Elsevier

Agricultural Water Management

Volume 206, 30 July 2018, Pages 124-134
Agricultural Water Management

Review
Reusing oil and gas produced water for irrigation of food crops in drylands

https://doi.org/10.1016/j.agwat.2018.05.006Get rights and content

Highlights

  • The review estimates the volume of produced water (PW) generated in drylands.

  • Soil salinization and sodification are the main risks related to irrigation with PW.

  • PW quality, treatment and conveyance costs limit the reuse potential in irrigation.

  • PW reuse in irrigation is relevant in water-scarce and energy-rich areas.

  • More research is needed on the sustainability of irrigation with PW in hyper-arid zones.

Abstract

Water scarcity severely affects drylands threatening their food security, whereas, the oil and gas industry produces significant and increasing volumes of produced water that could be partly reused for agricultural irrigation in these regions. In this review, we summarise recent research and provide a broad overview of the potential for oil and gas produced water to irrigate food crops in drylands. The quality of produced water is often a limiting factor for the reuse in irrigation as it can lead to soil salinisation and sodification. Although the inappropriate use of produced water in irrigation could be damaging for the soil, the agricultural sector in dry areas is often prone to challenges in soil salinity. There is a lack of knowledge about the main environmental and economic conditions that could encourage or limit the development of irrigation with oil and gas effluents at the scale of drylands in the world. Cheaper treatment technologies in combination with farm-based salinity management techniques could make the reuse of produced water relevant to irrigate high value-crops in hyper-arid areas. This review paper approaches an aspect of the energy-water-food nexus: the opportunities and challenges behind the reuse of abundant oil and gas effluents for irrigation in hydrocarbon-rich but water-scarce and food-unsecured drylands.

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water (which naturally occurs in significant quantities in the reservoir with the hydrocarbons) and water that has been withdrawn from another source, injected into the O&G reservoir, and returns to the surface with the hydrocarbons (e.g. water injected for enhanced oil recovery and for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.

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