Most of the oilfields in our country are exploited by water injection (water injection fracturing). Each ton of source oil is produced by water injection of about 2-3 tons. Therefore, in the source oil exploitation, the production wastewater also enters the gathering and transportation system with the source oil.

In the later stage of production, the water cut of source oil can be as high as 90% Oilfield wastewater can only be reinjected into the formation after treatment. Let's learn about the common treatment methods of oilfield wastewater.

To solve the problem of oilfield industrial wastewater, we must first understand the source and characteristics of Oilfield Industrial Wastewater: oilfield wastewater comes from drilling, oil production, well flushing and other processes in oil and gas exploitation. Therefore, the composition of oilfield wastewater is complex. It is a mixture of organic and inorganic, and it also involves the distribution of organic matter in water and oil phases, through steam thermal recovery, tertiary oil recovery and other treatment processes After that, gum asphaltene, fatty acids, mercaptans and other substances in the oil enter the water phase in a certain form under certain conditions, which makes the relative composition of organic matter in water and oil change greatly.

Fatty acids and glial asphaltenes in oil are natural emulsifiers. They form emulsified oil with oil in the process of thermal recovery, tertiary oil recovery and stratum migration. Therefore, the oil in wastewater mainly exists in the form of emulsified oil and free oil. After oil-water separation in the settlement station, a considerable part of oil remains in the water phase.

Because of the complex composition of organic and inorganic matters in the water, it is difficult to treat oilfield wastewater. Although the water quality of each oil field is different, it generally appears to have the following characteristics:

The high degree of mineralization accelerates the corrosion rate and makes the biochemical treatment of wastewater difficult;

The oil content is high, which is far greater than the water quality standard required by various outlets;

It contains a large number of microorganisms, which not only corrode the pipeline, but also cause serious formation plugging;

There are a lot of scaling ions in the produced water, such as SO42 -, CO32 -, Ca2 +, Mg2 +, Ba2 +, etc;

The content of suspended solids (polymer in polymer injection area) is high and the particles are small, which is easy to cause formation plugging. Harm of oilfield wastewater

A lot of wastewater will be produced in the process of oilfield exploitation, especially in large-scale oilfield exploitation. The water content of produced fluid is relatively higher. Oilfield waste water is a complex liquid mixture, its main components are water, source oil, soluble gas, solid suspension, electrolyte, bacteria and various oilfield chemical additives and other substances. Direct discharge will not only cause serious harm to the environment, but also pollute surface water and farmland, resulting in the death of animals and plants and potential human diseases, causing serious harm to the life of local people 。 Moreover, the acid gas or salt in oilfield wastewater will accelerate the corrosion of pipeline equipment; the solid suspension in oilfield wastewater will block the formation; the industrial bacteria in oilfield wastewater will corrode and block the pipeline, and make the water quality worse.