Summary
The ionic strength of injection water can have a major impact on oil
recovery resulting from the use of low-salinity brines. Understanding how the
water and oil chemistry affects the final recovery from a physicochemical point
of view is necessary in order to optimize low-salinity waterflooding. It is
clear from the literature that wettability is a key factor in achieving the
low-salinity effect. Optimum ionic strength and conditions for low-salinity
flooding with respect to wettability are still uncertain.
In this paper, we studied fluid/rock interactions at different salinity
levels and elevated temperature conditions in terms of wettability and surface
charge. Wettability is determined by a high-temperature/high-pressure (HT/HP)
contact-angle method and zeta-potential technique. Outcrop rocks and stock-tank
crude-oil samples were used in all experiments. Synthetic formation brines,
aquifer, and seawater were evaluated under high-pressure conditions. Zeta
potential of sandstone rocks and selected clay minerals was measured as a
function of ionic strength.
Wettability of oil/brine/sandstone systems depends on salinity, temperature,
and rock mineralogy. Using aquifer water in Berea sandstone improved the
wettability toward water-wet condition. The same aquifer water behaved in a
different way when a different sandstone surface was tested. In Scioto
sandstone, aquifer water changed the wettability to neutral state. Low-salinity
water expanded the double-layer thickness and eventually increased the
zeta-potential magnitude. As a result of this expansion, it provides a greater
opportunity to alter the wettability and enhance oil recovery. This study
indicates that clay content in sandstone rocks can significantly alter the
wettability either toward water-wet or intermediate. On the basis of the
results obtained from this study, it is clear that low-salinity waterflooding
can improve oil recovery in the field.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
16 September 2010
- Meeting paper published:
3 May 2010
- Revised manuscript received:
9 February 2011
- Manuscript approved:
1 June 2011
- Published online:
12 December 2011
- Version of record:
28 December 2011
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