Study on treatment technology of oily sludge in oil and gas field

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Abstract: the physical and chemical properties of oily sludge are complex, and its treatment is a big problem that puzzles the petroleum industry.
Based on this, the treatment standards of oily sludge are introduced, several treatment technologies of oily sludge in oil and gas fields are analyzed, and the trend of oily sludge treatment prospects.

It is difficult to treat the oily sludge in oil and gas fields. Most of the oil fields have not realized the harmless and resource-based treatment. Generally, the way of stacking and drying after dehydration will not only occupy a lot of lands, but also pollute the air, water, and soil. Therefore, enterprises also need to pay a large number of sewage charges.
It is necessary to further study the treatment technology of oily sludge in oil and gas fields.

1. Treatment standard of oily sludge

The treatment standard of oily sludge in oil and gas fields usually depends on the use of sludge after treatment. Generally speaking, the final disposal of such sludge at home and abroad is road construction and landfill. In order to avoid adverse impact on the soil in the landfill areas, countries have put forward strict requirements for heavy metal content and oil content after the treatment of oily sludge.

For example, the United States and France require oil content ≤ 2% (mass fraction of oil) for oily sludge in landfill disposal and ≤ 5% (mass fraction of oil) for oily sludge in road construction disposal.

2. Treatment technology of oily sludge in oil and gas fields

2.1 Decrement treatment
Reduction treatment is to separate the particles from sludge by physical and chemical methods, so as to realize the reduction of pollutants. This method has the characteristics of low cost and easy operation.

2.1.1 mechanical dehydration
Mechanical dehydration is a kind of pretreatment of oily sludge, such as conditioning, sorting, etc., and then high-speed centrifugation to separate oil, water, and mud, and then according to the treatment effect, auxiliary treatment is carried out by using solidification technology, biotechnology, etc., so as to realize the harmless treatment of oily sludge.

1) Flocculant was used to adjust the particle structure of oily sludge and enhance its dehydration.
2) Vacuum filter dehydrator, high-speed centrifuge, and other equipment are used for dehydration.
Among them, flocculants are difficult to degrade, and poor treatment will lead to secondary pollution. Therefore, the selection of high-efficiency, organic, and polymer flocculants with wide application range, innocuity, and innocuity is a key issue to be considered, and the emerging polymer flocculants secreted by microorganisms is a better choice.

2.1.2 incineration
Incineration is the main way to treat oily sludge in a sewage treatment plant.
After dehydrating the oily sludge, it is sent into the concentration tank, heated to 60 ℃, then added with flocculant, stirred and gravity settled, and then cut water in layers.
After the above treatment, the oily sludge can be dehydrated and dried again, made into mud cake, burned in the incinerator, and finally treated with ash.
The effect of incineration treatment is very obvious, it can remove a variety of harmful substances, but it will also release some harmful gases in the incineration process, causing two times of air pollution.
Finally, the incineration treatment requires high equipment, which is also a condition that many oil and gas fields do not have.

2.2 curing treatment

2.2.1 curing treatment
Solidification refers to the innocuous treatment that means that oil sludge is fixed or contained in the inert solidification matrix, which is more suitable for the treatment of oil sludge containing CaCl2, Na Cl, and the treatment of sludge with low oil content.
At present, the cement curing agent is generally used for curing, which can meet the requirements of safe land landfill treatment. The efficiency of solidification treatment is high, and it can also be used as a resource after treatment. However, the properties of oily sludge in each oil and gas field are different, so the targeted development and use of the solidification agent is an important research direction.

2.2.2 microbiological treatment
Biological treatment refers to the use of microorganisms to degrade and mineralize oily sludge and ultimately transform it into harmless inorganic substances. The factors that affect the treatment effect include the following.

1) Species and number of microorganisms.
2) The growth environment of microorganisms, such as moisture content, temperature, and oxygen concentration of nutrients.
3) Biochemical characteristics of pollutants. Different microorganisms have different degradation ability to oily sludge. At the same time, a variety of microorganisms or strains mixed often can play a more ideal degradation effect.
Secondly, the final product of microbial treatment is water, carbon dioxide, and other harmless substances, which will not cause secondary pollution to the environment, and will not lead to pollutant transfer, and the cost is not high, which is an important research direction of oil sludge harmless treatment.

2.3 resource processing

2.3.1 pyrolysis
In the anoxic environment, the organic matter in oily sludge can be decomposed into solid carbon, liquid fuel oil, etc., which are all reusable resources. It is found that the treatment of oily sludge by pyrolysis can recover oil and gas more effectively, redevelop the utilization value of residue, and have better benefits.

2.3.2 coking
Coking treatment is a technology to realize high temperature cracking or heat shrinking by the coking reaction of residual oil and heavy oil. According to the actual situation of various oil and gas fields, there are mainly two ways to coking oily sludge.

1) Firstly, the oily sludge is dehydrated, then mixed with a suitable catalyst, and put into the coking reactor to realize the coking reaction. After condensation and cracking, the noncondensable gas, conversation, and liquid-phase oil products are produced.
2) A proper amount of carbonation additive and strength additive is added to the oily sludge, and then the carbon-containing adsorbent and other products are produced through the coking reaction.

2.3.3 solvent extraction

Solvent extraction refers to the use of extractant to dissolve oily sludge, after stirring and centrifugation, the use of extractant to extract oil and organic matter and then re-refining to produce usable fuel oil. The recovery distillation technology can also recycle the extractant.
However, it should be noted that the extractant usually needs to be used together with other technologies to achieve an ideal recovery effect, such as combined use with dispersant, mechanical agent, and low-frequency acoustic wave.

3. Prospect of oil sludge treatment technology in oil and gas fields

At present, the treatment of oily sludge in foreign countries has been more advanced and developed, but in China, it is still in its infancy, many experiments are still in the laboratory research stage, and there is a lack of typical demonstration projects. At the same time, most of the research focuses on the recovery of crude oil from oily sludge, but the research on the purification technology of oily sludge is also limited.

Although it is relatively simple to make sludge cake or landfill, it will cause certain economic loss and environmental pollution. The treatment of oily sludge with various additives needs to pay a high cost, and part of the treatment will also cause secondary pollution. Although the operation cost of biological treatment is low and energy is saved, waste residue treatment is also a problem.

With the continuous improvement of oily sludge treatment technology, biochemistry, physics- The application of combined technologies such as chemistry will become a major direction of oily sludge treatment in oil and gas fields. At the same time, the composition of oily sludge is relatively complex, and the oily sludge in each oil and gas field has its own characteristics. According to the actual situation of oil and gas fields, the oily sludge will be classified and treated in stages, and finally, the harmless treatment and resource utilization of oily sludge will be realized, which is also the main research in the future Direction.