Summary
Production of hydrocarbons is usually accompanied by the production of
water. This produced water consists of formation water and/or water that has
previously been injected into the formation. As more oil is produced, the
amount of produced water increases. Unfortunately, the produced water is not a
saleable product; hence an operator must find ways to handle relatively large
amounts of water in an environmentally-acceptable manner at the lowest cost.
One way of managing this water is to re-inject it for disposal, pressure
maintenance, or enhanced oil recovery. An important and difficult task in the
re-injection process is the prediction of the impact of water quality on well
injectivity. This is mainly because of the poor understanding of the deposition
mechanisms by which suspended solids and oil droplets present in the produced
water are retained by the formation.
As part of a study on formation damage, different concentrations of hematite
particles suspended in water were injected into sandstone core samples at
residual oil saturation. The theories of deep-bed filtration are evaluated. The
effects of residual oil on the filtration coefficient λ and the
formation damage factor β are examined. The presence of oil caused
greater apparent damage (reduction of permeability). It was also observed that
there is rather deeper invasion at residual oil saturation than at full brine
saturation.
Introduction
Produced water containing oil in the range of 500 mg/l to 5000 mg/l or
higher is usually treated before reinjection for two reasons. First of all, the
oil in the injection water may cause damage to the formation, hence the oil
content of the injection fluid must be reduced to a suitable level before use
for reinjection. Secondly, the oil that is recovered from the produced water is
routed to the oil sales meter to generate cash for the operation, (Thro et al.
1997; Van der Zande 2000; Janssen 2000). Nevertheless, some oil will always
remain in the injection water. Over time, oil will accumulate around the
wellbore and form an oil-bank in which there is residual oil saturation. Thus,
it is very relevant to discuss the effect of this residual oil on the
injectivity of the well.
Several researchers tried to study deep-bed filtration on cores that are
100% saturated with brine while injecting suspended particles or oily-water, or
a combination of both, but very few (Hsi et al. 1994; Colman and McLelland
1994) have tried injecting suspended particles into cores at residual oil
saturation. In this study, an online single detector x-ray system was used to
examine deep-bed filtration during water injection in sandstone cores at
residual oil saturation. Hematite particles were suspended in the brine at
different concentrations. Such cores were used to more closely approximate the
conditions and wettability effects in the region around a wellbore.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
6 March 2007
- Meeting paper published:
30 May 2007
- Revised manuscript received:
26 May 2008
- Manuscript approved:
19 June 2008
- Published online:
2 March 2009
- Version of record:
26 February 2009
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