Summary
Laboratory data on water-alternating-gas (WAG) injection for non-water-wet
systems are very limited, especially for near-miscible (very low IFT) gas/oil
systems, which represent injection scenarios involving high-pressure
hydrocarbon gas or CO2 injection. Simulation of these processes
requires three-phase relative permeability (kr) data. Most of
the existing three-phase relative permeability correlations have been developed
for water-wet conditions. However, a majority of oil reservoirs are believed to
be mixed-wet and, hence, prediction of the performance of WAG injection in
these reservoirs is associated with significant uncertainties. Reliable
simulation of WAG injection, therefore, requires improved relative permeability
and hysteresis models validated by reliable measured data.
In this paper, we report the results of a comprehensive series of coreflood
experiments carried out in a core under natural water-wet conditions. These
included water injection, gas injection, and also WAG injection. Then, to
investigate the impact of wettability on the performance of these injection
strategies, the wettability of the same core was changed to mixed-wet (by aging
the core in an appropriate crude oil) and a similar set of experiments were
performed in the mixed-wet core. WAG experiments under both wettability
conditions started with water injection (I) followed by gas injection (D), and
this cyclic injection of water and gas was repeated (IDIDID).
The results show that in both the water-wet and mixed-wet cores, WAG
injection performs better than water injection or gas injection alone. Changing
the rock wettability from water-wet to mixed-wet significantly improves the
performance of water injection. Under both wettability conditions (water-wet
and mixed-wet), the breakthrough (BT) of the gas during gas injection happens
sooner than the BT of water in water injection. Ultimate oil recovery by gas
injection is considerably higher than that obtained by water injection in the
water-wet system, while in the mixed-wet system, gas injection recovers
considerably less oil.
© 2013. Society of Petroleum Engineers
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History
- Original manuscript received:
6 July 2011
- Meeting paper published:
6 September 2012
- Revised manuscript received:
30 January 2012
- Manuscript approved:
7 March 2012
- Published online:
25 January 2013
- Version of record:
27 February 2013
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