Salty High TDS Water, Wastewater Treatment Plant in Oilfields and Gas fields

Introduction

In extraction activities for oil and gas, water serves as a tool of trade. Its uses are spread over several phases: drilling, hydraulic fracturing, and enhanced oil recovery. However, this is no ordinary water; often, it is characterized by high levels of total dissolved solids, causing it to be saline that makes it difficult to govern. The high TDS levels in the water present grave challenges both to the environment and to the operational efficiency of the extraction process of oil and gas. If left untreated, the water can cause equipment scaling and corrosion, increase operational costs, and create significant environmental hazards if improperly disposed of.

Advanced water treatment technologies are necessary to minimize such risks and achieve a certain level of sustainability. They aim to reduce the TDS levels in water to enable its reuse or safe disposal. The treatment process of high TDS water is intricate and will require a combination of methods including Ultrafiltration (UF), Reverse Osmosis (RO), and Multi-Effect Evaporators (MEE). Each of these technologies is part of the solution for the peculiar problems associated with water management in oil and gas fields.

We discusses the details of how to treat high TDS waters while exploring oil and gas. Treatment of these types of waters is meticulous in discussion, involving the description of the kinds of waters encountered, the analysis of their chemical composition, and the peculiar problems they pose. This paper further discusses the advanced treatment technologies offered and the reality of implementation with environmental and economic costs that are inherent to it.

Understanding Water Characteristics in Oilfields and Gas Fields

Types of Water Produced

Water is the unavoidable byproduct that results from the processes involved in the extraction of oil and gas. The changes at the stage and methods used during extraction result in different water types with comparatively different characteristics and problems. Produced water, flowback water, and injected water are the three types of water generally associated with oil and gas fields.

1. Produced Water
   Produced water is the water that emerges simultaneously with oil and gas from a well during production. Undoubtedly, this variety of water is the biggest source of water within oilfields and can constitute up to 90% of the total liquid that is extracted from a well. This water is usually a mixture of water naturally existing in the geological formation, known as formation water, with various types of water that are injected into the formation to enhance recovery of oil. Produced water is typically extremely high in TDS, often exceeding 10,000 to over 300,000 mg/L. Moreover, it contains a wide variety of organic and inorganic compounds, including hydrocarbons, heavy metals, and naturally occurring radioactive materials, making it one of the most challenging categories of water to manage.
2. Flowback Water
   Flowback water refers to fluid resurfacing after hydraulic fracturing, popularly known as fracking. It consists of a mixture between the well-injected water, otherwise frack fluid, and formation water that becomes part of the combination while fracturing. In most cases, high TDS concentration characterizes flowback water; however, compared to produced water, the concentration is usually lower. While this, according to various reports, ranges in TDS levels from a few thousand to more than 100,000 mg/L depending on the geological formation and the fracking fluid composition, it also includes a suite of chemical additives used in the fracturing process besides the dissolved minerals and organic compounds that make its treatment equally complex.
3. Injected Water
   Injected water is an important element in all EOR methodologies, where water is injected in a reservoir for pressure maintenance and for oil extraction. This water is often from surface water, groundwater, or treated produced water. Although the TDS concentration levels in the injected water could be extremely different, depending on its source, the main serious problem remains the compatibility of this water with the reservoir rock/fluids. Injected water with too high or too low Total Dissolved Solids will result in scaling, souring of the reservoir, and other operations-related problems.

Composition of High TDS Water

The production waters from oil and gas wells possess high TDS levels due to a large proportion of dissolved salts and minerals. The constitution of such produced waters varies to a great degree and is dependent upon the geological formation, type of hydrocarbon extracted, and extraction methods employed. These are the most common major constituents that contribute to the high total dissolved solid basis in these waters:

1. Sodium Chloride (NaCl)
   Sodium chloride, or common table salt, is usually the most dominant salt in high TDS produced water coming from oilfields and gas fields. The concentrations may vary extremely from tens of thousands to more than 200,000 mg/L. High concentrations of sodium chloride can make the water very saline but at the same time significantly contribute to corrosion and scaling problems inside pipelines and process equipment.
2. Calcium and Magnesium Salts
   Present in substantial quantities in high TDS water are calcium and magnesium, generally as chlorides and sulfates. These ions are directly responsible for water hardness and result in pipe and apparatus scaling. The particular difficulty arises with CaSO₄ and MgSO₄, since the latter compounds are less soluble and more prone to precipitating as scale.
3. Bicarbonates and Carbonates
   The concentration of bicarbonates differs from that of carbonates. Whereas these ions are generally less efficient at inducing scaling compared to calcium and magnesium, they can sometimes enable the creation of carbonate scales under certain conditions, particularly if the water is supersaturated with respect to calcium carbonate.
4. Heavy Metals and Trace Elements
   Produced water from some oilfields and gas fields can have high TDS values with contents of high levels of heavy metals, including Fe, Mn, Pb, and As. These metals could come from the geologic formation itself or infrastructure corrosion. The presence of these contaminants makes treatment processes more difficult and is an environmental and health concern if the water is disposed of improperly.
5. Organic Compounds and Hydrocarbons
   Apart from inorganic salts, high TDS water coming from oilfields and gas fields is normally rich in a myriad of different types of organic compounds. They include dissolved hydrocarbons, volatile organic compounds, and naturally occurring organic acids. These types of compounds give additional complexity to the water because of their potential to interfere with the treatment process or cause environmental problems.
6. Naturally Occurring Radioactive Materials (NORM)
   In some cases, water high in total dissolved solids (TDS) may also contain low levels of naturally occurring radioactive materials (NORM), such as radium-226 and radium-228. These are typically present in formation water and may accumulate in scales and sludges, making long-term disposal difficult.

Water Treatment Technologies

Handling high Total Dissolved Solids (TDS) water in oil and gas fields is a multifaceted task that requires modern technologies to be applied to make water either suitable for reuse or easily disposed of. The presence of high levels of salts, minerals, organic compounds, and other pollutants makes common water treatment methods unsuitable and complex, innovative technologies must be applied. The chapter will consider the main technologies involved in the treatment of high TDS from water, in particular highlighting ultrafiltration, reverse osmosis, and multi-effect evaporators. All of these methods are cardinal toward reducing the levels of TDS, removing contaminants, and maintaining standards into the treated water for either re-use or discharge.

The treatment of water in oil and gas exploration is normally a complex process, involving mainly physical, chemical, and thermal procedures for treatment. Proper treatment technology would depend on several factors, which are the composition of the water, quality required for the treated water, and operational requirements at an oilfield or gas field. The primary objectives of such treatments will be to minimize TDS levels, eliminate hazardous contaminants, and recover as much of the water as possible for re-use. An overview of key technologies used in treating high TDS water is presented below.

1. Ultrafiltration (UF)
   Ultrafiltration is a quite frequently used, membrane-based technology as a pre-treatment step in most water treatment processes. The pore size of ultrafiltration membranes ranges between 0.01 and 0.1 microns, making them quite efficient in removing suspended solids, bacteria, viruses, and high-molecular-weight organic compounds from the aqueous medium. Although ultrafiltration is generally not used for removing dissolved salts—making up the bulk of TDS—it does play a vital role in protecting downstream processes like reverse osmosis from fouling and damage.In view of this fact, ultrafiltration becomes a very important step during the pretreatment stage in a water treatment process, particularly for waters with high TDS. The chief role that UF plays is the removal of suspended solids, colloidal particles, and larger organic molecules from the water, which helps avoid fouling and clogging in further steps of treatments such as RO.

   Mechanism of Ultrafiltration

   Ultrafiltration membranes follow the principle of size exclusion, wherein particles larger than the membrane pore size are retained on the surface while smaller molecules like water pass through easily. The pore diameter of ultrafiltration membranes ranges normally between 0.01 and 0.1 microns; hence, they are very effective in removing bacteria, viruses, and colloidal substances. The process is driven by pressure, where water is pushed via the membrane at pressures ranging from 1 to 10 bar.

   

2. Reverse Osmosis (RO)
   One of the most used technologies to reduce TDS in water is Reverse Osmosis. RO works by forcing the water through a semipermeable membrane that allows the water molecules to pass but rejects most dissolved salts, minerals, and other contaminants. On completion of the process, a permeate stream with considerably reduced TDS and concentrated brine streams containing the rejected salts and contaminants are formed.Reverse osmosis becomes a very critical technology to reduce TDS levels in water, more so in an environment where the water is extremely saline. RO has maximum efficiency in the desalination process and, therefore, happens to turn out to be the most important tool in the treatment of high TDS water in oilfields and gas fields.

   Mechanism of Reverse Osmosis

   RO functions based on the principle of osmosis, in which water goes by nature from an area of low solute concentration to an area of high solute concentration across a semi-permeable membrane. In RO, this natural process is reversed by pressurizing the saline water and forcing it through the membrane. Water molecules can pass through a semi-permeable membrane with ease; however, most of the dissolved salts, ions, and other contaminants are rejected by it. The resulting two streams will include a low-TDS permeate stream and a high-TDS concentrate or brine stream.

3. Multi-Effect Evaporators (MEE)
   Multi-Effect Evaporators are units for thermal desalination that involve several steps of evaporating the water and condensing it to fresh water while leaving concentrated brine behind. The MEE technique is particularly good at treating very high TDS levels in water, where other technologies like RO might not be feasible or cost-effective.Multi-Effect Evaporators are desalination units particularly suited to treating very high TDS level waters, where other technologies like RO might not be practical or cost-effective. MEE is an assured technique for high water recovery, especially in hostile operating environments like oilfields and gas fields.

Mechanism of Multi-Effect Evaporators

MEE consists of the basic working principle where trains of successive stages, or effects, are utilized for progressively evaporating water and condensing the vapor for drinking water. The boiling point of water in each effect is lowered, and the steam formed in one effect serves to be used for heating the next effect, thereby further raising energy efficiency. Usually, the process involves several evaporations and condensations from which not only fresh water but also concentrated remaining brine is recovered.

Integrating Technologies for Optimal Treatment

In practical applications, the treatment of high TDS waters in oilfields and gasfields usually integrates several technologies to meet the desired water quality. For instance, the typical treatment train will initiate with ultrafiltration to remove suspended solids, followed by reverse osmosis to reduce TDS levels and then multi-effect evaporators to further concentrate the brine and recover additional water. This multi-phase, holistic approach ensures that each of the technologies incorporated is used to maximum efficacy, enabling the company to ably respond to all challenges that the water composition and field operations dictate.

1. Pre-Treatment with UFIn using UF as a pretreatment step, RO membrane fouling can be avoided downstream, and their operating life can be extended because UF will remove larger particles and colloidal matter to ensure that water going through the RO system is as clean as possible.
2. Primary Desalination with RORO is the primary desalination step, and thus it reduces TDS levels in water to a large extent. Normally, the permeate from the RO system can be reused for most operational processes, while the concentrate is further sent for treatment or disposal.
3. Final Concentration with MEEFurther concentration of the RO concentrate can be made with MEE to recover more water and further concentrate the brine. In particular, this step is very valuable in water-scarce regions where maximal water recovery is a priority.

Case Studies and Practical Applications

Advanced water treatment technologies are required for the management of high TDS water in oil- and gas-fields. In this context, such technologies would have to attain operational efficiency, while at the same time maintaining environmental sustainability. In this section, therefore, applications of advanced technologies are demonstrated in practical cases to show how successfully companies like Waterman Engineers Australia have used them in difficult tasks.

High TDS Water Treatment in a Middle Eastern Oilfield

It is in this environment, within a large oilfield in the Middle East, that challenging environmental conditions and high TDS produced water presented operators with large operational problems due to scaling and corrosion. The produced water was above 200,000 mg/L TDS value, mainly sodium chloride, calcium, and magnesium salts. The high salinity presented severe risks to the infrastructure of the field from pipelines through to storage tanks.

High TDS Water Treatment in an Offshore Oil Platform

However, this remote platform, located offshore Southeast Asia, was encountering produced water with >150,000 mg/L TDS, with additional high levels of organic contaminants and heavy metals. In such a scenario, the treatment of water for overboard discharge would become even more complicated due to the remote nature of this platform.
In this regard, the system put in place by Waterman Engineers Australia has resulted in an autonomous and sustainable water treatment solution that will enable the facility to operate well with a minimal ecological footprint.

Solution by Waterman Engineers Australia

Waterman Engineers Australia was approached to design and deliver an integrated water treatment system with the capacity to meet the extreme salinity and challenging operational conditions. This solution would involve a multi-layered treatment process:

• Ultrafiltration (UF) was the first stage to remove the suspended solids and colloids in order to protect the downstream processes from fouling.
• RO was thus used to bring down the TDS considerably and provide a permeate stream suitable for re-use into the field’s operations.
• MEEs were installed for the RO concentrate treatment step, further decreasing the volume of brine and recovering more water for re-use.

The system developed by Waterman Engineers Australia led to a significant reduction in scaling and corrosion problems, extended the life expectancy of the field’s infrastructure, and facilitated the re-injection of treated water that results in reduced reliance on freshwater resources.

Conclusion

High TDS water management is one of the vital functions that operations in today’s oil and gas fields execute. The drivers for this are infrastructure protection, minimization of environmental impact, and pursuit of sustainable uses of water are significant. State-of-the-art technologies like UF, RO, and MEE come to the forefront as important enablers for handling complex and difficult water compositions within operational settings.

In sum, by implementing these technologies, businesses can reduce the level of TDS, purify water from hazardous contaminants, and obtain processed water for reuse to an extent that minimizes the intake of fresh water, therefore reducing the environmental burden associated with oil and gas exploration. The case studies presented provide insight into the applications of these technologies in different settings, outlining the need for customized solutions to meet specific operational and ecological requirements.

Waterman Engineers Australia has developed such expertise in high TDS water treatment for oil and gas fields, providing leading-edge solutions to meet the special needs of individual projects. Its leadership in the design and delivery of advanced water treatment systems empowers operators in improving operational efficiency, extending infrastructure life, and meeting sustainability goals.

Effective water management in oil and gas operations will remain needed as long as demands for energy increase. In this respect, technological innovation and specialized expertise by firms like Waterman Engineers Australia shall reduce the challenges and thus make the industry thrive while being conservative of the planet’s vital resources.

FAQs

1. What is high TDS water, and why is it a concern in oilfields and gas fields?
   High TDS water is concentrated with dissolved salts and minerals. It poses several problems in oilfields and gas fields as it causes scaling, corrosion, and environmental pollution. High TDS levels also make the water unsuitable for reuse without proper treatment, leading to operational challenges and increased expenses.
2. What technologies are commonly used to treat high TDS water in oilfields and gas fields?
   Common technologies for treating high TDS water include ultrafiltration, reverse osmosis, and multi-effect evaporators. These technologies work together to remove suspended solids, reduce TDS levels, and concentrate brine, making the final water suitable for reuse or safe disposal.
3. How does Ultrafiltration (UF) help in the water treatment process?
   Ultrafiltration is a membrane technology that effectively removes suspended particulates, bacteria, and large organic compounds from water. It is used at the initial stages of treatment to protect other processes, like reverse osmosis, from fouling and damage, thereby improving the overall efficiency and lifespan of the treatment system.
4. Why is Reverse Osmosis (RO) a preferred method for desalinating water in oilfields?
   Reverse osmosis is preferred because it reduces TDS levels by up to 99%, effectively removing dissolved salts and other impurities from water. This treatment makes the water fit for recycling into various uses, reducing reliance on natural fresh water resources and mitigating environmental impacts.
5. What are Multi-Effect Evaporators (MEE), and when are they used in water treatment?
   Multi-effect evaporators are thermal desalination units used for treating very high TDS levels in water. They evaporate water into fresh water and condense it, leaving concentrated brine behind. MEE is particularly useful in environments where other desalination technologies, like RO, might not be feasible or cost-effective.
6. How does Waterman Engineers Australia approach high TDS water treatment in oilfields and gas fields?
   Waterman Engineers Australia provides integrated solutions for treating high TDS waters using ultrafiltration, reverse osmosis, and multiple-effect evaporation. They offer customer-specific solutions tailored to the unique requirements of each project, ensuring efficient water treatment with lower operational costs and reduced environmental impact.
7. How does Waterman Engineers Australia ensure the sustainability of water treatment processes?
   Waterman Engineers Australia focuses on sustainability by developing water treatment systems that maximize water recovery, minimize solid waste generation, and reduce environmental impact. Their approach emphasizes energy efficiency, reduced chemical usage, and safe reclamation or disposal of treated water.
8. What is the role of pre-treatment in high TDS water treatment?
   During high TDS water treatment, ultrafiltration is used as a pre-treatment step to remove suspended solids, colloidal particles, and larger organic molecules. This critical step protects downstream processes, like reverse osmosis, from fouling and enhances the efficiency and longevity of the treatment system.
9. What makes Waterman Engineers Australia a leader in high TDS water treatment?
   Waterman Engineers Australia is a leader in high TDS water treatment due to their expertise in designing and delivering state-of-the-art water treatment systems for oilfields and gas fields. They provide tailored solutions for each project, ensuring efficient, cost-effective, and environmentally sustainable water management. Their extensive experience in varied and challenging environments further underscores their leadership in the field.