Experimental Research on Treatment of Produced Water From a Polymer-Flooding Process Using a Double-Cone Air-Sparged Hydrocyclone
- Shumeng Liu (Shanghai Jiaotong University) | Xuefeng Zhao (Daqing Oilfield Co. Ltd.) | Xigui Dong (Daqing Oilfield Co. Ltd.) | Baolin Miao (Daqing Oilfield Co. Ltd.) | Wei Du (Daqing Oilfield Co. Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Projects, Facilities & Construction
- Publication Date
- September 2007
- Document Type
- Journal Paper
- 1 - 5
- 2007. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 5.2.1 Phase Behavior and PVT Measurements, 5.4 Enhanced Recovery, 4.5 Offshore Facilities and Subsea Systems, 5.4.1 Waterflooding, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.2 Pipelines, Flowlines and Risers, 5.1 Reservoir Characterisation, 5.3.2 Multiphase Flow, 4.1.5 Processing Equipment, 3.2.6 Produced Water Management
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Produced water from polymer flooding (polymer-produced water) is difficult to treat by the conventional gravity settling process. A new type of double-cone air-sparged hydrocyclone (DcASH) has been designed, and its fundamental structure and operating principles are introduced in this paper. Experimental research on treating produced water from polymer flooding has been carried out, showing that the DcASH has a high treatment capacity. The oil concentration of treated water was less than 100 mg/L, which satisfied the requirements of the next deep-bed filtration process stage. Compared to gravity settling, conventional hydrocyclones, and flotation, the DcASH has a higher separation efficiency, which indicates that DcASH will have good application prospects in oilfield produced-water treatment.
In crudeoil extraction, water can be injected into the stratum to drive the crude oil out of the ground, which is often called a waterflooding process. The oil content decreases after waterflooding has been performed for some time. To improve oil recovery, polymer flooding (use of injected water containing polymer), which is often called enhanced oil recovery (EOR) (Wang et al. 1999), could sometimes be used. Polymer flooding technology has been widely used in the Daqing oil field in China in recent years. Oil production by polymer flooding in Daqing oil field reached 10 million tons in 2003, which was about one-quarter of the total annual oil production from the field (Wang and Liu 2004; Wang et al. 2005).
Because most of the polymer remains in the produced water, the viscosity of the wastewater is high and the oil droplets in it are very small. As a result, the produced water from polymer flooding is more difficult to treat than that from waterflooding. The conventional gravity settling process has not been able to meet the requirement for polymer-produced-water treatment in the Daqing oil field (Luo et al. 2003; Jing et al. 2004). To improve treated water quality, the total settling time has been extended to 12 hours, while for produced water from waterflooding, the settling time is 6 hours. It is therefore crucial to develop effective technologies to treat polymer-flooding wastewater.
The air-sparged hydrocyclone (ASH) is a type of separating device that intensifies its operating effect by means of centrifugal force. The ASH has been used in fine mineral particle flotation and pulp and paper wastewater flotation since it was invented by Miller in the early 1980s. The concept of ASH for fine particle flotation is based on the proposition that the energy of the inertial collision between a fine particle and an air bubble will be increased sufficiently in a strong centrifugal-force field to achieve film rupture, bubble attachment, and flotation. In ASH, the centrifugal-force field is generated by conversion of pressure head into the rotational motion of swirl flow. The ASH design has a cylindrical geometry with two tangential or involute feed entries at the top. It consists of two concentric vertical tubes, a conventional buffer chamber header at the top, and a froth pedestal at the bottom. The basic structure of a DcASH is shown in Fig. 1. The inner tube is a porous tube through which air is sparged. The outer nonporous tube serves as an air jacket. The inner and outer tubes form an air chamber to provide for the even distribution of air through the inner porous tube. The froth pedestal support at the bottom forms an annular opening through which the underflow discharges. Flotation is accomplished when the particulate suspension enters through the tangential inlet at the top of the ASH and follows a helical path before exiting in swirl flow through the underflow opening. During flow through the unit, collisions between centrifuged particles and air bubbles take place, bubble attachment to hydrophobic particles occurs, and the bubble-hydrophobic particle aggregate is transported along with the froth toward the vortex finder into the overflow stream. This high-speed swirl flow exerts a considerable shear force at the inner porous tube wall. This, coupled with the fact that the air is introduced through small pores, results in the generation of a large number of small air bubbles, which facilitates the flotation of fine hydrophobic particles (Das and Miller 1996; Das and Miller 1995; Miller et al. 1988; Miller et al. 1993; Miller and Das 1994).
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