Oilfield reinjection water is a method of treating produced water from oilfields as reinjection water, used in ballast water systems in the oil and gas industry to manage and treat produced water from oilfields. Produced water is extracted along with oil and gas during the production process. This water can be treated and reinjected into the oilfield for a variety of purposes – contributing to the storage, treatment, and reinjection of produced water, minimizing environmental impact, and optimizing the use of water resources.
Oilfield wastewater must be treated carefully before reinjection. The traditional treatment process is as follows: the oilfield produced water after oil-water separation of oily wastewater first enters the settling tank for natural settlement to remove most of the larger particles of suspended solids and oil, and then enters the high-efficiency separator such as air flotation, transverse flow or magnetic separation, and further removes suspended solids and oil in the wastewater by adding some flocculants, and then the wastewater after two purification processes enters the walnut shell filters, sand filters, and the secondary sand filters to carry out deep treatment. At this time, the effluent can only reach the A2 standard, that is, the oil content of ≤ 8 mg/L, suspended solids content of ≤ 3 mg/L, the median particle size of ≤ 2 μm. This traditional treatment process can remove most of the pollutants, but there is still a certain degree of emission problems.
At Daqing oilfield, it successfully reduced suspended solids, oil, and particles in the reinjection water to the standard of 1:1:1, without the use of external technologies such as ultrafiltration, which is the highest standard achieved in China.
The filter adopts multi-stage filtration, and the filtered water can be used for reinjection and discharge. The process of filtration is divided into 4 stages:
It adopts an automatic backwashing filter, which reduces the suspended matter and solid particles in the liquid to within 1 μm.
It uses an air flotation device to separate large oil particles into the liquid.
It uses a biochemical device to separate dissolved oil from the liquid.
It uses an ultrafiltration device, which can recycle the liquid.