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Application of sodium hypochlorite in recovery of oilfield wastewater

Sep10,24

With the development of China’s oil field exploitation industry, most oil fields have entered the late stage of oil production, and the output of oil field produced water is huge. The produced water contains more bacteria, which has an adverse effect on the pipeline and the environment. The principle of electrolytic salt sterilization technology commonly used in oilfield produced water is to use sodium hypochlorite generating device to produce sodium hypochlorite (NaClO) solution by electrolyzing salt water, and use sodium hypochlorite solution to achieve the purpose of sterilization. From the analysis of action principle, the technology belongs to oxidation sterilization technology. Sodium hypochlorite solution has strong oxidation, so that the bacteria in the produced water are irreversibly damaged, so as to play a role in sterilization. In the construction, electrolytic salt is added to sterilize and acidic agents are adjusted. At the same time, the addition of sodium hypochlorite bactericide can further eliminate the escape of trace odor substances. The whole set of sodium hypochlorite generator equipment is designed according to the actual needs of the site. It has the characteristics of good sterilization effect, automation, green economy, etc. It is an important development direction of oilfield produced water disinfection technology.

The source and water quality characteristics of oilfield wastewater:
Most of China’s oil fields are exploited by water injection (water injection fracturing), and about 2 to 3 tons of water are needed for every 1 ton of crude oil production. Therefore, often in crude oil exploitation, oil production wastewater also enters the gathering and transportation system with crude oil. In the late production period of special oil fields, the water content of crude oil can be as high as 90%. In addition, in the process of drilling and washing Wells, there are also wastewater generation, oilfield wastewater is a general term for the wastewater generated in the whole process of crude oil exploitation. Therefore, the water quality of oilfield wastewater is complex, containing oil, demulsifier, salt, phenol, sulfur and other environmental pollution substances. Its sources generally have the following aspects:
(1) After the water-bearing crude oil is mined out, the wastewater separated by the three-phase separator is the produced water;
(2) backwash the water injection well regularly to clean the washing water;
(3) Cleaning water generated by regular cleaning of oil storage tanks;
(4) Backwashing water generated after backwashing the pressure filter tank in the wastewater treatment station;
(5) Condensing wastewater in the station;
(6) Construction waste liquid, including drilling mud, fracturing fluid, acidizing residue, etc.
Produced water is the main source of oilfield wastewater.
Because of the complex composition of organic matter and inorganic matter in the water, it is difficult to treat oilfield wastewater. Although the water quality of each oilfield varies, it appears to have the following characteristics in general:
The high salinity accelerates the corrosion rate and also causes difficulties in the biochemical treatment of wastewater.
High oil content, far beyond the water quality standards required by various outlets,
Containing a large number of microorganisms, a large number of bacteria not only corrodes the pipeline but also causes serious blockage of the formation,
The produced water contains S042-, CO,2-, Ca2+, Mg2+, Ba2+ and other scale-forming ions. The content of suspended matter (polymer in polymer injection zone) is high, the particles are fine, and it is easy to cause formation blockage.

The harm of oilfield wastewater
A large amount of wastewater will be produced in the process of oilfield exploitation, especially in large-scale oilfield exploitation, and the water content of produced liquid is relatively higher. Oilfield wastewater is a complex liquid mixture, its main components are water, crude oil, soluble gas, solid suspended matter, electrolyte, bacteria and various oilfield chemical additives and other substances, direct discharge, will not only cause serious harm to the environment, pollute surface water and farmland, lead to the death of animals and plants and human potential diseases, cause serious harm to the lives of local people, but also, Acid gas or salt in oilfield wastewater will accelerate the corrosion of pipeline equipment. The solid suspended solids in oilfield wastewater will clog the formation. Industrial bacteria in oilfield wastewater will corrode pipelines, clog pipelines, and deteriorate water quality. Sodium hypochlorite generator only requires salt and water to generate 0.8%-12% concentration of sodium hypochlorite solution, effective sterilization, clean wastewater, and achieve sustainable use of water resources.

Oilfield wastewater treatment technology
Oilfield wastewater treatment mainly refers to the separation of crude oil, suspended impurities and harmful chemical ions in the water before the wastewater generated in the process of crude oil mining is injected back into the formation, so as to avoid pollution and damage to the geological structure and surface environment. Oilfield wastewater treatment technology includes physical method, chemical method, biological method and comprehensive physical and chemical method.
Physical method: A method for separating and removing water-insoluble suspended matter in oilfield wastewater by physical action. The equipment used in the physical treatment method is mostly simple, easy to operate, good separation effect, and very widely used, according to the different physical effects, the wastewater treatment mainly has gravity separation, centrifugal separation, pressure sedimentation, coarse granulation method and filtration method, etc., which are the use of different water treatment equipment to remove or reduce the harmful substances in the oilfield wastewater.
Chemical method:
1, chemical treatment method refers to the use of chemical reaction, by adding chemical agents to the wastewater or using electrochemical methods to remove harmful substances. Chemical agents are generally flocculating agents, flocculation method is mainly by adding flocculating agents to the wastewater, so that the suspended matter in the wastewater to form flocculation sinking, the process can not only remove the suspended matter and colloidal particles in the wastewater, reduce COD value, but also can remove bacteria and so on. The flocculants used in oilfield water treatment are mainly divided into inorganic, organic and biological flocculants. There are two main electrochemical methods, namely internal electrolysis method and electrochemical REDOX method. The internal electrolysis method (also known as the “iron-carbon method”) generally uses Fe as the anode of the galvanic cell, and the inert conductive substance in the oil as the cathode, resulting in a chemical reaction to produce Fe(OH) and Fe(OH)3 with a flocculent structure and strong adsorption force. Because dense oil will hinder the chemical reaction rate of the internal electrolysis method, this method is only suitable for the later stages of the oil treatment process. Electrochemical oxidation treatment mainly has two kinds of direct oxidation treatment and indirect oxidation treatment. The electrochemical oxidation method mainly acts on oxidizing substances, and the electrochemical reduction method is the opposite of the oxidation method, and the organic matter in the oil is directly electrolyzed, which can effectively reduce the sulfide in the oil.
2, chemical oxidation method, chemical oxidation is an effective method to transform pollutants in wastewater, which can transform the inorganic substances and organic matter in the dissolved state of wastewater into micro-toxic, non-toxic substances or into a form that is easy to separate from water. Chemical oxidation is the use of oxidizing agents (such as O2, 03, Cl2, CI02, NaCl0, H202, KMn04, KzFe04, bleaching powder, etc.) to oxidize and decompose pollutants such as oil and COD in wastewater to purify wastewater. NaClO sodium hypochlorite solution is highly oxidizing and is widely used in water treatment.
3, ozone – biological carbon technology
Ozone is used to remove odors from water and as a pretreatment before biological adsorption. It uses oxidation to remove dissolved organic matter and odor-producing substances in water, does not produce secondary pollution, and can also be used for in-depth treatment of microbial disinfection and sterilization. The removal of COD in oilfield wastewater improves the biodegradability for subsequent biological treatment, and greatly improves the biodegradability of organisms.
4, photochemical catalytic oxidation method
Photochemical oxidation method is an advanced oxidation technology that has developed rapidly in the past 20 years, using semiconductor materials (such as Ti02, Fe203WO, etc.) to degrade polluting substances such as oil and COD in wastewater by solar light or artificial light energy (such as ultraviolet lamps, fluorescent lamps, etc.) to achieve the purpose of purifying wastewater.
Physicochemical method: The use of physics and chemistry to purify the wastewater method. In the treatment of oilfield wastewater, the physicochemical methods mainly include gas floatation and adsorption. Air floatation is the use of buoyancy, through a lot of micro bubbles wrapped around the oil, the oil out of the water, and finally make the oil and water to achieve the purpose of separation. Adsorption method is the use of porous adsorbents to dissolve oil in wastewater by either physical adsorption (van der Waals force), chemical adsorption (chemical bond force) or exchange adsorption (electrostatic force) to achieve oil-water separation.
Biological method: Using the biochemical action of microorganisms, the complex organic matter is decomposed into simple substances, and the toxic substances are transformed into non-toxic substances, so that the wastewater can be purified. Biological treatment technology is currently the world’s most widely used wastewater treatment technology, the technology than physical or chemical methods of low cost, less investment, high efficiency, no secondary pollution, widely used by the chemical industry in various countries.

Application effect:
It can be known from the field information of an oilfield that the on-site preparation system of sodium hypochlorite has the characteristics of high bactericidal efficiency and stable bactericidal effect in the process of oilfield reinjection water treatment, and the cost is greatly reduced compared with the traditional chemical sterilization technology. Compared with commonly used organic fungicides, organic fungicides have ideal effects in a short period of time, but due to the improvement of bacterial resistance, the use of agents will continue to increase, and the treatment cost will also increase, and the on-site preparation of sodium hypochlorite will not produce resistance, and the dosage is uniform, which has quite good economic benefits. In addition, the sodium hypochlorite disinfection system also has the advantages of wide sterilization range, low toxicity, no leakage endangering human life and health safety, small toxic and harmful by-products, and little harm to the environment. Compared with ultraviolet disinfection, ammonia dioxide sterilization, ozone disinfection and other disinfection methods, the on-site preparation of sodium hypophyllate disinfection system has ideal disinfection effect and obtains better effluent water quality.

Sodium hypochlorite generator raw materials are easy to obtain, the process is simple, easy to install, can maintain the appropriate amount of residual hydrogen in the water body, to ensure that the subsequent water body will not occur in a short period of time, the equipment in the operation of a high degree of automation, safe and reliable, can work stable for a long time, does not produce pollution sources and dangerous points to the surrounding environment, with good social benefits. The one-time investment of equipment procurement cost is relatively high compared with other disinfection means, but saves a lot of personnel operating costs, from a long-term perspective, in line with the national energy conservation and emission reduction, green environmental protection development requirements, in the field of oilfield reinjection disinfection technology has great promotion value. BLUEWAV is a professional manufacturer of sodium hypochlorite generators, we have good experience in small plants and large plants, 12% sodium hypochlorite production up to 30 tons/day. With 20 years of global disinfection experience, the products are exported to more than 50 countries, including Italy, the United States, Saudi Arabia, Africa and other countries, and there are foreign companies in the local agent.
Bluewav Technology Co., Ltd. in China and the UAE
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