Significance of oilfield wastewater treatment

Oilfield wastewater includes mainly oilfield produced water, drilling wastewater and other types of oily wastewater. Oil wastewater quality is complexed, often containing petroleum demulsifiers, salt, phenol, sulfur and other environmental pollutants, and its oil content or the oil presence in the water differ from case to case, occurs in most cases different from the regular mixed phase with water, in order to better deal with this situation, in practice often use combined application of various methods and targeted for treatment, so that the water quality can meet emission standards.

Oilfield wastewater treatment aimed at the removal of oil, additives, suspended solids and other impede water, and could easily lead to corrosion and water injection system fouling harmful ingredients. Under normal circumstances oilfield wastewater treatment technology and methods used include gravity separation, flotation, filtration, coarse-grained and biological method. Oilfield chemicals are widely used in the petroleum industry in various fields of chemistry and chemical engineering products or natural chemicals. In the process of oilfield wastewater treatment chemicals commonly used are fungicides, corrosion inhibitors, scale inhibitors, flocculants and sulfur removal agent. Of course, the water component for each field is different significantly; water after treatment and requirements reuse of water quality are also different, so the treatment process requires a choice. In summary, here present developed novel agents and new technology and equipment, as well as the application of new technologies for the development of new trends in the field of sewage treatment.

Application of oilfield chemicals

Oilfield wastewater treatment based on oil production can have a variety of different uses ways. The main hazard is the corrosion of oilfield wastewater pipelines and equipment fouling and contamination of the oil carried in order to solve these problems, it is often used with fungicides, scale inhibitors, corrosion inhibitors, flocculants, sulfur remover and the alike.

1, Sterilization and Corrosion inhibition

Oilfield wastewater contains large amounts of bacteria, bacterial activity and metabolites of oil production is a big problem. At the same time after the period in oilfield development, the role of physical chemistry will produce a lot of H2S, C02, Cl, SO42-. And other corrosive substances, and these substances are dissolved in the pore water to form acidic fluid, causing corrosion of downhole string.

Fungicides are generally divided into two categories: oxidized and non-oxidized, mainly by the differences in the use of the function and its composition. Oxidizing biocides to maintain the efficacy of a short time, the usage with large quantity, easily causing environmental pollution, it is rarely adopted in the field, rather than oxidizing biocides without these negative factors, has been widely used in the oil field. Non-oxidizing biocides based on the difference of its bactericidal effect and mechanism of radical species, generally divided into: quaternary ammonium salts, quaternary phosphorus, organic aldehydes, cyanide compounds, heterocyclic compounds, compound fungicides, multifunctional fungicides.

Versatility of metal corrosion inhibitor can control effectively control, according to their chemical composition differences can generally be divided into inorganic and organic corrosion inhibitor. Organic corrosion inhibitors include imidazoline inhibitor, ammonium and quaternary ammonium salts, corrosion inhibitors, multi-functional organic corrosion inhibitors, low toxicity and efficient organic corrosion inhibitor, oligomeric or condensation polymerization inhibitor, heterocyclic inhibitor, etc., with respect to the type of inorganic corrosion inhibitors less organic corrosion inhibitors, and it can only work effectively at high concentrations. Chromate corrosion of ferrous metals with a prominent role in the effect had been widely adopted, but with the enhancement of environmental protection requirements make its usage subject to certain restrictions. Molybdate, tungstate and rare earth compounds are currently developing applications of ring embankment friendly inorganic corrosion inhibitors.

2, Flocculation, Scale Inhibition and Sulfur Removal

In oilfield wastewater some natural impurities and chemical additives, such as soluble salts, solids, heavy metals, suspended emulsified oil, hydrogen sulfide, etc., as well as injected acids, lubricants, biocides, oxygen scavengers, antifouling agents, all of them can cause blockage, pipeline corrosion, and their emission also cause pollution. Currently, chemical flocculation process is commonly used in oil companies, as a pretreatment technique in combination with gas float. Flocculant is to prevent these factors arising from a class of oilfield chemicals, flocculants used are mainly divided into three species: inorganic flocculants, organic flocculants and composite flocculant. Organic polymer flocculant has properties of less dosage, fast processing speed, high efficiency and less sludge output, etc., along with research and development in recent years, its research and application plays an important role in the oilfield wastewater treatment.

Oilfield wastewater fouling is an inevitable problem in the production process, its effect increases along with the increase of output water. Water often contains dirt addition CaCO3, CaSO4, SrSO4, BaS04, also MgC03, MgS04, Mg (OH)2, Ca3 (P04)2, SiO2 and alike. Fouling problems posed a serious impact on oil production, thus enhancing the study of scale may well avoid or reduce the loss of the oil industry, and bring some economic benefits. Recently, a chemical inhibitor to inhibit scale formation is the most common scale inhibition method, along with the development and progress of related technologies, inhibitor development frontier will transit from inorganic substances to organic polymers, from phosphorus type to phosphate-free and environment-friendly type.

Presence of sulfur in Oilfield wastewater is mainly as mode of S, S2-, SO42-, S, SO42-. It Is reduced to S2- by the role of sulfate-reducing bacteria, while S2- has a very strong corrosion to steel, it can lead to wall perforation, interferes with the normal production, furthermore its corrosion degraded product is black suspension FeS, insoluble in water, leading to increase of suspension substance; FeS is an emulsified oil stabilizers, further increases the difficulty of separation of oil. At present, chemical agents is widely used,  sulfur removal agent is commonly precipitated by physical or chemical oxidation reaction to achieve the effect of sulfur removal, which can be divided into two types: oxidizer type and precipitation type.

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