Protect Disposal Wells, Optimize Capacity, and Reduce Disposal Costs

Solutions for disposal well plugging and volume reduction

April 5th 2021

Key Takeaways

  • Disposal wells are an established method for disposing of hazardous fluids by injecting them deep underground.
  • Commingling (mixing) incompatible fluids in a disposal well may inadvertently cause solids to precipitate, which risks plugging the well or underground formation.
  • Plugging is disruptive and costly to fix, but operators can prevent it with advanced sensors, controls, and targeted wastewater treatment.
  • Disposal well capacity is limited in some areas, new wells can be costly to install, and permitting may be challenging. Reducing wastewater volume prior to injection helps mitigate risks while maximizing existing disposal well capacity.
  • Reducing wastewater volume also reduces water transport costs, often a significant part of overall disposal costs.
  • Volume reduction can be achieved incrementally to balance wastewater treatment economics vs. disposal costs.
  • For many disposal well operators and their customers, the best first step towards managing costs is a thorough economic options analysis, evaluating a broad suite of water treatment technologies.

Disposal Wells Overview

Disposal wells, or deep injection wells, are used by many industries to dispose of hazardous wastewater underground. Most produced water from onshore oil & gas is sent to disposal wells. They are also used by the chemical manufacturing, refining, and food and beverage industries. There are thousands of disposal wells in North America alone.

 

Wastewaters sent to disposal wells are generally highly impaired and uneconomic to dispose of by any other means. They often contain high levels of total dissolved solids (TDS), scaling ions, hydrocarbons, heavy metals, or other contaminants.

 

Important considerations for the disposal well industry include meeting safety and environmental regulations, maximizing available pressure and volume capacity, and preventing the plugging of wells by precipitated solids. Customers that use disposal wells are concerned with cost and environmental impacts associated with disposal. Saltworks can help with these challenges.

Barium Sulfate Solids
Solid, insoluble barium sulfate
Disposal Well Plugged Pipework
Pipework plugged with water insoluble solids

Protection from Precipitation & Plugging

Commingling in a disposal well is when two different wastewater streams are allowed to mix. Depending on their dissolved ion chemistry, a water-insoluble solid may precipitate. A common example is the commingling of sulfate- and barium-rich waters which produces solid barium sulfate. Commingling in disposal wells carries the risk of plugging, which is highly disruptive to disposal well operation and expensive to rectify.

 

Fortunately, operators have an option to prevent plugging. A real-time ion sensor compatible with highly impaired wastewaters, such as Saltworks’ ScaleSense, can screen incoming flows for incompatible ions. For example, identifying and segregating high barium waters from high sulfate waters, preventing accidental formation of barium sulfate plugs. Controls integrating such a sensor can divert a flow to a separate stream, which can be disposed of or treated inexpensively, for example with an automated chemical treatment system such as BrineRefine, which makes the water chemistry safe to commingle.

Sensor protecting disposal wells from plugging
A control using a ScaleSense analyzer prevents plugging by stopping the commingling of incompatible fluids
Treating disposal well waters before injection to protect from plugging
A targeted chemical treatment process precipitates ions-of-concern before water injection, preventing plugging

It Pays to Reduce Volume

Reducing wastewater volume, both at the site of generation as well as at the injection site, benefits both disposal well operators and customers alike. Operators can maximize disposal pressure and capacity, which is especially important in disposal constrained areas such as the Marcellus or West Montney shale basins. Less overall volume also means that operators realize reduced seismic and cross-contamination risk, which reduces the possibility of curtailment.

 

For customers, wastewater transport can represent a significant portion, or even the majority, of wastewater management costs. Less volume means lower trucking costs, along with reduced emissions, impacts on roads, and potential spills. Another benefit is that freshwater can be recovered for reuse, depending on the wastewater chemistry.

Barium Sulfate Reaction
Barium sulfate precipitation reaction
BrineRefine Chemical Softening System
BrineRefine, an automated chemical treatment system

Volume Reduction Techniques

Volume reduction technologies come in many shapes and sizes and can be combined with custom process engineering to provide a solution to suit specific wastewaters.

 

Membrane systems are usually the most cost-effective at volume reduction: nanofiltration (NF), reverse osmosis (RO), and ultra high-pressure reverse osmosis (UHP RO) provide increasing volume reduction. All produce a concentrated liquid brine reject. More advanced systems, such as Saltworks’ XtremeRO/NF can achieve reduction and reliability on challenging fluids, such as those with scaling ions and organics, however total dissolved solids (TDS) need to be below 90,000 mg/L for RO systems to be applicable.

 

When further reduction is required, or when TDS is greater than 90,000 mg/L, thermal evaporator-crystallizers are available to squeeze wastewater volumes even further. Thermal systems are more energy intensive than membrane systems, and achieving zero liquid discharge can be challenging for highly impaired wastewaters. Saltworks’ SaltMaker MultiEffect is an example of a modernized evaporator-crystallizer providing reliable solids production, and available in several options to meet energy, chemistry, and capacity requirements. Some wastewaters have volatile organic compounds (VOCs). An air-safe evaporator, such as the SaltMaker AirBreather, can ensure air emission standards are met.

 

Thermal systems generally have higher total cost than membrane systems, so it is advantageous to maximize membrane volume reduction first, to reduce the size of downstream thermal systems. Volume reduction can also be achieved incrementally, only taking the next process step if warranted by the treatment economics. In some cases, if water chemistry is suitable, ultrahigh recoveries could be achievable with membrane systems, which would reduce volumes needing disposal or going to an evaporation pond, eliminating the need for a thermal system.

AirBreather Evaporator Crystallizer Effect
A SaltMaker AirBreather evaporator module, employed in volume reduction.

How Saltworks Can Help

For disposal well operators and customers the best first step towards lowering costs, extending the utility of well assets, or achieving water reuse targets is a thorough options analysis. This should include understanding the specific water chemistry, evaluating a broad range of water treatment technologies, economic modelling, and assessing regulatory and environmental impacts.

 

Saltworks’ water experts can help you understand your treatment and disposal options. Our product range includes advanced sensors, chemical treatment, membrane, and thermal systems so we can develop the optimal solution for your project. Send us your project details to get started.

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