Трудности и узкие места при очистке сточных вод нефтяных и газовых месторождений

Characteristics of wastewater from oil and gas field development

Wastewater generated during the development of oil and gas fields has special treatment requirements due to its high salt characteristics. The high salt characteristics of these wastewaters mainly include the following aspects:

1. High mineralization: The mineralization of oil and gas field wastewater is usually very high, with a concentration range of 4000-60000 mg/L, and some as high as 150000 mg/L; this greatly increases the difficulty of wastewater treatment.

2. Contains multiple ions: The wastewater contains a large amount of Na, K, Cl, sulfate, calcium, magnesium and other ions. The presence of these ions makes the salt content of the wastewater far exceed the standard of farmland irrigation water. If it is discharged directly, it will cause serious pollution to the environment.

3. High concentration of organic matter: The organic matter content in oil and gas field wastewater is very high, and the COD (chemical oxygen demand) content may be as high as thousands or even tens of thousands. These organic matters still exist after treatment by general physical and chemical methods.

4. Microbial contamination: Wastewater may contain microorganisms such as iron bacteria, saprophytes, and sulfate-reducing bacteria. These microorganisms can cause pipeline corrosion and affect the operation of wastewater treatment facilities.

5. High hardness: The hardness of wastewater is high, with a concentration between 1000-20000mg/L, which may cause blockage of formations and pipelines.

6. High oil content: The oil content in wastewater is high, with a concentration between 200-1000mg/L, which not only increases the difficulty of oil-water separation, but also may block the formation during the reinjection process.

7. High suspended matter content: The concentration of suspended matter in wastewater is between 50-2000mg/L, and these suspended matter may also block the formation and affect the normal exploitation of oil and gas fields.

Difficulties in removing organic matter from high-salinity wastewater in oil and gas field development

There are many difficulties in removing organic matter from high-salinity wastewater generated in oil and gas field development. These difficulties are mainly due to the high salinity, complex composition and limitations of treatment technology of wastewater. The following is a detailed analysis of these difficulties:

1.The effect of high salinity on organic matter removal

Inhibition of microbial activity: The high salinity in high-salinity wastewater will significantly inhibit the growth and activity of microorganisms, thereby affecting the effect of biological treatment. Microorganisms are very sensitive to changes in environmental salinity. High salinity can cause dehydration or even death of microbial cells, making it impossible to effectively degrade organic matter in wastewater.

Increased treatment costs: In order to reduce the salinity in wastewater, it is usually necessary to dilute the wastewater, which will increase the amount of water used and the cost of treatment during the treatment process. At the same time, high salinity will also cause corrosion and damage to treatment equipment, further increasing the cost of maintenance and replacement of equipment.

2.Complexity of wastewater composition

Diverse types of organic matter: Oil and gas field wastewater contains a variety of organic matter, including hydrocarbons, phenols, alcohols, aldehydes, etc. The chemical properties and biodegradability of these organic matter are different, which increases the difficulty of removal.

Inorganic salts and other impurities: In addition to high salinity, wastewater also contains a large amount of inorganic salts, heavy metal ions, suspended matter and other impurities. These impurities will form complex compounds with organic matter, further reducing the degradability of organic matter.

3.Limitations of treatment technology

Limitations of biological treatment: Although biological treatment has the advantages of low cost and good effect in wastewater treatment, as mentioned above, high salinity will significantly inhibit the activity of microorganisms, thus limiting its application. In addition, biological treatment systems have poor adaptability to water quality fluctuations and environmental changes, and are easily impacted, resulting in reduced treatment effects.

Challenges of physical and chemical treatment: Although physical and chemical methods such as evaporation, electrolysis, and ion exchange can remove salt and organic matter in wastewater, they usually face problems such as high cost, high energy consumption, and easy secondary pollution. Especially for the removal of organic matter in high-salinity wastewater, these methods often fail to achieve the desired effect.

4.Solutions and future directions

Pretreatment and dilution: Remove impurities such as suspended matter and heavy metal ions in wastewater through pretreatment, and appropriately dilute the wastewater to reduce salinity, creating favorable conditions for subsequent treatment.

Optimize biological treatment process: Screen and domesticate microbial strains that can grow in high-salinity environments to improve the adaptability and treatment efficiency of biological treatment methods. At the same time, a combination of multiple biological treatment processes can be considered, such as aerobic-anaerobic combined treatment.

Innovative physical and chemical treatment technology: Develop new high-efficiency, low-energy consumption, and low-pollution physical and chemical treatment technologies, such as advanced oxidation technology and membrane separation technology, to improve the efficiency of organic matter removal and reduce treatment costs.

Resource utilization: Explore ways to utilize salts and organic matter in oil and gas field wastewater, such as recovering salt resources through evaporation and crystallization, and converting organic matter into valuable chemicals or energy substances through biological or chemical transformation.

Solutions for removing organic matter from high-salinity wastewater in oil and gas field development

The solution for removing organic matter from high-salinity wastewater generated by oil and gas field development can be considered comprehensively from multiple aspects, including pretreatment, biological treatment, physical and chemical treatment, and resource utilization strategies. The following are some specific solutions:

1. Pretreatment

Removal of suspended matter and heavy metals: Remove suspended matter, large particle impurities, and heavy metal ions in wastewater through physical methods (such as precipitation and filtration) to reduce interference with subsequent treatment processes.

Adjusting pH value: Adjusting the pH value of wastewater to a range suitable for subsequent treatment processes will help improve the treatment effect.

Dilution: When necessary, high-salinity wastewater can be diluted by adding fresh water or other low-salinity wastewater to reduce its salinity, but care should be taken to control the dilution ratio to avoid increasing excessive treatment costs.

2. Biological treatment

Screening and domestication of salt-tolerant microorganisms: Screening and domestication of microbial strains that can grow in high-salinity environments. These strains have strong degradation capabilities for organic matter and can effectively remove organic matter from wastewater under high-salinity conditions.

Bioreactor design: Design bioreactors suitable for high-salinity wastewater treatment, such as using anaerobic-aerobic combined treatment processes to improve biodegradation efficiency.

Adding bioenhancers: Adding bioenhancers, such as enzyme preparations, microbial agents, etc., to the biological treatment system to accelerate the degradation process of organic matter.

3. Physical and chemical treatment

Advanced oxidation technology: using ozone, Fenton reagent, ultraviolet light and other advanced oxidation technologies to produce strong oxidative free radicals, oxidize and decompose the difficult-to-degrade organic matter in the wastewater into small molecules, and even mineralize into carbon dioxide and water.

Membrane separation technology: using ultrafiltration, nanofiltration, reverse osmosis and other membrane separation technologies, the organic matter and salt in the wastewater are separated through the selective permeability of the membrane. These technologies are very effective in removing organic matter and salt in high-salt wastewater, but the cost is high and suitable for occasions with high requirements for effluent water quality.

Adsorption and ion exchange: using activated carbon, resin and other adsorbents or ion exchange resins to remove organic matter and specific ions in wastewater. This method is suitable for wastewater with small treatment volume or high organic concentration.

4. Resource utilization

Evaporation and crystallization to recover salts: the salt in the wastewater is concentrated and recovered through the evaporation and crystallization process to obtain industrial salt or use it in other fields. This can not only reduce the salt content in the wastewater, but also achieve resource recycling.

Organic matter conversion and utilization: Explore the conversion of organic matter in wastewater into valuable chemicals or energy substances (such as biodiesel, hydrogen, etc.) through biological or chemical conversion technology. This method can not only remove organic matter in wastewater, but also realize the resource utilization of waste.

5. Comprehensive treatment

Multi-process combination: According to the specific characteristics and treatment requirements of wastewater, the above-mentioned multiple treatment processes are combined and optimized to form a comprehensive treatment plan. For example, suspended matter and heavy metal ions can be removed by pretreatment, and then most of the organic matter can be removed by biological treatment, and finally the water quality can be further purified by physical and chemical treatment.

6. Intelligent management: Introduce an intelligent management system to monitor and control the wastewater treatment process in real time to ensure stable and reliable treatment effects and reduce operating costs.

What are the advantages and disadvantages of high-salt wastewater treatment technology?

The advantages and disadvantages of high-salt wastewater treatment technology vary depending on the specific technical methods. The following is an overview of the advantages and disadvantages of some common high-salt wastewater treatment technologies:

1.Evaporation and crystallization method

Advantages:

High desalination rate: Through the evaporation process, the salt in the wastewater can be highly concentrated and crystallized to achieve effective removal of salt. The concentration multiple is “theoretically” unlimited.

Good treatment effect: It can significantly reduce the salt content in the wastewater, and the water quality after treatment is relatively stable.

Resource recovery: Crystallized salt can be recycled as a by-product and has certain economic value.

Disadvantages:

High energy consumption: The evaporation process requires a lot of heat energy, resulting in high energy consumption.

Complicated equipment and high investment: Evaporation and crystallization equipment is relatively complex and requires professional operation and maintenance.

High operating cost: Due to factors such as energy consumption and equipment maintenance, the operating cost is relatively high.

2.Membrane treatment method (such as reverse osmosis, nanofiltration)

Advantages:

Efficient salt removal: The membrane treatment method has a high desalination rate and can effectively remove salt from wastewater.

High water quality: The treated water is clear and suitable for reuse or further treatment.

Small footprint: Membrane treatment equipment is relatively compact and occupies a small area.

Disadvantages:

High energy consumption: Especially for wastewater with high salt concentration, a high-pressure pump is required to provide sufficient pressure, which consumes a lot of energy.

Membrane pollution: After long-term use, the membrane is easily contaminated and needs to be cleaned or replaced regularly, which increases maintenance costs.

High equipment cost: The initial investment cost of membrane treatment equipment is high.

3.Ion exchange method

Advantages:

Effective salt removal: Ion exchange resin can selectively remove salt and other ions in wastewater.

Mature process: Ion exchange technology is relatively mature and easy to operate.

Disadvantages:

High resin regeneration cost: For wastewater with high salt concentration, frequent resin regeneration or replacement is required, which increases the treatment cost.

Waste liquid treatment: The waste liquid generated during the resin regeneration process needs to be properly handled to avoid secondary pollution.

4.Biological treatment method

Advantages:

Environmentally friendly: Biological treatment uses the metabolism of microorganisms to degrade organic matter and salt in wastewater without the addition of chemical agents.

Low operating cost: Compared with other physical and chemical methods, the operating cost of biological treatment is lower.

Disadvantages:

The treatment effect is greatly affected by water quality: Biological treatment has high requirements for water quality conditions and is greatly affected by factors such as the type, concentration and salinity of organic matter in the wastewater.

Long treatment cycle: Biological treatment usually requires a long treatment cycle to achieve the ideal treatment effect, and cannot meet the requirements of rapid discharge, rapid treatment and timely digestion of “oil and gas field wastewater”.

What environmental protection laws and regulations need to be followed when treating high-salt wastewater

When treating high-salt wastewater, the environmental protection laws and regulations that need to be followed mainly include:

1. “Environmental Protection Law of the People’s Republic of China”: As the basic environmental protection law of the country, it stipulates the environmental protection responsibilities of enterprises in the process of resource development, requires effective measures to reduce environmental pollution and ecological damage, strengthen environmental risk prevention, and promote technological progress.

2. “Water Pollution Prevention and Control Law of the People’s Republic of China”: stipulates the protection requirements for the water environment, including wastewater discharge standards and pollution prevention and control measures, to prevent water pollution, protect and improve environmental quality.

3. “Comprehensive Wastewater Discharge Standard” (GB8978-1996): stipulates the national standards for wastewater discharge, including the concentration limit of various pollutants in wastewater, ensuring that wastewater can only be discharged after being treated to meet the standards.

4. “Technical Policy for Pollution Prevention and Control in Petroleum and Natural Gas Extraction Industry”: issued by the Ministry of Ecology and Environment, it provides specific technical policy guidance, including clean production, ecological protection, pollution control, new technologies encouraged for research and development, as well as operation management and risk prevention.

5. “Technical Specifications for Oil Production Wastewater Treatment Engineering” (HJ 2041-2014): provides technical requirements for the design, construction, acceptance and operation management of oil production wastewater treatment projects, and is a guiding document.

6. “Technical Guidelines for High-Salt Organic Wastewater Treatment Engineering” (Draft for Comments): Although it is a draft for comments, it provides technical guidelines for the treatment of high-salt organic wastewater, including technical requirements for design, construction, operation and maintenance.

Compliance with these regulations is an important guarantee to ensure that high-salt wastewater treatment meets environmental protection requirements and prevents environmental pollution and ecological damage. At the same time, during the wastewater treatment process, enterprises should also pay attention to the specific implementation rules and guidelines issued by local environmental protection departments to ensure that the wastewater treatment process and results comply with the requirements of laws and regulations.