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Journal of Hazardous Materials 170 (2009) 530–551 Contents lists available at ScienceDirect

Journal of Hazardous Materials journal homepage: w.elsevier.com/locate/jhazmat

Review Review of technologies for oil and gas produced water treatment

Fakhru’l-Razi Ahmaduna,b,∗, Alireza Pendashteha, Luqman Chuah Abdullaha,

Dayang Radiah Awang Biaka, Sayed Siavash Madaenic, Zurina Zainal AbidinaDepartment of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, MalaysiaPrince Khalid Bin Sultan Chair for Water Research Centre, Civil Engineering Department, College of Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Saudi ArabiaChemical Engineering Department, Razi University, Kermanshah, Iran article info

Article history: Received 15 March 2009 Received in revised form 10 May 2009 Accepted 12 May 2009 Available online 19 May 2009

Keywords: Oilfield wastewater Produced water Oilfield brine Treatment technology abstract

Produced water is the largest waste stream generated in oil and gas industries. It is a mixture of different organic and inorganic compounds. Due to the increasing volume of waste all over the world in the current decade, the outcome and effect of discharging produced water on the environment has lately become a significant issue of environmental concern. Produced water is conventionally treated through different physical, chemical, and biological methods. In offshore platforms because of space constraints, compact physical and chemical systems are used. However, current technologies cannot remove smallsuspended oil particles and dissolved elements. Besides, many chemical treatments, whose initial and/or running cost are high and produce hazardous sludge. In onshore facilities, biological pretreatment of oily wastewater can be a cost-effective and environmental friendly method. As high salt concentration and variations of influent characteristics have direct influence on the turbidity of the effluent, it is appropriate to incorporate a physical treatment, e.g., membrane to refine the final effluent. For these reasons, major research efforts in the future could focus on the optimization of current technologies and use of combinedphysico-chemicaland/orbiologicaltreatmentofproducedwaterinordertocomplywithreuseand discharge limits. © 2009 Elsevier B.V. All rights reserved.

1. Introduction531
1.1. Origin of produced water532
1.2. Global onshore and offshore produced water production532
1.3. Factors affecting production volume of produced water532
1.4. Characteristics of produced water533
1.4.1. Dissolved and dispersed oil compounds533
1.4.2. Dissolved formation minerals533
1.4.3. Production chemical components533
1.4.4. Production solids533
1.4.5. Dissolved gases534
1.4.6. Produced water from gas fields534
1.4.7. Produced water from oil fields535
1.5. Fate and impact of produced water discharge535
1.5.1. Salinity535
1.5.2. Dispersed and soluble oil535

Contents

Abbreviations: BAF, biological aerated filter; BOD, biochemical oxygen demand; Bq/l, becquerel per liter; BTEX, benzene, toluene, ethylbenzene, and xylenes; COD, chemical oxygen demand; CAPEX, capital expenses; FWS, free-water surface; MF, microfiltration; MBR, membrane bioreactor; mg/L, milligram per liter; MWCO, molecular weight cut-off; NF, nanofiltration; O&G, oil and grease; PAHs, polyaromatic hydrocarbons; ppb, parts per billion; ppm, part per million; RO, reverse osmosis; SBR, sequencing batch reactor; SMZ, surfactant-modified zeolite; S, suspended solids; SF, subsurface flow; TDS, total dissolved solids; TPH, total petroleum hydrocarbons; UF, ultrafiltration; VSEP, vibration shear enhanced process.

∗ Corresponding author at: Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, Malaysia. Tel.: +60 3 89466304; fax: +60 3 86567120. E-mail address: fakhrul@eng.upm.edu.my (A. Fakhru’l-Razi).

1.5.3. Treating chemicals535
1.5.4. Heavy metals535
1.5.5. Radionuclides535
2. Produced water management535
2.1. Physical treatment535
2.1.1. Adsorption of dissolved organics on activated carbon, organoclay, copolymers, zeolite, resins535
2.1.2. Sand filters537
2.1.3. Cyclones537
2.1.4. Evaporation538
2.1.5. Dissolved air precipitation (DAP)538
2.1.6. C-TOUR538
2.1.7. Freeze–thaw/evaporation538
2.1.8. Electrodialysis (ED)538
2.2. Chemical treatment538
2.2.1. Chemical precipitation538
2.2.2. Chemical oxidation538
2.2.3. Electrochemical process538
2.2.4. Photocatalytic treatment538
2.2.5. Fenton process539
2.2.6. Treatment with ozone539
2.2.7. Room temperature ionic liquids539
2.2.8. Demulsifier539
2.3. Biological treatment539
2.4. Membrane treatment540
2.4.1. Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) membranes540
2.4.2. Bentonite clay and zeolite membrane542
2.4.3. Combined systems542
2.4.4. Modified membrane systems to reduce fouling544
3. Performance evaluation and analysis of treatment technology546
4. Produced water treatment cost evaluation546
5. Discussion and future developments546
5.1. Source of produced water and concentration of pollutants546
5.2. Final requirements for discharge, recycle or reuse546
6. Conclusions548
References548

A. Fakhru’l-Razi et al. / Journal of Hazardous Materials 170 (2009) 530–551 531

1. Introduction

The significance of oil and natural gas in modern civilization is well known. Nevertheless, like most production activities, oil and gas production processes generate large volumes of liquid waste. Oilfield wastewater or produced water contains various organic andinorganiccomponents.Dischargingproducedwatercanpollute surface and underground water and soil.

The permitted oil and grease (O&G) limits for treated produced water discharge offshore in Australia are 30mg/L (milligram per liter) daily average and 50mg/L instantaneous [1]. Based on United States Environmental Protection Agency (USEPA) regulations, the daily maximum limit for O&G is 42mg/L and the monthly average limit is 29mg/L [2]. As regards the significant matter of environmentalconcern,manycountrieshaveimplementedmorestringent regulatory standards for discharging produced water. The monthly average limits of O&G discharge and chemical oxygen demand (COD) prescribed by the Peoples Republic of China are 10 and 100mg/L, respectively [3]. Based on the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR Convention), the annual average limit for discharge of dispersed oil for produced water into the sea is 40mg/L [4]. On the other hand, because large volumes of produced water are being generated, many countries with oilfields, which are also generally water-stressedcountries,areincreasinglyfocusingoneffortstofind efficient and cost-effective treatment methods to remove pollutants as a way to supplement their limited fresh water resources. Reuse and recycling of produced water include underground injection to increase oil production, use for irrigation, livestock or wildlife watering and habitats, and various industrial uses (e.g., dust control, vehicle washing, power plant makeup water, and fire control) [5].

In order to meet environmental regulations as well as reuse and recycling of produced water, many researchers have focused on treating oily saline produced water. Oil content and salinity of produced water from offshore and onshore activities can be reduced through various physical, chemical, and biological methods. In offshore extraction facilities due to space constraints, compact physical and chemical treatment technologies are preferred. However, as capital cost of physical methods and cost of chemicals for chemical treatment of hazardous sludge is high, the application of these methods is limited. Current methods cannot remove minute suspended oil and/or hazardous dissolved organic and inorganic components. On the other hand, biological treatment is a cost-effective method for removing dissolved and suspendedcompoundsfromoilfieldwastewaterinonshoreextraction facilities. The main purpose of this review is:

(a) To introduce oil and gas produced water origin and characteristics, (b) To summarize current technologies available to treat offshore and onshore produced water, (c) To focus on combined methods to improve effluent characteristics, (d) To discuss advantages and drawbacks of the various treatment methods, and

532 A. Fakhru’l-Razi et al. / Journal of Hazardous Materials 170 (2009) 530–551

(e) Discussfuturedevelopmentneedstomeetdischarge,reuse,and recycle standards.

Naturally occurring rocks, in subsurface formations are generally permeated by different underground fluids such as oil, gas, andsalinewater.Beforetrappinghydrocarboncompoundsinrocks, they were saturated with saline water. Hydrocarbons with lower density migrated to trap locations and displaced some of the saline water from the formation. Finally, reservoir rocks absorbed saline water and hydrocarbons (oil and gas). There are three sources of saline water:

• Flow from above or below the hydrocarbon zone, • Flow from within the hydrocarbon zone,

• Flowfrominjectedfluidsandadditivesresultingfromproduction activities.

The last category is called “connote water” or “formation water” andbecomesproducedwaterwhensalinewatermixedwithhydrocarbons comes to the surface [5].

In oil and gas production activities, additional water is injected intothereservoirtosustainthepressureandachievegreaterrecovery levels. Both formation water and injected water are produced along with hydrocarbon mixture. At the surface, processes are used to separate hydrocarbons from the produced fluid or produced water [6].

1.2. Global onshore and offshore produced water production

Global produced water production is estimated at around 250 million barrels per day compared with around 80 million barrels per day of oil. As a result, water to oil ratio is around 3:1 that is to say water cut is 70%. The global water cut has risen since a decade ago and continues to rise. Produced water is driven up by maturing of old fields but driven down by better management methods and the introduction of new oil fields [7,8].

Fig. 1 gives an estimate of onshore and offshore produced water production since 1990, and forecast in 2015.

1.3. Factors affecting production volume of produced water

ReynoldsandKiker[9]evaluateddifferentfactorsthatcanaffect the amount of produced water production on the life of a well:

1. Methodofwelldrilling:ahorizontalwellcanproduceatahigher rate than a vertical well at similar drawdown, or can produce similar production rate at lower drawdown. 2. Location of well within homogeneous or heterogeneous reservoirs: for homogeneous reservoirs, use of horizontal wells reduces water production but in homogeneous reservoirs, the increase in production of horizontal versus unstimulated vertical wells is proportional to the reservoir’s area contacted by the wells. 3. Different types of completion: the open hole method permits testing of drilling zones and avoids drilling into water. On the other hand, the perforated completion method offers a much higher degree of control since the interval can be perforated and tested. 4. Single zone and commingled: most wells are initially completed in a single zone. As oil rate declines because of maturing of the well, other zones may be opened to maintain the oil production rate, as a result water production too increases. 5. Type of water separation technologies: different methods are used to reduce costs of lifting and/or water handling for wells that produce large quantities of saline water. These methods are water shut-off treatment using gelled polymers, reducing beam pump lifting costs, power options to reduce electrical costs and separation technologies. 6. Waterinjectionorwaterfloodingforenhancingoilrecovery:the aim of water flooding is getting the well-treated water to the oil level to increase production rate. Because of water flooding, an increasingly higher percentage of water is produced. As a flood progresses, the volume of required water for injection increases. In this case, makeup water with suitable chemical characteristics is necessary. The poor quality of treated produced water, or makeup enables sealing, clay swelling, and brine incompatibilities. 7. Poor mechanical integrity: many water entries are caused by mechanical problems of the casting holes caused by corrosion or wear, and splits caused by flows; excessive pressure can allow unwanted reservoir fluids to enter the casing and increase water production. 8. Underground communications: underground communications problems happen near wellbores or reservoirs. Both these problems generate increase in produced water. Near wellbore problems are the channels behind casing, barrier breakdowns, and completions into or near water. Reservoirrelated problems are coning, cresting, channeling through higher permeability zones or fractures, and fracturing out of zone.

Fig. 1. Global onshore and offshore water production. Reprinted with permission from Ref. [7].

A. Fakhru’l-Razi et al. / Journal of Hazardous Materials 170 (2009) 530–551 533 1.4. Characteristics of produced water

Produced water is a mixture of organic and inorganic materials.

Some factors such as geological location of the field, its geological formation, lifetime of its reservoirs, and type of hydrocarbon product being produced affect the physical and chemical properties of produced water [5].

Produced waters characteristics depend on the nature of the producing/storage formation from which they are withdrawn, the operationalconditions,andchemicalsusedinprocessfacilities.The composition of produced water from different sources can vary by order of magnitude. However, produced water composition is qualitatively similar to oil and/or gas production [10]. The major compounds of produced water include:

(A) Dissolved and dispersed oil compounds, (B) Dissolved formation minerals, (C) Production chemical compounds, (D) Production solids (including formation solids, corrosion and scale products, bacteria, waxes, and asphaltenes), (E) Dissolved gases [1].

Oil is a mixture of hydrocarbons including benzene, toluene, ethylbenzene, and xylenes (BTEX), naphthalene, phenantherene, dibenzothiophene (NPD), polyaromatic hydrocarbons (PAHs) and phenols. Water cannot dissolve all hydrocarbons, so most of the oil is dispersed in water [6].

Theamountsofdissolvedandsuspendedoilpresentinproduced water (prior to treatment) are related to following factors:

• Oil composition, • pH, salinity, TDS (total dissolved solids), temperature,

• Oil/water ratio,

• Type and quantity of oilfield chemicals,

• Type and quantity of various stability compounds (waxes, asphaltenes, fine solids) [1].

1.4.1.1. Dissolved oil. The water-soluble organic compounds in produced water are polar constituents and found distributed between the low and medium carbon ranges. Organic acids such as formic acid and propionic acid are typically in produced water. pH and temperature increase soluble organics in produced water. Pressure enhances dissolved organic compound concentration slightly. Temperature alters the relative ratio of carbon ranges within the water. Soluble compounds do not increase total dissolved organics in produced water. In addition, salinity does not significantly affect the dissolved organics in produced water [12]. The amounts of oil soluble in produced water depend on type of oil, volume of water production, artificial life technique, and age of production [13]. Aromatic compounds which are the most important chemicals contributing to natural environments toxicity cannot be removed efficiently by oil/water separation techniques. Besides, by increasing alkylation of components, the concentration of naphthalene, phenantherene, dibenzothiophene and their C1–C3 alkyl homologous and alkylated phenols reduces [14]. In some sites, concentrations of these components are relatively high [15]. BTEX and phenols are the most soluble compounds in produced water [6]. Aliphatic hydrocarbons, phenols, carboxylic acid, and lowmolecular weight aromatic compounds are included as soluble oil compounds in produced water [13].

1.4.1.2. Dispersed oil. Dispersed oil consists of small droplets of oil suspended in the produced water. The amount of dispersed oil in produced water depends on the density of oil, the shear history of the droplet, the amount of oil precipitation and interfacial tension between the water and oil [13]. PAHs and some of the heavier alkyl phenols are less soluble in produced water and are present as dispersed oil [6]. The concentration of PAHs and C6–C9 alkylated phenols is strongly correlated to dispersed oil content of produced water [16].

1.4.2. Dissolved formation minerals

Inorganic dissolved compounds in produced water include anions and cations, heavy metals, and radioactive materials. Produced water contains a wide range of both cations and anions. All of them have similar patterns of concentration for different metals [16].

duced water chemistry in terms of buffering capacity, salinity, and scalepotential[1].Salinityisduetodissolvedsodiumandchloride andislesscontributedbycalcium,magnesium,andpotassium.Salt concentrationofproducedwatermayvaryfromafewpartspermillion (ppm) to about 300,000mg/L [1,17], 1000–250,000mg/L [18]. Sulfate concentration in produced water is lower than seawater. In some sites that use seawater for oil enhancing recovery, sulfate concentration is high [1].

1.4.2.2. Heavy metals. Heavy metal concentrations in produced water depend on age of the wells and formation geology [19].P roduced water contains trace quantities of various heavy metals such as cadmium, chromium, copper, lead, mercury, nickel, silver, and zinc [1].

1.4.2.3. Naturally occurring radioactive materials (NORM). The source of radioactivity in scale is from radioactive ions, primarily radium that is co-precipitated from produced water along with other types of scales. Barium sulfate is the most common scale co-precipitated [13]. 226Radium and 228radium are the most abundant NORM in produced water [19]. There is a strong correlation between concentrations of barium and radium isotopes [20].I nt he North Sea, concentrations of 226Ra and 228Ra in samples ranged from below the detectable detection limits 0.3–1.3 becquerel per liter (Bq/L) up to 16 and 21Bq/L, respectively [21].

1.4.3. Production chemical components

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