey et al. (2005) describe several successful case studies of managed irrigation to beneficial reuse applications of CBM produced water.

Although most irrigation projects using produced water are found in the Rocky Mountain region, Brost (2002) describes a complex system used by ChevronTexaco to treat produced water in the Kern River field in central California. The treatment system provides about 480,000 bbl/d of water for irrigating fruit trees and other crops, and recharging shallow aquifers. Another 360,000 bbl/d of water are further purified and used to make steam at a cogeneration facility.

Using Produced Water for Subsurface Irrigation
As described above, CBM produced water can be used for surface irrigation if combined with soil amendments such as gypsum. Gypsum dissolves in the irrigation water and provides soluble calcium to minimize the harmful effect of high-sodium produced water on soil infiltration. Although surface soils are often depleted of gypsum by millennia of rainwater leaching, significant amounts of gypsum occur naturally in the subsoil. Subsurface irrigation uses a network of buried pipes with emitters to apply high-sodium produced water directly to soil horizons that are gypsum-enriched. This practice enables CBM produced water to be used for irrigation without soil permeability problems until the gypsum in the subsoil is exhausted, These systems are designed to last for 10 to 15 years, if well cared for. However, there are SDI systems that have operated for more than 20 years (BeneTerra undated). Subsurface irrigation has other advantages over surface irrigation including: 1) year-round application (surface irrigation only can be used when temperatures are above freezing; 2) near 100% utilization of applied water (15-20% of surface applied water evaporates); 3) soil warming to hasten crop emergence; and 4) the prevention of shallow-rooted weeds.BeneTerra LLC has developed a subsurface irrigation process that uses CBM produced water (BeneTerra undated). The process requires careful soil characterization at proposed irrigation sites to be certain that the soil contains sufficient gypsum to sustain infiltration. The application of CBM produced water is metered to ensure that the gypsum in the subsoil will maintain soil infiltration for the expected length of produced water application One BeneTerra subsurface irrigation site in Wyoming has been monitored by the US Geological Survey and the National Energy Technology Laboratory during the first three years of CBM produced water application.

photo showing BeneTerra Irrigation System using CBM produced water
BeneTerra Irrigation System using CBM produced water. Surge pond receiving CBM produced water is in the foreground. Building that houses water treatment facilities is on the far side of the pond. The green fields in the background are receiving CBM produced water via the subsurface irrigation system.

   
  Cattle drinking from tank.
Cattle drinking from tank; Source: U.S. Dept. of Agriculture

Using Produced Water for Livestock Watering 
Livestock can tolerate a range of contaminants in their drinking water (Ayers and Westcot 1994). In general, animals can often tolerate elevated levels of total dissolved solids (TDS) if they are gradually acclimated. At certain concentrations, the animals will begin to show some impairment. Water with a TDS level of less than 1,000 ppm is considered to be excellent source water. Water with TDS levels from 1,000 up to 7,000 ppm can be used for livestock but may cause diarrhea. Some CBM projects on ranch land have created impoundments or watering stations to provide CBM produced water as a drinking water source for livestock. ALL (2003) describes an example from the 7 Ranch near Gillette, Wyoming, where livestock are watered from small reservoirs and old heavy-vehicle tires used as watering tanks.

   
  Waterfowl in pond.
Waterfowl in pond; Source: South Carolina Dept. of Natural Resources

Using Produced Water for Wildlife Watering and Habitat 
Some CBM projects in the Rocky Mountain area have created impoundments that collect and retain large volumes of produced water. In some cases, these may have surface areas of at least several acres. The impoundments provide a source of drinking water for wildlife and offer habitat for fish and waterfowl in an otherwise arid environment. It is important to ensure that the quality of the impounded water will not create health problems for the wildlife. The impoundments can also offer additional recreational opportunities for hunting, fishing, boating, and bird watching. ALL (2003) presents information on siting and constructing wildlife-watering impoundments.

Aquaculture and Hydroponic Vegetable Culture 
Jackson and Myers (2002) describe greenhouse experiments to raise vegetables and fish. Different tests compared produced water and potable water as water sources. The project system used a combination of hydroponic plant cultivation (undertaken without the use of soil) and aquaculture. Tomatoes grown with produced water were smaller than their potable water counterparts. Tilapia fish (Orechromis niuloticus/aureus) raised in a tank of produced water weighed more than those raised in a tank of potable water. However, some of the fish raised in the produced water died, whereas no fatalities occurred in the potable water tank. In sum, the tests showed that produced water could serve as a water source for vegetables and fish, especially when other potable water sources are not available.

Constructed Wetlands
Researchers at Clemson University received funding from DOE in 2009 to develop constructed wetland systems for treatment and beneficial use of produced water, and to conduct scientific studies to address ecological, environmental, and regulatory concerns that limit options for managing produced water, including surface discharge. The project, in conjunction with Chevron, is described in an NETL project summary. [link to http://www.netl.doe.gov/technologies/oil-gas/Petroleum/projects/Environmental/Produced_Water/05682_WaterManagement.html] Petroleum Development Oman (PDO) operates oil and gas wells in Oman. Following a pilot study of using constructed wetlands for treating produced water, PDO has embarked on a large project using constructed reed beds to treat at least 280,000 bbl/day of produced water. Construction began in 2009, and the system is scheduled to begin operation in early 2011 (Breuer and Al-Asmi 2010)

References
ALL, 2003, "Handbook on Coal Bed Methane Produced Water: Management and Beneficial Use Alternatives," prepared by ALL Consulting for the Ground Water Protection Research Foundation, U.S. Department of Energy, and U.S. Bureau of Land Management, July.

API, 1997, "Remediation of Salt-Affected Soils at Oil and Gas Production Facilities," American Petroleum Institute Publication No. 4663, Oct.

Ayers, R.S., and D.W. Westcot, 1994, "Water Quality for Agriculture," Irrigation and Drainage Paper, 29 Rev. 1 (Reprinted 1989, 1994). Available at http://www.fao.org/DOCREP/003/T0234E/T0234E00.htm [external site].

BeneTerra, undated, BeneTerra Subsurface Drip Irrigation for Dispersal of Produced Coalbed Water. Available at http://www.beneterra.com/images/Industries_Served.pdf [PDF-external site].

Breuer, R., and S. R. Al-Asmi, 2010, “Nimr Water Treatment Project – Up Scaling a Reed Bed Trail to Industrial Scale Produced Water Treatment”, SPE 126265, presented at the SPE International Conference on Health, Safety and Environment in Oil and Gas Exploration and Production, Rio de Janeiro, Brazil, April 12–14.

Brost, D.F., 2002, "Water Quality Monitoring at the Kern River Field," presented at the 2002 Ground Water Protection Council Produced Water Conference, Colorado Springs, CO, Oct. 16 17. Available at http://www.gwpc.org/meetings/special/PW%202002/Papers/Dale_Brost_PWC2002.pdf [PDF external site].

DeJoia, A.J., 2002, "Developing Sustainable Practices for CBM-Produced Water Irrigation," presented at the 2002 Ground Water Protection Council Produced Water Conference, Colorado Springs, CO, Oct. 16-17. Available at http://www.gwpc.org/meetings/special/PW%202002/Papers/Aaron_DeJoia_PWC2002.pdf [PDF external site].

Harvey, K.C., D.E. Brown, and A.J. DeJoia, 2005, "Managed Irrigation for the Beneficial Use of Coalbed Natural Gas Produced Water in the Powder River Basin," presented at the 12th International Petroleum Environmental Conference, Houston, TX, November 7-11.

Hutson, S.S., Barber, N.L., Kenny, J.F., Linsey, K.S., Lumia, D.S., and Maupin, M.A., 2004, "Estimated Use of Water in the United States in 2000," U.S. Geological Survey Circular 1268, 46 pp. Available at http://pubs.usgs.gov/circ/2004/circ1268/pdf/circular1268.pdf [PDF external site].

Jackson, L., and J. Myers, 2002, "Alternative Use of Produced Water in Aquaculture and Hydroponic Systems at Naval Petroleum Reserve No. 3," presented at the 2002 Ground Water Protection Council Produced Water Conference, Colorado Springs, CO, Oct. 16-17. Available at http://www.gwpc.org/meetings/special/PW%202002/Papers/Lorri_Jackson_PWC2002.pdf [PDF external site].

Paetz, R.J., and S. Maloney, 2002, "Demonstrated Economics of Managed Irrigation for CBM Produced Water," presented at the 2002 Ground Water Protection Council Produced Water Conference, Colorado Springs, CO, Oct. 16-17. Available at http://www.gwpc.org/meetings/special/PW%202002/Papers/Steel_Maloney_PWC2002.pdf [PDF external site].

Veil, J.A., M.G. Puder, D. Elcock, and R.J. Redweik, Jr., 2004, "A White Paper Describing Produced Water from Production of Crude Oil, Natural Gas, and Coal Bed Methane," prepared by Argonne National Laboratory for the U.S. Department of Energy, National Energy Technology Laboratory, January. Available at http://www.evs.anl.gov/pub/dsp_detail.cfm?PubID=1715 [external site].

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