Summary
Preformed particle gel (PPG) has been successfully synthesized and applied
to control excess water production in most of the mature, waterflooded oil
fields in China. This paper reports on laboratory experiments carried out to
investigate PPG transport mechanisms through porous media. Visual observations
in etched-glass micromodels demonstrate that PPG propagation through porous
media exhibits six patterns of behavior: direct pass, adsorption, deform and
pass, snap-off and pass, shrink and pass, and trap. At the macroscopic scale,
PPG propagation through porous media can be described by three patterns: pass,
broken and pass, and plug. The dominant pattern is determined by the pressure
change with time along a tested core (as measured at specific points), the
particle-size ratio of injected and produced particles from the core outlet,
and the residual resistance factor of each segment along the core. Measurements
from micromodel and routine coreflooding experiments show that a swollen PPG
particle can pass through a pore throat with a diameter that is smaller than
the particle diameter owing to the elasticity and deformability of the swollen
PPG particle. The largest diameter ratio of a PPG particle and a pore throat
that the PPG particle can pass through depends on the swollen PPG strength. PPG
particles can pass through porous media only if the driving pressure gradient
is higher than the threshold pressure gradient. The threshold pressure depends
on the strength of the swollen PPG and the ratio of the particle diameter and
the average pore diameter.
Introduction
Reservoir heterogeneity is a principle factor responsible for the low sweep
efficiency of injected water or gas. To control conformance in waterflooding or
gasflooding, many technologies have been applied, such as polymer flooding,
foam flooding, alkaline-surfactant-polymer (ASP), and so on (Wang et al. 2003;
Song et al. 1995; Grigg and Schechter 1997). Injecting a large volume of gel to
correct in-depth permeability for those reservoirs with fractures or channels
has been an attractive technology for years (Sydansk and Southwell 2000; Lane
and Seright 2000; Wang et al. 2001; Fielding et al. 1994; Bai et al. 1999). In
this paper, “channel” means a super-high-permeability zone or streak; it does
not mean flow through a common matrix.
In recent years, the study of preformed gel for conformance control has
gained great interest among gel-based enhanced-oil-recovery processes. Seright
(1997, 2000) studied the behavior of preformed bulk gel through fractures and
demonstrated that preformed bulk gel had better placement than in-situ gel and
could effectively reduce gel damage on unswept low-permeability oil zones or
matrix (Seright 1997, 2000, 2003; Chauveteau et al. 2000, 2001). Chauveteau et
al. (2000, 2001, 2003) synthesized preformed microgel particles that were
crosslinked under shear; Feng et al. (2003) demonstrated that the microgels
could be easily injected into porous media without any sign of plugging, and
that these microgels should be good candidates for water-shutoff and
profile-control operations.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
12 January 2004
- Meeting paper published:
17 April 2004
- Revised manuscript received:
17 December 2006
- Manuscript approved:
20 December 2006
- Version of record:
20 April 2007
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