Frac & Shale Produced Water Management,
Treatment Costs & Options
25 October 2019
- Economic shale produced water management strategies require you to explore: treatment options, treatment costs compared to disposal costs, and methods to manage risk.
- Open-to-atmosphere evaporators offer the best economics for shale volume reduction, although it is important to ensure that: your emissions of volatile organic compounds (VOCs) are managed, a low cost heat source is available, your permit will allow it, and sufficient water volume removal can be achieved for minimal liquid discharge (MLD) or zero liquid discharge (ZLD).
- New advanced membrane systems may be economic for shale produced water volume reduction with the TDS is lower than 80,000 mg/L.
Source Water and Disposal Costs in Shale
Shale Water Treatment Options
In general, there are three categories for treatment:
Particulate & Hardness Removal: ($)
- Water hardness is removed by chemical softening and particulates are removed by bag filters. New developments in chemical softening system design remove pains of the past, such as over or under dosing, poor control, large physical footprint and lack of modularity.
- Dosing: Conventional chemical softening systems use set dosing rates, which result in poor precision on constantly changing shale waters. This can lead to underdosing, which may cause scale, or overdosing, which results in wasted chemicals and increased operating costs. Modern chemical softening systems that use sensor-driven precision dosing avoid these problems by reducing waste and maintaining treatment system performance.
- Filter Quality: Some bag filter systems are treated as disposable, resulting in higher waste, higher manual handling, and greater disposal costs. Opting for re-usable, highly robust filters with a semi-automated solids handling system can reduce these costs, and improve both the operability and environmental footprint of your particulate removal program.
- Intervention: Whether dealing with bag filters or chemical softening, conventional systems can require high operator intervention. New technologies, such as our BrineRefine platform, come as a packaged, automated system that reduces intervention and improves the economics of this water treatment process.
Volume Reduction: ($$)
- Open to Atmosphere Evaporators: Evaporation to atmosphere will reduce produced water volumes at a lower cost than closed evaporators (discussed later in this article). However, their fit with respect to thermal needs, air emissions, reject concentration, and permitting must be confirmed. Total cost of ownership (capital cost + operating costs) may range from $12-$24/m3 ($2-$4/BBL).
- Air Emissions: Although water vapour is harmless to the environment, produced water may include volatile organic compounds (VOC) that evaporate with the water. Benzene is the most common VOC in produced water and is a regulated carcinogen. There are also volatile forms of arsenic and radium that exist as a part of organic complexes. Make sure you plan ahead for VOC management, since regulators and stakeholders will expect it. Open to Atmosphere Evaporators have been procured and then rapidly shut down due to stakeholder concerns. Invest in risk management and possibly a pilot project prior to making a large capital purchase. Saltworks’ open-to-atmosphere evaporator, AirBreather, includes a novel VOC management system that removes VOCs from the exhausted water vapor. Pilot plants are available to prove this and can be complemented with air dispersion modeling to support permitting discussions.
- Energy: One cubic meter (6.3 BBL) of water requires 3.3 GJ (2.2 million BTUs) of energy to evaporate. However, the value of energy, known as ‘exergy’, depends on its temperature. It may only make sense to spend this energy if a waste heat source or a low temperature heat source is available, such as waste heat from reciprocating engine jacket cooling, exhaust, or waste gas that is flared. Water boils at 100 °C (212 °F), and most engine waste heat sources are 85-95 °C, which is not sufficient to evaporate water. However, the Saltworks’ AirBreather does not involve boiling water, instead it humidifies air. This enables the use of a much lower temperature heat source, whereas other open-to-atmosphere evaporators use submerged combustion with direct-fired gas sources, such as natural gas. There is a trade-off in that humidifying air requires larger chambers, but they operate at a lower temperature and can be constructed from engineered plastics to withstand corrosion and scaling issues.
- Pre-treatment: Some evaporators cannot tolerate scale-causing compounds, so be sure to complete a water analysis and check with the technology vendor. The AirBreather was developed to accept any fluid without pre-treatment, and remove scale by self-cleaning before it becomes irreversible.
- Concentration limits: Most open evaporators are limited to an upper TDS concentration of 150,000 to 250,000 mg/L, where they may start plugging with accumulated low solubility solids. It is worth determining these concentration limits before investing, since they directly impact the plant capacity. If you start with a TDS of 200,000 mg/L and can only concentrate to 250,000 mg/L this means a volume reduction of 20% will be achieved – contact us for help with making these calculations for your project. The AirBreather has no TDS limit, and can make solids due to its built-in self-cleaning and corrosion-proof construction. This means you can squeeze almost all the produced water, reducing your volume to any desired level. However, recall that rejected residual TDS waste must be managed.
- Corrosion: After scale, corrosion is the second greatest killer of evaporators. Stainless steel will rapidly corrode when exposed to high chloride concentrations in produced waters. Super duplex stainless steel variants offer increased resistance, but they can cost more than exotic metals, such as titanium and Hastelloy, which do not corrode. The AirBreather’s wetted parts are 95% gel-coated fiberglass and engineered plastic to entirely remove the corrosion risk. Heat exchangers are constructed with titanium but no boiling occurs on any metal surfaces, limiting scale potential. The AirBreather’s intelligent controls monitor heat exchanger performance and clean them in an automated manner before any irreversible performance degradation occurs.
Fresh Water Production: ($$ to $$$)
- Membranes ($): Reverse osmosis (RO) and electrodialysis reversal (EDR) are the most widely used membrane desalination technologies. However, these methods offer limited economic fit to water with mid-range TDS concentrations (less than 40,000 mg/L). New advancements in membrane systems, such as Extreme Reverse Osmosis, can now be economic with TDS up to 80,000 mg/L. The Extreme RO systems can concentrate produced water up to 140,000 mg/L TDS, reducing disposal volumes for minimal liquid discharge (MLD). Membrane system total cost of ownership (capital cost + operating costs) may range from $3-$9/m($0.5-$1.5/BBL), however, pre-treatment, such as BrineRefine, could change this cost equation.
- Closed Evaporative Crystallizers ($): Closed evaporative crystallizers can offer applicability across a wide range of TDS concentrations, but they are also the most expensive treatment option due to their size and complexity. Closed systems condense water vapor and employ different methods to recycle a portion of the thermal energy or heat of condensation. This lowers their energy consumption relative to open to atmosphere evaporators but increases their relative cost.
- When considering a closed evaporative crystallizer, you should also factor in: pre-treatment for scaling, concentration limits of conventional evaporators, and corrosion risk. In addition, if freshwater is produced, it must either be stored, re-used, or released to the environment. One advantage of freshwater storage and transportation over produced water storage is that it requires less containment. Although you should check your local regulations, in many cases, freshwater may be stored in ponds, industrial water bags, or tanks and transported via a lower cost lay flat hose. Freshwater may be used by a neighboring agriculture facility or can also be discharged to the environment in some jurisdictions, noting that environmental discharge permitting in the US may take up to a year and the permit is typically only valid for a single site. These added dimensions speak to why open-to-atmosphere evaporators can be a better option if air emissions are managed and thermal energy is available.
- Closed evaporative crystallizer total cost of ownership (capital cost + operating cost) may range from $24-$48/m3 ($4-$8/BBL), making them the most expensive treatment option.
Logistics and Residual Reject Disposal
Logistics: Logistics and water hauling can dominate shale water management costs if a disposal outlet is not nearby. When assessing treatment and disposal options keep an understanding of logistics cost in mind, including wait times for trucks to load and unload. As a rule of thumb, it may cost $15/m3 ($94/BBL) per hour of transport once loading and unloading times are factored in. Costs also vary depending on the quality of roads in the area. It can make sense to review pre-concentration prior to transport, which lowers the volumes of the water being hauled. In many cases, there will be an economic optimum that combines re-use, storage, treatment, and transport for final reject waste disposal.
For example, if transport and disposal is $30/m3, and volumes can be halved for $10/m3, and solids produced afterwards for $45/m3, then it may make the most sense to pre-concentrate and halve the volumes for $10/m3 followed by transport and disposal for $30/m3. The net blended cost will be $20/m3. Preferably, the reject waste is as concentrated as possible until it reaches a cost that is just below the transport-disposal costs. It is important to note that as produced water is concentrated and its volume reduced, it can become denser with more scaling potential. Higher density waters can be beneficial for disposal wells; however, scaling waters may plug them. Technologies, such as BrineRefine, are available to reduce the scaling potential of highly concentrated brines prior to disposal, and thereby protect the disposal well asset from scaling and plugging while maintaining the beneficially high density.
Residual Reject Disposal: Although relatively pure water can be separated from produced waters, reject residual waste is always left behind. This will include organics (petroleum byproducts) and inorganics (mixed salt). It is important to plan for this in advance. One advantage of disposal wells is that they dispose of all residuals, and as noted above, disposal costs and volume can be limited through treatments that pre-concentrate. However, it is also possible to: (a) produce a mixed solid waste for landfill disposal; and (b) separate out the organic phase and produce refined salts for industrial re-use. This includes a combination of chemical pretreatment and staged crystallization.
Be sure to study and assess the lifetime of disposal options, if solids are going to be produced. Landfill waste must pass paint filter, leaching (TCLP) and radioactivity tests. Saltworks can help assess if your produced water may pass these tests through bench testing. Saltworks can also review your water’s potential to produce beneficial industrial salt for re-use – although this is unlikely to offer a secondary revenue stream through salt sales. Most salts are of low value and the costs of producing, handling and transport barely offset any revenue generated. However, industrial re-use offsets costs by avoiding the need to pay for landfill disposal.
Shale gas and oil production presents a leading energy source moving forward, yet its future and production is tightly linked to water management. Every water type, job site, and economic case is different. Contact us to review your specific situation, benefit from our expertise, and assess if your water management costs or risks can be lowered.