Summary
Recently, it has been shown that the presence of residual oil in a formation
can have a considerable influence on the trapping mechanisms for particles
present in reinjected produced water (Ali 2007; Ali et al. 2005, 2007, 2009).
This article reports on a further set of extensive coreflow experiments that
confirm and extend these results. The tests were conducted in a
computerized-tomography (CT) scanner, allowing direct observation of the
buildup of particle deposition along the core.
These experiments are relevant to operational issues associated with
produced-water reinjection (PWRI). In many cases, produced water is injected
into formations containing oil, so reduced oil saturation is achieved rapidly
in the area around the well. Even if the well is outside the oil zone, trapped
oil droplets are always present in produced water, and a residual-oil zone will
gradually build up around the well.
Major differences are found between the deposition profiles for fully
water-saturated cores and the cores having residual-oil saturation. In
particular, particles penetrate deeper into the core with residual-oil
saturation, and considerably more particles pass completely through the core
without being trapped. The X-ray technique allows direct observation during the
experiment of the deposition process inside the core, eliminating the
complicating effect of any external filter cake. As a result, an analysis can
be performed of the deposition parameters relevant inside the core using
deep-bed-filtration theory, and the results of this analysis are presented. In
particular, it is shown that the values of the filtration function determined
from the CT-scan (X-ray) data are consistent with those obtained from analysis
of the effluent concentration. Moreover, both methods of analysis find quite
clearly that the filtration coefficient increases with decreasing flow
rate.
The results indicate that formation damage near a wellbore during water
injection will be reduced by the presence of residual oil, and that particles
will penetrate deeper into the formation. The result is also relevant to
injection under fracturing conditions because particle deposition in the wall
of the fracture (where residual oil may be present) is one of the mechanisms
governing fracture growth.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
28 March 2009
- Meeting paper published:
28 May 2009
- Revised manuscript received:
16 December 2009
- Manuscript approved:
15 January 2010
- Published online:
8 July 2010
- Version of record:
2 December 2010
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