ReviewReusing oil and gas produced water for irrigation of food crops in drylands
Graphical abstract
Introduction
The oil and gas (O&G) industry produces large volumes of water during the extraction, processing, and refining of hydrocarbons. The water that is brought to the surface with hydrocarbons during extraction is termed ‘produced water’ (PW); this often comprises both formation water (which naturally occurs in significant quantities in the reservoir with the hydrocarbons) and water that has been withdrawn from another source, injected into the O&G reservoir, and returns to the surface with the hydrocarbons (e.g. water injected for enhanced oil recovery and for hydraulic fracturing) (Engle et al., 2014). In terms of volume, PW is by far the largest by-product or waste stream associated with the O&G industry (Veil, 2011). In certain conditions, PW can be reused for beneficial purposes such as agricultural irrigation, but, the volume of PW currently reused this way represents only a small proportion of the total PW generated. Nonetheless, beneficial reuse of PW is growing (Burnett, 2004; Clark and Veil, 2015) and could provide a substantial volume of irrigation water to crops located near O&G facilities in drylands (Guerra et al., 2011).
In this paper, drylands are defined by a precipitation to potential evapotranspiration ratio below 0.05 i.e. hyper-arid climate, up to 0.65 i.e. dry sub-humid climate (Barrow, 1992; FAO, 2016; Safriel et al., 2006). Many drylands contain massive hydrocarbon resources (e.g. the Persian Gulf, the Western USA, the Gulf of Mexico, the Libyan Desert or the Caspian Sea countries). There are also large coal resources from which gas and synthetic fuels are produced in the USA, China, Australia, and South Africa (Fig. 1). The Middle-East North Africa region, which is one of the most populated dry areas (World Bank, 2016); represents about 33% of the oil production and 23% of the gas production in the world (EIA, 2016).
Drylands occur on all continents (Safriel et al., 2006), cover 41% of the earth’s landmass (Millenium Ecosystem Assessment, 2005) and are projected to expand, partly due to climate change (Feng and Fu, 2013). These regions are inhabited by 2.1 billion people, many of whom live in developing countries and are directly dependent on the land’s natural resources (UN, 2010). Projections estimate that half of the global population will live in regions with high water scarcity by 2030 (UN, 2012). Drylands are an important component of the total agricultural land area as well. About 50% of the arid and semi-arid area is used for agriculture (Gratzfeld, 2003), drylands grow 44% of the world’s food and support 50% of the world’s livestock (Reid, 2014). In drylands, agriculture represents a major economic activity and approximately a third of the population living in these zones depend on agriculture particularly in Africa and in Asia (CGIAR, 2015). Within developed countries, drylands have also significant economic importance. For instance, California represents 13% of the US GDP making this dry state the major contributor to America’s national wealth (US Department of Commerce, 2015). California also produces around 70% of the fruit and tree nuts, 55% of the vegetables, 10% of the cotton and about 30% of the rice produced in the USA (US Department of Agriculture, 2015). However, agriculture and populations in drylands are under constant threat of water shortage. In fact, drylands are characterised by physical water scarcity because they are naturally prone to lack of water due to their negative water balance (i.e. low precipitation and high evapotranspiration) (Gassert et al., 2014). In addition, fresh water availability can also be reduced by water pollution (NSW Government, 2011) or seawater intrusion (Qadir and Sato, 2015) which can contaminate the already limited fresh water resources. Climate change is projected to increase water scarcity in most drylands, affecting both rain-fed and irrigated agriculture (Pedrick, 2012). As water resources are diminishing, water users (i.e. industry, agriculture, households and the natural environment) are competing more and more for access to water (El-Zanfaly, 2015; Freyman, 2014; Qadir and Sato, 2015).
Therefore, the pressure on water resources from the O&G industry in drylands is expected to intensify and is likely to exacerbate competition and conflicts between water users, and especially between irrigated farming and unconventional O&G firms which use fresh water resources (Galbraith, 2013; Hitaj et al., 2014). Reusing O&G PW for the irrigation of food crops could contribute considerably to improve the sustainability of irrigated agricultural systems in drylands.
This structured review paper aims to provide a critical review of the potential of O&G PW for the irrigation of food crops in drylands. It starts by providing a review of the volumes and qualities of PW from around the world, followed by a discussion of its treatment and management practices. Finally, the potential for reuse of PW in agriculture is discussed and experiences of irrigation with PW are reviewed in order to identify the main risks associated with using PW in practical conditions. The quality of PW is also discussed from an agricultural viewpoint in order to highlight the agronomic and environmental risks associated with reuse and the perspectives for adapting PW to irrigation.
Section snippets
Volume of produced water
The water-to-oil (WOR) and water-to-gas (WGR) ratios are indicators used to quantify the volume of PW generated compared to the volume of oil or gas produced. Although strictly dimensionless, the O&G industry generally expresses the ratios as barrels (159 L) of water per barrel of oil or million cubic feet of gas. At the world scale, the average WOR was about 3:1 in the 2000s (Khatib and Verbeek, 2002), and is probably nowadays closer to 4:1, but it can locally range from as low as 0.4 to as
Quality of produced water
PW contains a mixture of organic and inorganic materials (Table 2) including dissolved and dispersed oil, dissolved formation minerals, production chemical compounds, production solids (e.g. formation solids, corrosion and scale products, bacteria, waxes, and asphaltenes), naturally occurring radioactive materials (NORM) and dissolved gases (Deng et al., 2008; Ekins et al., 2007; Fakhru’l-Razi et al., 2009; Hansen and Davies, 1994; McCormack et al., 2001; Neff, 2002; Neff et al., 2011;
Management of produced water
Due to its complex composition, PW needs to be managed in order to avoid environmental damage. Treatment and reuse or disposal options depend on the constituents of PW, the location of the oil or gas field (e.g. onshore or offshore) and the environmental regulation of the territory where the hydrocarbon is produced. For example, oil and grease receive the most attention for both onshore and offshore PW, whereas salt content is of concern for onshore PW.
Experience of irrigation with oil and gas produced water
Among the possible beneficial reuses of PW, agricultural irrigation (especially of food crops) could be particularly relevant in drylands. Table 4 presents theoretical research, laboratory and field experiments, as well as examples of large-scale use of PW for irrigation in different parts of the world. Table 4 helps to identify the challenges faced when PW is used for irrigation in dry zones. It also supports the idea that PW in conjunction with adapted management has an important potential to
Conclusion
A significant part of current and forecast volumes of PW will be produced in drylands where water scarcity demands alternative irrigation water sources. PW could be an effective resource in drylands; indeed, at the global scale, about 45% of PW is discharged, disposed of, or not reused in a beneficial way. However, quality remains the principal challenge for the reuse of this massive quantity of PW in irrigation. In fact, most PW are high in salts ([TDS] = 35–472 000 mg/L) and sodium
Conflict of interest
None.
Acknowledgments
This work was made possible by the support of a National Priorities Research Programme (NPRP) grant from the Qatar National Research Fund (QNRF), grant reference number NPRP8-1115-2-473. The statements made herein are solely the responsibility of the authors.
References (145)
- et al.
Chemical and physical characterization of produced waters from conventional and unconventional fossil fuel resources
Chemosphere
(2011) - et al.
Can crops be irrigated with sodium bicarbonate rich CBM deep aquifer water? Theoretical and field evaluation
Ecol. Eng.
(2008) - et al.
Desalination techniques – a review of the opportunities for desalination in agriculture
Desalination
(2015) - et al.
Zero emissions of oil in water from offshore oil and gas installations: economic and environmental implications
J. Clean. Prod.
(2007) - et al.
Assessment of potential risks associated with chemicals in wastewater used for irrigation in arid and semiarid zones: a review
Agric. Water Manag.
(2016) - et al.
Review of technologies for oil and gas produced water treatment
J. Hazard. Mater.
(2009) - et al.
Irrigation with coalbed natural gas co-produced water
Agric. Water Manag.
(2008) - et al.
Feasibility of desalination as an alternative to irrigation with water high in salts
Desalination
(2017) - et al.
Assessing the net benefits of using wastewater treated with a membrane bioreactor for irrigating vegetables in Crete
Agric. Water Manag.
(2010) - et al.
Analysis of oilfield produced waters and production chemicals by electrospray ionisation multi-stage mass spectrometry (ESI-MSn)
Water Res.
(2001)