Summary
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.
Introduction
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).
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
25 October 2005
- Revised manuscript received:
1 May 2007
- Manuscript approved:
16 May 2007
- Version of record:
20 September 2007
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