Article Summary
Onshore produced water treatment requires more than selecting a single separator or filter. Water composition, oil droplet size, suspended solids, flow rate, available pressure, equipment footprint, and the intended destination of the treated water all influence the appropriate treatment train.
By characterizing the produced water and matching primary separation, flotation, and tertiary filtration technologies to the required effluent quality, operators can improve treatment reliability while reducing fouling, excessive backwashing, and downstream equipment problems.
What Is Produced Water Treatment?
Produced water is water brought to the surface during oil and gas extraction. It may include formation water naturally present underground, injected water used during production, and water mixed with hydrocarbons, sand, treatment chemicals, salts, and other constituents.
For upstream oil and gas operations, produced water treatment removes oil, suspended solids, and other contaminants before the water is disposed of, reinjected, discharged, or reused. The required treatment depends on both the incoming water and its intended destination.
Why Onshore Produced Water Is Difficult to Treat
Produced water does not have one standard composition. Conditions vary among fields, wells, formations, production methods, and stages of field life.
Produced Water Chemistry Changes by Formation and Production Stage
Water chemistry and volume can change as a well matures. Systems designed around initial conditions may become undersized or poorly matched as water production increases or contaminant concentrations shift.
Sampling should represent normal operations, production peaks, well changes, chemical treatments, and other conditions likely to affect system performance.
Free, Dispersed, and Emulsified Oil Require Different Treatment Approaches
Large free-oil droplets are generally easier to separate than small dispersed droplets. Stable emulsions can be more difficult because the oil remains distributed throughout the water.
Droplet size, density difference, viscosity, temperature, and chemical conditions influence how readily oil separates. These factors affect whether gravity separation, hydrocyclones, flotation, filtration, or a combination is appropriate.
Sand and Suspended Solids Can Damage Downstream Equipment
Sand and solids can erode equipment, plug internals, accumulate in vessels, and increase filter loading. Effective solids management upstream can improve the reliability of flotation and tertiary filtration.
Disposal, Reinjection, and Reuse Require Different Water Quality
Water sent for disposal may have different specifications than water used for reinjection or beneficial reuse. Reinjection requirements may be driven by oil content, solids concentration, particle size, and the risk of formation plugging.
Reuse can require additional treatment for dissolved contaminants, salinity, organics, or microorganisms. The final water-quality target should be defined before selecting equipment.
How to Characterize Produced Water Before Selecting Equipment
A produced water study should document average and peak flow, pressure, temperature, oil concentration, droplet size distribution, suspended solids, particle size, salinity, and relevant dissolved contaminants.
Operators should also evaluate chemical additives, emulsion stability, expected production changes, available utilities, and space limitations. Representative data is essential because a treatment train designed around an incomplete sample may perform poorly when actual conditions change.
How an Onshore Produced Water Treatment Train Works
An effective treatment train typically removes contaminants in stages. Each stage reduces the burden on the equipment that follows.
Primary Produced Water Treatment Removes Bulk Oil and Solids
Primary separation removes larger oil droplets, free oil, and bulk solids before finer treatment.
Using Deoiling Hydrocyclones for Compact Oil-Water Separation
Deoiling hydrocyclones use centrifugal force and density differences to separate oil from water. Produced water enters the cyclone tangentially, creating a spinning flow that directs the denser water outward while the less-dense oil moves toward the center.
Performance depends on droplet size, density difference, fluid viscosity, centrifugal force, and the distance the oil must travel. Hydrocyclones can be useful where operators need compact, continuous separation and sufficient pressure is available.
Secondary Produced Water Treatment Removes Dispersed Oil
Flotation systems introduce gas bubbles that attach to oil droplets and solids, carrying them to the surface for removal.
Using Compact Flotation Units Where Space Is Limited
Compact flotation units combine cyclonic and flotation principles to remove oil and solids. They are available in single- or multiple-stage arrangements and can be adapted to different process conditions.
For onshore facilities with limited space, a compact configuration can provide secondary treatment without the footprint of a larger conventional flotation vessel.
Using Induced Gas Flotation for Oil and Fine Solids Removal
Induced gas flotation systems introduce gas into the water through mechanical or hydraulic methods. Gas bubbles attach to oil droplets and solids, creating a surface layer that can be removed.
IGF systems should be evaluated according to flow, contaminant loading, residence time, chemical conditioning, maintenance needs, and available footprint.
When Dissolved Gas Flotation Is Appropriate
Dissolved gas flotation generates microbubbles by saturating a pressurized stream of treated water with gas and then releasing it into the flotation chamber. The bubbles lift oil and solids to the surface for skimming.
The difference between IGF and DGF is primarily how the bubbles are produced and introduced. Selection should be based on water characteristics, removal requirements, operating pressure, footprint, and system complexity.
Tertiary Produced Water Treatment Provides Final Polishing
Filtration is used downstream of separation and flotation when lower residual oil or solids concentrations are required.
Using Walnut Shell Filters for Residual Oil Removal
Walnut shell filtration is used as a tertiary treatment for low concentrations of fine free-oil droplets and solids. These filters are commonly installed downstream of hydrocyclones or flotation systems before disposal or reinjection.
Walnut shell filters can suit remote onshore fields because the media is relatively inexpensive and the systems require limited operator intervention. However, their size, weight, and backwash infrastructure must be considered.
Using Multimedia Filtration for Suspended Solids Control
Multimedia filtration for produced water removes sediment and particulates by passing pressurized water through layers of filtration media. As solids accumulate, pressure drop increases and the system must be backwashed.
These systems can provide final wastewater filtration or pretreatment for more advanced processes, but backwash volume, waste handling, and differential-pressure monitoring must be included in the design.
How to Select Produced Water Treatment Technologies
Technology selection should begin with the required outlet quality and then work backward through the treatment train.
Operators should compare:
Normal and peak inlet conditions
Oil droplet and particle sizes
Available footprint and pressure
Chemical and energy use
Backwashing and waste volumes
Inspection and maintenance access
Sensitivity to flow or chemistry changes
Expected future water production
A treatment train that performs well at current conditions may become unreliable if future water volumes or contaminant loads are ignored.
Selecting Treatment for Disposal, Reinjection, or Reuse
Disposal may require oil and solids removal to meet facility or regulatory requirements. Reinjection generally requires tighter solids and oil control to reduce plugging and preserve injectivity. Beneficial reuse may require additional treatment for dissolved substances or other application-specific concerns.
This is why onshore industrial wastewater treatment should be designed around the complete water-management objective rather than one isolated piece of equipment.
Common Produced Water Treatment Problems and Their Causes
High oil levels after separation can result from droplets that are too small, changing chemistry, inadequate residence time, or unstable flow. Frequent filter backwashing may indicate excessive upstream solids or oil loading. Declining performance can also result from worn internals, improper chemical conditioning, or inlet conditions that no longer match the original design.
A recurring downstream problem often points to an upstream process limitation.
Common Mistakes When Selecting a Produced Water Treatment System
Common mistakes include relying on one water sample, overlooking peak flow, selecting filtration without adequate upstream oil removal, and comparing equipment only by capital cost. Operators may also underestimate backwash storage, waste disposal, controls, chemical use, and maintenance access.
The most reliable systems treat produced water separation and filtration as an integrated process.
Building a Reliable Onshore Produced Water Treatment Strategy
Reliable treatment starts with representative water data, a defined outlet specification, and a realistic understanding of future operating conditions. Primary separation, flotation, and filtration should work together so each stage protects the next.
CECO’s engineered produced water treatment systems support onshore industrial applications with compact separation, flotation, filtration, and packaged treatment technologies.
Frequently Asked Questions
What Contaminants Are Found in Produced Water?
Produced water may contain free and dispersed oil, suspended solids, sand, dissolved salts, metals, organic compounds, treatment chemicals, and microorganisms. Composition varies by formation and production conditions.
What Is the Best Way to Remove Oil From Produced Water?
The appropriate method depends on oil concentration, droplet size, emulsion stability, flow, pressure, and outlet requirements. Treatment may combine hydrocyclones, flotation, and tertiary filtration.
How Do Deoiling Hydrocyclones Work?
Hydrocyclones use centrifugal force and density differences to direct denser water toward the outside of the cyclone while concentrating less-dense oil near the center.
What Is the Difference Between Induced Gas and Dissolved Gas Flotation?
IGF introduces gas through mechanical or hydraulic methods. DGF dissolves gas into a pressurized water stream and releases it to generate microbubbles.
When Are Walnut Shell Filters Used in Produced Water Treatment?
They are typically used downstream of hydrocyclones or flotation units to polish low concentrations of residual oil and fine solids before disposal or reinjection.
Can Produced Water Be Treated for Reuse?
Yes, but the treatment required depends on the reuse application and may extend beyond oil and solids removal. Operators can review a produced water treatment case study to explore CECO’s related capabilities.
How Do You Select an Onshore Produced Water Treatment System?
Selection requires representative water characterization, a defined outlet specification, and evaluation of flow, pressure, footprint, maintenance, utilities, and future production. To assess the right separation and filtration treatment train for a specific application, contact CECO for professional guidance and assistance.
