What Is Produced Water?

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When drilling and production operations are going on, produced water is the one that is obtained from underground formations with oil and natural gas. It comes from porous rock reservoirs with hydrocarbon resources. Consequently, more of this “formation water” will be produced as time goes by when wells deplete oil and gas. Produced water is a significant industry waste stream responsible for 240 million barrels per day worldwide. It includes different impurities such as salts, oils, and chemicals that makes it an environmentally dangerous wastewater necessitating adequate treatment and management to allow secure disposal or reuse.

In the oil and gas industry, water is an ever-present companion to the hydrocarbons being extracted from reservoirs. This water, known as “produced water,” is generated during the production of oil and natural gas from underground formations. As drilling and extraction activities progress, increasing volumes of produced water are brought to the surface along with the desired oil and gas resources.

Produced water is one of the largest waste streams in the exploration and production sector, posing significant environmental challenges as well as financial burdens for operators. Proper management and treatment of this wastewater are crucial for minimizing environmental impacts, meeting regulatory standards, and enabling beneficial reuse or disposal options.

In this article, we will take an in-depth look at produced water, its characteristics, composition, volumes generated, associated environmental concerns, and available treatment and management strategies employed by the industry.

What Causes Produced Water?

Produced water originates from the same underground formations that contain oil and gas reserves. Over millions of years, these porous rock formations have become saturated with water, known as “formation water.” This water has been trapped alongside the hydrocarbons under immense pressure, measured using a pressure sensor.

When wells are drilled into these reservoirs, the reduction in pressure causes both the desired oil and gas resources and the formation water to flow towards the well and travel up to the surface. In fact, for every barrel of oil extracted, there can be several barrels of produced water brought up as well.

The volume of produced water can vary significantly depending on the age, depth, and location of the reservoir, as well as the production phase. Typically, older wells tend to produce higher ratios of water to oil, a phenomenon known as a “high water cut.” This is because over time easy-to-get-at oil and gas are used up, leaving more formation water in the reservoir.

What Is Produced Water Made Of?

Produced water is not simply salty water; it is a complex mixture of various organic and inorganic compounds, some of which can be naturally occurring, while others may be introduced during drilling and production processes. The composition of produced water can vary substantially depending on the geographic location, geological formation characteristics, and the type of hydrocarbon product being extracted.

Salts

Produced water typically has high levels of dissolved salts, such as sodium, potassium, calcium, and magnesium chlorides, contributing to its high salinity and total dissolved solids (TDS) content.

Oil & Grease

Small amounts of dispersed oil and grease can be present in produced water, originating from the reservoir or introduced during production operations.

Organic Compounds

Naturally occurring organic compounds, such as aromatic hydrocarbons, phenols, organic acids, and dissolved organic matter, can be present in produced water.

Heavy Metals

Trace amounts of heavy metals like barium, cadmium, chromium, lead, and mercury may be found in produced water, depending on the geological formation.

Naturally Occurring Radioactive Materials (NORM)

Some produced water can contain low levels of naturally occurring radioactive materials, such as radium, which are brought up from underground formations.

Production Chemicals

Depending on the well treatment and production processes employed, produced water may contain residues of chemicals used for drilling muds, well stimulation, corrosion inhibitors, biocides, or scale inhibitors.

Suspended Solids

Produced water can carry various suspended particles, including clay, silt, and sand from the reservoir formations.

The exact composition and concentration of these components can vary significantly from one well to another, even within the same production field or geographic region. This variability poses challenges for the treatment and management of produced water, as different strategies may be required to address specific contaminants effectively.

Volumes Of Produced Water Generated

The volumes of produced water generated by the oil and gas industry are staggering. According to estimates, global onshore and offshore operations generate approximately 250 million barrels of produced water every day. This immense volume highlights the scale of the water management challenges faced by the industry.

The amount of produced water generated can vary greatly depending on several factors, including:

  • The age of the well – as mentioned earlier, older wells tend to produce higher water-to-oil ratios, leading to increased volumes of produced water over time
  • Reservoir characteristics – the geology and characteristics of the reservoir, such as porosity, permeability, and water saturation, can significantly influence the amount of formation water produced
  • Production techniques – enhanced oil recovery (EOR) methods, such as water flooding or steam injection, can substantially increase the volume of produced water generated
  • Well type – onshore wells typically produce lower volumes of produced water compared to offshore wells, where the water cut can be significantly higher
  • Geographic location – the geology and hydrocarbon reserves in different regions can result in varying amounts of produced water generation

We should mention that in some mature oil and gas fields, the volume of produced water can exceed the volume of oil extracted by a factor of 10 or more. For example, in the United States, it is estimated that the oil and gas industry generates over 20-25 billion barrels of produced water annually, dwarfing the country’s oil production.

Environmental Concerns And Challenges

Produced water poses significant environmental challenges due to its complex composition and potential for contamination. If there is poor environmental management and treatment, produced water can have detrimental impacts on surface water, groundwater, and soil ecosystems.

Surface Water Contamination

Improper discharge of untreated or insufficiently treated produced water into surface water bodies, such as rivers, lakes, or coastal waters, can lead to pollution and harm aquatic life.

Groundwater Contamination

Leaks, spills, or improper disposal of produced water can potentially contaminate groundwater resources, rendering them unsuitable for drinking, irrigation, or other uses.

Soil Contamination & Air Pollution

Land application or accidental releases of produced water can lead to soil contamination, affecting vegetation growth and potentially entering the food chain.

Produced water can contain volatile organic compounds (VOCs) and other air pollutants that can be released into the atmosphere during storage, treatment, or disposal processes.

Toxicity To Aquatic Life

Some components of produced water, such as heavy metals, NORM, and certain organic compounds, can be toxic to aquatic organisms, potentially disrupting ecosystems.

Corrosion & Scaling

The high salinity and presence of certain minerals in produced water can cause corrosion and scaling issues in production equipment, pipelines, and treatment facilities, leading to potential environmental issues and increased maintenance costs.

Effective treatment and responsible management of produced water are crucial to mitigate these environmental concerns and ensure the long-term sustainability of oil and gas operations.

Produced Water Treatment And Management Strategies

Given the significant volumes, complex composition, and environmental challenges associated with produced water, the oil and gas industry employs various treatment and management strategies to handle this waste stream responsibly. 

The choice of treatment methods depends on factors such as the composition of the produced water, regulatory requirements, and the intended reuse or disposal option.

Primary Treatment

Physical separation techniques, such as hydrocyclones, settling tanks, and skim tanks, are used to remove free oil, grease, and larger suspended solids from the produced water.

Secondary Treatment

Biological treatment processes, like activated sludge systems or membrane bioreactors, can be employed to remove organic matter and reduce the biochemical oxygen demand (BOD) of the produced water.

Dissolved air flotation (DAF) or induced gas flotation (IGF) units can further remove suspended solids, dispersed oil, and grease.

Tertiary Treatment

Advanced oxidation processes (AOPs), such as UV/hydrogen peroxide or ozone treatment, can be used to degrade recalcitrant organic compounds and oxidize contaminants.

Membrane filtration technologies, including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), can effectively remove dissolved solids, heavy metals, and other contaminants from produced water.

Ion exchange resins can selectively remove specific ionic species, like heavy metals or hardness ions, from the water.

Thermal Treatment

Evaporation and crystallization processes can concentrate and separate dissolved solids from produced water, allowing for the recovery of high-quality distillate or brine concentrates.

Beneficial Reuse

Treated produced water can be reused for various purposes within the oil and gas operations, such as drilling and fracturing fluids, enhanced oil recovery (EOR) processes, or steam generation for thermal recovery methods.

In some cases, highly treated produced water may be suitable for agricultural or industrial water reuse applications, depending on local regulations and water quality parameter requirements.

Disposal Options

Deep well injection: Produced water can be disposed of by injecting it into deep underground formations, isolated from freshwater aquifers. This method is widely used but carries risks of induced seismicity and potential groundwater contamination if not properly managed.

Evaporation ponds: In arid regions, produced water can be stored in lined evaporation ponds, allowing the water to evaporate while leaving behind concentrated salts and solids, improving pond water quality.

Offshore discharge: In offshore operations, treated produced water may be discharged into the ocean, subject to stringent regulatory limits and monitoring requirements to protect marine ecosystems.

Emerging Technologies

Forward osmosis (FO) and membrane distillation (MD) are promising membrane-based technologies that can potentially treat produced water with lower energy requirements compared to traditional thermal desalination processes.

Electrochemical oxidation processes, like electrocoagulation and electrooxidation, offer alternative methods for removing organic contaminants and heavy metals from produced water.

Adsorption processes using advanced materials, such as graphene-based adsorbents or metal-organic frameworks (MOFs), show potential for selective removal of specific contaminants.

Produced Water Management Challenges

Variations in produced water composition: The great variation in the composition of produced water, even within the same field, results in challenges to design and optimize treatment systems.

Remote locations: Remote areas host many oil and gas operations that make it difficult to convey produced water to centralized treatment facilities, or access specialized equipment.

Changing regulations: Environmental rules governing discharge and disposal of produced water are ever changing with operators necessitated to adjust their management strategies accordingly.

Cost considerations: It can be expensive for small operators or those operating on a limited infrastructure base to treat and manage produced water.

Legacy issues: Proper management of produced water from abandoned or orphaned well sites can be a significant challenge, particularly in regions with a long history of oil and gas production.

Industry Initiatives & Research

Collaborative efforts between the oil and gas industry, academic institutions, and research organizations are ongoing to develop more efficient, cost-effective, and environmentally sustainable produced water treatment technologies.

Research is focused on improving membrane performance, developing advanced oxidation processes, exploring beneficial reuse opportunities, and minimizing the environmental footprint of produced water management.

Industry representatives and partnerships aim to share best practices, promote knowledge transfer, and address regulatory challenges related to produced water management.

Summary

While the variable composition and potential of contaminants in produced water poses significant challenges, progress has been made by the industry in developing advanced treatment technologies and disposal methods. From membrane filtration and thermal processes to beneficial reuse opportunities, operators now have a range of options for handling produced water responsibly.

This responsible management of produced water is more than just an obligation imposed by regulations but rather it is an integral part of oil and gas companies’ commitment to promoting environmental sustainability as well as creating a way for future generations while also addressing the global energy needs.

For any questions regarding produced water or any testing kits that we have to help you manage your testing needs smoothly, simply contact the world-class team at Atlas Scientific.

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