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Research and Application of Nanofiltration and Reverse Osmosis Technology in Oilfield Produced Water Treatment
Release date:2017/11/13 14:10:58

        Research and application of nanofiltration technology and reverse osmosis technology in oilfield produced water treatment and its application in industrial production and agricultural production, such as boiler water supply and agricultural irrigation. The disadvantage of reverse osmosis process is that the requirement and cost of treatment are relatively high. Therefore, how to choose the appropriate pretreatment scheme. And how to reduce the load of reverse osmosis unit to reduce the cost of treatment


        It is an inevitable trend for oilfield produced water to be treated and reused, which is conducive to promoting the sustainable development of oil and gas resources, and has great significance for water resources recycling and environmental protection. In the treatment of oilfield produced water, three filters (microfiltration, nanofiltration, ultrafiltration) and reverse osmosis membrane technology are widely used. Ultrafiltration is the best way to remove oil and turbidity in three filters, while nanofiltration is the best way to remove bivalent ions in produced water. In recent years, membrane treatment technology has gradually been widely used in oilfield produced water treatment.


  1. Traditional treatment technology of produced water


        The main treatment methods of produced water in domestic oilfields are biochemical method, physical method and chemical method. The purpose is to remove suspended matter, organic matter and oil in water. Physical methods can be divided into filtration, coarsening, evaporation, gravity separation and centrifugal separation. These methods focus on the removal of minerals and most of the solid suspended solids and oils in water. Chemical method includes three treatment methods, neutralization, coagulation and precipitation, and chemical conversion. Chemical method is mainly used to treat some colloids and soluble substances in wastewater, and the most important treatment is the oily substances in oily wastewater. Biological law mainly refers to aerobic biological method, anaerobic biological method and aerobic anaerobic biological method. Biological treatment of wastewater mostly uses microorganisms to degrade organic and toxic substances in wastewater in the process of metabolism, thus converting them into inorganic substances, so as to achieve the purpose of wastewater purification.


        In the actual situation of oilfield sewage treatment, these methods are generally not used alone, they are used in combination of two or three methods. When physical method is used to treat wastewater in Shengli oilfield sewage treatment station and water injection station in low permeability block, the treatment process is usually as follows: the first stage is "buffer + sedimentation separated oil + filtration" and the second stage is "buffer + fine filtration". In order to improve the effect of sewage treatment, chemical agents and physical methods are usually added to treat sewage in each sewage treatment station of oilfield.


        There are many kinds of bacteria in the produced water of oil field. These bacteria will corrode the pipeline of the produced water equipment, such as SRA, saprophytic bacteria and iron bacteria. These bacteria and their metabolites not only pollute the water quality, but also block the reservoir. Therefore, before reinjection, it should be sterilized. Generally speaking, the advanced oxidation method is used for sterilization. Advanced oxidation technology is very effective in eliminating SRB. At the same time, it can oxidize and degrade organic organisms in water, and disconnect the nutrient sources of bacteria. In order to achieve the purpose of sterilization, the sterilization technology of electrolytic brine can also be used. The saturated brine can be electrolyzed in the generator of sodium hypochlorite to produce sodium chlorate solution, which can be used to sterilize.


        The quality of produced water is also changing with the development of oil field. When surface technology is carried out, the use of flow modifier is inevitable, and the dosage of scale inhibitor, corrosion inhibitor, viscosity reducer and demulsifier is greatly increased. This is the main reason for the complexity of the components of produced water, which also causes the cost of wastewater treatment, the probability of secondary pollution and wastewater. It is more difficult to deal with. Therefore, according to the conventional treatment methods, the produced water can not meet the requirements of water quality standards. After a series of studies, membrane separation technology has a remarkable effect on the treatment of produced water.


        2. Research and Application of Microfiltration and Ultrafiltration Technology in Oilfield Produced Water Treatment


        2.1 microfiltration


        Membrane technology is characterized by high efficiency, relatively small unit area, low cost, less use of chemicals, and high automation of the unit. Therefore, membrane technology is more and more widely used in oilfield produced water treatment. Using static pressure difference as the driving force, and then separating the membrane through the "screening" effect of the screen-like filter medium membrane, is what we call microfiltration. Microporous filtration membrane is a homogeneous porous membrane, its pore size is very small, the diameter is generally 0.8-2 micron, the filtration particle size is 0.025-10 micron, so most of the suspended solids and oil droplets in the produced water can be completely filtered out. Ceramic membranes have been applied in many fields. They are easy to clean, resistant to pollution and corrosion, and have a long service life. Using ceramic membrane to treat produced water can make the quality of produced water meet the requirement of reinjection. The oil content of produced water is high before physical or chemical treatment, but not biochemical treatment. Therefore, the surface of microfiltration membrane will be polluted to varying degrees, resulting in the decrease of flux and oil retention, and the membrane can be cleaned to restore flux.


2.2 ultrafiltration


        Ultrafiltration membrane is mainly driven by pressure difference. Its pore size is very small, ranging from 0.001 to 0.02 um. It can separate particles with molecular weight greater than 2000 Dalton and particle size larger than 2 to 20 nm. Polymer and ceramic ultrafiltration membranes have been used in the study of oilfield produced water. from


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