This paper presents the results of an analysis of volumes and chemical composition of produced water (PW) accompanying oil production from five of the largest oilfields in the world situated in Basrah, Iraq. PW is potentially a valuable water resource particularly there where the ramp up of oil production puts further strains on water and the environment in an area already having severe water shortages. PW should therefore be seen as part of the country's strategic water reserves rather than as effluent. This study gives first estimates of anticipated PW volumes correlated to peak oil production and water consumption needs with time up to 2035. At least a fivefold increase of PW within the next two decades relative to the current 1 Mbbl/d can be anticipated. The estimated PW quantity before 2030 represents nearly a third of water injection or salt-tolerant plant irrigation needs. These quantities and the chemical composition of PW from these fields indicate that quality standards for these purposes can be technically attained and sustained for use in Basrah.

INTRODUCTION

Produced water (PW) is the water that accompanies the petroleum during oil and gas production and represents the largest waste stream in the petroleum industry. It tends to be heavily contaminated with immiscible oil and organics, suspended solids, salts, heavy metals, and radioactive components. The worldwide estimate of its volume is around 200 Mbbl/d (1 barrel (bbl) = 159 L) which is about three times the oil production rate (Lynch 2006). Particularly in arid, oil-producing regions, PW is a viable option for addressing the increasing mismatch between limited water resources and rising water demand. Discharging such effluent can pollute surface water, soils, and ground water. If PW is treated, it could be a significant alternative water resource for various needs as injection to enhance oil recovery and irrigation purposes, providing a sustainable water balance for the future especially in the major oil producing countries.

Iraq is one such country that can tap into PW production. At present Iraq is one of the top three countries in the world with largest oil exports and reserves. About 75% of the total oil reserves in Iraq are concentrated in the giant and super-giant oilfields in the southern provinces with over 55% in and around the province of Basrah (IEA 2012).

The quantity and quality of the available water resources in this region have been sharply declining while the demand is increasing due to population growth and economic development, making it necessary to look for alternative resources (Al-Furaiji et al. 2014).

The objective of this paper is to quantify the available volumes and typical quality of PW for the five super-giant oilfields in Basrah province. Prospects are made here up to the year 2035 and cover what is expected to be the most active oil production period based on International Energy Agency (IEA) estimations. Available data from different oilfields are studied to evaluate the water needs and production in Iraq's southern region where the oilfields are situated. The approach and findings in this paper on possible alternatives for reuse of the treated PW can also be relevant for other countries and situations. This study advocates using PW if quantities are sufficient as an additional water resource for specific purposes, as in the example of Basrah and other oil regions in the world.

WATER CONSUMPTION AND PRODUCTION IN OIL INDUSTRY

Upstream oil production and water consumption and production are closely linked. The petroleum industry is a large consumer of freshwater and generator of polluted water. The quantities of injected water (used) and wastewater (produced) vary considerably depending on the geographic location of the field, its geological formation, the type of hydrocarbon being produced, production method, and oil field's age (Clark & Veil 2009).

Water consumption

Water is extensively consumed throughout an oilfield's production life at the various stages of the production process. During the drilling stage, water is mixed with clay and used as drilling mud to carry rock cuttings to the surface and cool the drill bit. In the following hydraulic fracturing stage fracking fluid (water, sand, and chemicals) is pumped into deep formations at high pressure to stimulate reservoir rock to produce oil. During the ‘primary oil recovery’ phase, the natural reservoir pressure is sufficient to force oil into a wellbore. Over time, the production from a well starts to decline. During the ‘secondary oil recovery’ phase, water injection is commonly used to boost declining pressure and force the oil from the reservoir. An early start of the secondary oil recovery phase commonly leads to higher oil recovery rates (Lyons & Plisga 2005). Water injection requires a large amount of good quality water, ranging from one to three barrels of water per barrel of oil produced, depending on the oil type, production strategy, and well age (Veil & Quinn 2008). Finally, the extracted crude oil normally contains relatively high content of salts and salt precursors (nitrogen and sulfur compounds) which can cause corrosion and plugging in columns and associated equipment. Freshwater with added emulsifiers is needed to wash the extracted crude oil in a de-salter process.

Water production

Crude oil extraction produces different quantities and qualities of wastewater during the various stages of production process referred to as PW. After the first month, most of the used fluid during drilling and fracturing stages returns as flow-back wastewater. During the production stage, the produced wastewater is the formation water which is presented naturally in the reservoir. When the oilfield matures, the waste of flood water (the water injected into the formation) will be added to this type of wastewater. As a result, PW volumes increase with age of the well. In Oman a water content (cut) has been observed as high as 93% (Al-Mahrooqi et al. 2007; GWI 2011). PW properties vary widely depending on the geological formation, production process, the type of hydrocarbon produced, and the lifetime of the reservoir (Clark & Veil 2009).

The average US water:oil ratio is estimated to be about seven barrels of PW for each barrel of oil produced (Veil et al. 2004). The current water:oil ratio is estimated at 2:1 to 3:1 worldwide, translating to a water cut of 50–75% (Duhon 2012). The PW is often heavily contaminated with dissolved, immiscible, and suspended material, both natural and artificially added during drilling and hydraulic fracturing processes (Shaffer et al. 2013).

WATER AND OIL RESOURCES IN IRAQ

Water resources

Surface water in Iraq flows primarily through Euphrates and Tigris rivers, both of which originate in Turkey as shown in Figure 1. In the deltas of the two rivers in the south of Iraq there are some of the largest wetlands in southwest Asia covering 15,000–20,000 km2. After the confluence of these rivers into Shatt Al-Arab, water drains into the Arabian Gulf from Al Basrah city (Partow 2001).

Figure 1

(a) River basins and oilfields in Iraq (Al-Ameri et al. 2011); (b) super-giant oilfields in Basrah (Al-Ameri et al. 2009).

Figure 1

(a) River basins and oilfields in Iraq (Al-Ameri et al. 2011); (b) super-giant oilfields in Basrah (Al-Ameri et al. 2009).

Over recent decades, the surface water availability throughout Iraq has been substantially reduced due to the many dams built by Turkey, Iran and Syria. Water flowing into Iraq has been reduced drastically by more than 75% of the flow in 1990 (Jongerden 2010). The upstream damming combined with massive drainage of the marshes carried out from 1985 until 2000 resulted in irreversible changes to the region (Partow 2001). All these factors, combined with increasingly warmer weather conditions, contributed to the shortages of freshwater in Iraq's southern provinces. An emergency situation is expected to arise around 2020 because the annual 4 km3 of water remaining as surplus in the two main rivers will be insufficient (Al Obaidy & Al Khateeb 2013).

Oil resources

Iraq is one of the world's main oil-producing countries with the third largest proven oil reserves and the second largest oil exporter in the world (Muttitt 2005). It has nine fields that are considered ‘super-giants’ (over 5 billion bbl of reserves) as well as 22 known ‘giant’ fields (over 1 billion bbl of reserves). The cluster of super-giant and giant fields in the south of Iraq forms the largest known concentration of such oilfields in the world and accounts for two-thirds of the country's proven oil reserves. There are five super-giant oilfields in the southern region: Rumaila, West Qurna, Zubair, Majnoon, and Nahr Umr, containing about 55% of Iraq's total oil reserves.

The IEA's central case projects that Iraq's oil production will increase to 6.1 Mbbl/d by 2020 and reach 8.3 Mbbl/d by 2035. Oil production increase is mainly driven by the five southern super-giant oilfields. Based on data from Iraq's Ministry of Oil and the IEA estimates, we can predict the productivity of the five super-giant oilfields in Basrah up to 2035, as shown in Figure 2 (IEA 2012).

Figure 2

Estimated oil production for five super-giant oilfields in Basrah up to 2035.

Figure 2

Estimated oil production for five super-giant oilfields in Basrah up to 2035.

ESTIMATION OF WATER CONSUMPTION, PW QUANTITY, AND QUALITY

Consumed water

The required water for injection in Basrah province is estimated using the world average range of 1–3 barrels of water per barrel of oil (Veil & Quinn 2008). We estimated the amount of injection water (Figure 3) by multiplying the oil production (Figure 2) by a factor increasing from 1 to 3 over the period from 2010 to 2035 depending on the oil field's age and production strategy.

Figure 3

Estimated water injection quantities for the five super-giant oilfields in Basrah.

Figure 3

Estimated water injection quantities for the five super-giant oilfields in Basrah.

Produced water

The water cut is the fraction of water in the produced fluid. The water cut usually increases with increasing age of the oilfield depending on the amount of formation water and injected water for enhancing oil recovery. At some point an oil well becomes uneconomical as revenue from a declining oil supply fails to cover the costs of processing the high water fraction (Sams & Zaouk 2000).

Every oilfield has a unique production profile which could be long or short depending on the total volume of oil present and production rate. All the oilfields go through build-up, plateau production, and decline phases (Luo & Zhao 2012). Southern Iraq's oilfields are in different phases; the Rumaila oilfield will enter its depletion phase in 2020, Zubair, Majnoon, and Nahr Umr oilfields will reach their plateau phases by about 2023, while West Qurna will remain in the buildup phase until 2035.

To predict the amount of PW, we need to estimate the present and future water cut of these oilfields. Various oilfield profiles were studied: the North Ain Dar Saudi oilfield and the North East Atlantic oilfields (Alhuthali et al. 2005; Igunnu & Chen 2012). Based on these profiles, at the peak oil production rate the water cut is less than 50% (one barrel of water with each barrel of oil). As a result, the water cut of these oil fields is estimated as follows: the water cut of Rumaila was 25% in 2004 (IEA 2005) and it will reach 45% when its depletion phase starts in 2020 followed by a further increase to 60% in 2030; Zubair, Majnoon, and Nahr Umr are predicted to have a water cut of 35% by 2030, while the water cut of West Qurna is estimated to reach 30% in 2030.

Based on these estimations and Figure 3, we can make an estimate of PW volume in time for the five super-giant oilfields in Basrah as plotted in Figure 4. The total PW rate is estimated to reach 2 and 4.7 Mbbl/d in 2020 and 2035, respectively.

Figure 4

The estimated volumes of PW for the five super-giant oilfields in the south of Iraq.

Figure 4

The estimated volumes of PW for the five super-giant oilfields in the south of Iraq.

Moreover, this PW is heavily polluted and is considered as brine water because of its extremely high salinity (total dissolved solids (TDS) > 35,000 mg/L). Table 1 shows PW characteristics of (North and South) Rumaila, Zubair, and West Qurna oilfields.

Table 1

Characteristics of the produced water of the four oilfields (Al-Rubaiea et al. 2013)

Water quality parameter (North and South) Rumaila Zubair West Qurna 
pH (−) 4.1–4.8 6.6 4.9 
Total dissolved solids (TDS) (mg/L) 246,000–247,000 268,000 300,000 
Total suspended solids (TSS) (mg/L) 141–260 110 75 
Bicarbonate as (CaCO3) (mg/L) 40,000–54,000 50,000 43,000 
Oil content (mg/L) 36–53 66 57 
Chemical oxygen demand (COD) (mg/L) 800–1,400 1,800 1,500 
Total organic carbon (TOC) (mg/L) 300–500 610 520 
Sulfate (mg/L) 108–116 104 94 
Iron (mg/L) 10–18 0.6 0.61 
Manganese (mg/L) 1–2.5 2.2 1.5 
Calcium (mg/L) 17,000–13,000 14,000 12,000 
Magnesium (mg/L) 1,900–2,600 3,600 3,100 
Sodium (mg/L) 89,000–91,000 87,000 98,000 
Chloride (mg/L) 138,000–141,000 134,000 151,000 
Water quality parameter (North and South) Rumaila Zubair West Qurna 
pH (−) 4.1–4.8 6.6 4.9 
Total dissolved solids (TDS) (mg/L) 246,000–247,000 268,000 300,000 
Total suspended solids (TSS) (mg/L) 141–260 110 75 
Bicarbonate as (CaCO3) (mg/L) 40,000–54,000 50,000 43,000 
Oil content (mg/L) 36–53 66 57 
Chemical oxygen demand (COD) (mg/L) 800–1,400 1,800 1,500 
Total organic carbon (TOC) (mg/L) 300–500 610 520 
Sulfate (mg/L) 108–116 104 94 
Iron (mg/L) 10–18 0.6 0.61 
Manganese (mg/L) 1–2.5 2.2 1.5 
Calcium (mg/L) 17,000–13,000 14,000 12,000 
Magnesium (mg/L) 1,900–2,600 3,600 3,100 
Sodium (mg/L) 89,000–91,000 87,000 98,000 
Chloride (mg/L) 138,000–141,000 134,000 151,000 

Currently, part of this PW is disposed of through injection into Dammam formation (Al-Razaq 2012) causing pollution of underground aquifers. The other part is discharged directly to the surrounding environment leading to environmental problems in the region as the oil and organics, heavy metal, and radioactive materials contents are very toxic for plants, animals, and humans. These pollutants can be absorbed by the ground and pollute the ground water. In addition, the high salinity is considered as a major contributor to toxicity and it reduces water uptake by lowering the soil osmotic potential and permeability.

RECYCLING OF PW

Water recycling refers to reusing treated wastewater for beneficial purposes such as re-injection, irrigation, and even drinking water. Recycling water curbs the amount of consumed freshwater and decreases the adverse effects of wastewater discharge. An example where PW is reused successfully already in a comparable environment to that in Iraq is in Oman. There the Nimr project plant handles on average about 45,000 m3/d of PW which is then used for irrigation (Breuer & Al-Asmi 2010).

A choice is made in this study to consider PW for injection and (or) irrigation purposes. The main water quality parameters of concern are oil and hydrocarbons, suspended solids, and salinity. Membrane technology has shown promise for converting a waste fluid to a usable resource. However, PW can cause severe fouling problems on most membranes (Burnett 2008). Although there are some methods to reduce fouling problems (Ahmadun et al. 2009), PW should be processed through different separators and filters as pre-treatment steps to reduce oil and hydrocarbons, gas, and (suspended and dissolved) solids.

There are different technologies that can be used to reduce hydrocarbon content effectively such as membrane bioreactors, wetlands, nanofiltration, and adsorption technologies. The dissolved gas can be separated by gas separator technology, while the suspended solids can be reduced by filtration (GWI 2011). Application of softening as pre-treatment is effective in reducing carbonate ions which form the main precipitations (scales) in the desalination process (Gryta 2010). The most effective technologies for desalination of high-salinity PW are mechanical vapor compression, membrane distillation, and forward osmosis (Shaffer et al. 2013).

Reuse for re-injection

The demand for water injection to enhance oil production is high. As previously discussed, this rate will further increase as future oil production in Iraq ultimately rises to designated level. At present, Garmat Ali River (which receives its water from Euphrates) is the main water source for the southern oilfields (Jaffe 2006), but it will be insufficient for the anticipated increased water demand of the future.

To solve this problem, Iraq has chosen the Common Seawater Supply Facility (CSSF) Project to bring in and treat seawater from the Arabian Gulf (TDS = 50,000 mg/L) (Alnouri & Linke 2013) to supply the southern oilfields with injection water. The project will start in 2017 with an initial phase of 2 Mbbl/d and will be developed in stages over the following years: 4 Mbbl/d in 2018, 6 Mbbl/d in 2021, and 8 Mbbl/d in 2027. Before using this water for injection, it should be treated to meet the water injection quality standards. Meeting these quality standards is essential for preserving the permeability of a reservoir formation; otherwise, serious problems can occur such as corrosion of pipes and clogging of the formation resulting in needing higher than anticipated injection pressures then loss of affected injection wells (Bader 2007). The most critical parameters for injection are total suspended solids (TSS) (should be less than 10 mg/L) and TDS (should be in the range of 1,000–12,000 mg/L). About 50% more oil can be produced if low salinity water (TDS < 4,000 mg/L) is injected into the reservoir compared with using higher salinity water (Webb et al. 2003).

As the CSSF will be insufficient to provide enough injection water for the oilfields in the south of Iraq, treated PW can be used as a supplement. Treated PW can contribute in providing up to 35% of the required water for injection in the five southern super-giant oilfields (see Figures 3 and 4).

Reuse for irrigation

In the southern region of Iraq, water shortage is the most important factor that affects agricultural production and water-reliant industries. According to irrigation water quality standards, TSS and TDS values should be less than 30 and 2,500 mg/L, respectively, while the oil content should be less than 0.5 mg/L (Sirivedhin et al. 2004). The solids content is important because high TSS reduces soil porosity while high TDS reduces water uptake by plants by increasing the soil osmotic potential.

The date palm is a main commercial plant in Basrah, and it is considered as one of the most salt-tolerant plants found in the region. The water shortage for the date palms irrigation is estimated at 600 Mm3/year (13.8 Mbbl/d) (Al-Furaiji et al. 2014). At present, the treated PW could meet 8% of the water needed for date palms in Basrah and could overcome 15% of the shortage water in 2020 and more than 33% in 2035.

CONCLUSION

Upstream oil production and water consumption and production are closely linked. To extract oil huge amounts of fresh water are used in the various stages of the oil production process (drilling, fracturing, injection and washing). Part of this water in combination with water naturally present in the formation is extracted again with the oil producing a large amount of wastewater referred to as PW.

In Basrah province in the south of Iraq, five super-giant oilfields are located which contain 55% of Iraq's oil reserves. The production rate of these oilfields is expected to increase to 4.4 Mbbl/d in 2020 and 5.7 Mbbl/d in 2035. It is estimated that this requires about 8.5 Mbbl/d of injection water in 2020 and 13.7 Mbbl/d in 2035. This will generate an increasing amount of PW estimated at 2 Mbbl/d in 2020 and 4.7 Mbbl/d in 2035. In Iraq PW is currently discharged directly into the environment with devastating impacts. When treated, this PW could be used for beneficial purposes. As the PW is heavily contaminated it needs to be treated with advanced technologies before reuse. A possible application of the treated PW is as injection water for enhanced oil recovery. The PW makes up 23% (in 2020) to 35% (in 2035) of the required injection water. This is a valuable addition to the planned seawater treatment plant that is anticipated to supply part of the injection water (8 Mbbl/d in 2027). Another potential application of the treated PW is as irrigation water. As PW in south Iraq has high salinity, it may be most suitable for irrigation of salt-tolerant plants such as date palms. By 2035, treated PW could make up 33% of the irrigation water required for date palms in Basrah province. This study shows that PW in the south of Iraq forms a substantial amount that after treatment could be used as a valuable resource saving the environment and fresh water resources in a region with increasing water shortages.

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