Summary
In gas-injection enhanced oil recovery (EOR), simultaneous injection of
water and gas from parallel horizontal wells with water injected from the upper
well [sometimes called modified simultaneous water and gas (SWAG) injection],
can give deeper penetration of gas before gravity segregation than SWAG from
the same well. Most previous studies of this process were limited to 2D, in
which the injection rate is uniform along each well.
In 3D, we find that gas injection can be far from uniform, even in
homogeneous reservoirs--which are the focus of this study. If gas injection is
nonuniform in homogeneous reservoirs, it surely would be so in heterogeneous
reservoirs. In some cases, there is an inherent instability in uniform
injection along the gas well, even as the water well continues to inject nearly
uniformly along its length. In our results, the uniformity of gas injection
increases with increasing total injection rate and decreasing vertical distance
between gas- and water-injection wells. The instability leading to nonuniform
injection depends on the relation between gas saturation and gas relative
permeability; we speculate that effects of gas flow on hydrostatic pressure,
and therefore on gas-injection pressure, may also play a role. We find that in
some cases, lateral movement of gas from the injection point partially
mitigates the effects of nonuniform gas injection. Injecting gas from separate,
independent segments along the horizontal well improves sweep somewhat by
increasing the number of points at which gas exits the well.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
16 August 2008
- Meeting paper published:
4 December 2008
- Revised manuscript received:
14 March 2010
- Manuscript approved:
12 April 2010
- Published online:
5 August 2010
- Version of record:
24 August 2010
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