Oil extraction is an indispensable basic link in the modern industrial system, but its accompanying “by-product” – oilfield wastewater, is also a serious environmental problem. Oilfield wastewater usually includes produced water, injection water flowback, drilling fluid residue and surface facility cleaning water. Its composition is complex, with high oil content, concentrated suspended matter, high salinity, and may contain heavy metals, organic pollutants and radioactive substances. It is a typical high-difficulty industrial wastewater.
Driven by the “dual carbon” strategy and the concept of green and low-carbon development, oilfield companies are facing unprecedented environmental pressure. How to effectively control and manage wastewater discharge while ensuring the stable operation of energy production has become a key proposition for the green transformation of the oil industry.
Composition characteristics and treatment difficulties of oilfield wastewater
2.1 Complex composition
The main characteristics of oilfield wastewater are as follows:
High oil content: including emulsified oil, dispersed oil and dissolved oil.
High solid content: a large amount of suspended solids such as mud, sand, drill cuttings, clay, humus, etc.
High salinity: especially formation return water, often contains high concentrations of inorganic salts such as sodium chloride and sodium sulfate.
Organic pollutants: such as chemical additives such as surfactants, scale inhibitors, and bactericides.
High volatility: the composition of wastewater varies greatly under different oil wells, mining stages, and injection and production methods.
2.2 Difficulties in treatment
Emulsified oil is stable and difficult to separate;
Solid-liquid mixture, wide range of particle size;
High viscosity, high temperature, corrosive components;
Improved emission standards (especially COD, oil, SS indicators);
Traditional sedimentation and filtration processes are inefficient and have high operating costs.
This requires that oilfield wastewater treatment equipment must have extremely strong separation performance, corrosion resistance, automatic control capabilities and adaptive adjustment capabilities.
Technical principle and adaptability analysis of horizontal screw centrifuge
Overview of working principle
Horizontal screw centrifuge is a continuous operation equipment that uses centrifugal force field for solid-liquid separation. Its core structure includes drum, screw conveyor, differential, drive device and control system.
The working process is as follows:
Oil-containing sewage enters the high-speed rotating drum;
Use centrifugal force to separate oil, water and solid particles with different densities;
The screw conveyor continuously pushes out the solids deposited on the inner wall of the drum at a certain differential speed;
The clear liquid flows out from the other end or multiple outlets to achieve three-phase or two-phase separation.
By reasonably adjusting the drum speed, differential speed, pitch and centrifugal force, the separation process can be finely controlled to improve the processing accuracy.
Application scenarios of decanter centrifuge in oilfield wastewater treatment
Produced water treatment
The produced water in the oil production process contains crude oil, silt, bacteria, etc. The decanter centrifuge can efficiently separate the three phases of oil, water and solid, providing a good foundation for subsequent fine treatment.
Case reference: A certain oil field in the Middle East uses a decanter centrifuge to treat 3000m³ produced water per day, reducing the oil content to below 30ppm, and the SS removal rate exceeds 90%, meeting the re-injection standard.
Surface equipment cleaning water treatment
Drilling equipment and storage tank cleaning process produces a large amount of oily wastewater and high-concentration mud. The decanter centrifuge can effectively dehydrate and reduce the volume, reducing the burden of subsequent treatment.
Oil sludge treatment and reduction
Oil sludge is a by-product of wastewater treatment sedimentation or flotation process. It has a high oil content and a large amount of water, which is difficult to directly incinerate or landfill. The decanter centrifuge can dehydrate it to a water content of about 40%, greatly reducing the volume, which is convenient for subsequent incineration or resource utilization.
Typical application: A certain oil field in Northwest China uses a horizontal screw centrifuge to dehydrate oil sludge, which reduces the transportation cost by about 200 yuan per ton of oil sludge. The residual oil after treatment can be recycled and reused, and the annual comprehensive benefits are significantly improved.
As a mature and continuously innovative solid-liquid separation technology, the decanter centrifuge is playing an increasingly critical role in the field of oilfield wastewater treatment. It not only helps enterprises achieve pollution reduction, resource recovery and cost control, but also plays the role of a “behind-the-scenes hero” in promoting the sustainable development and green and low-carbon goals of oilfields.
