Summary
Solutions obtained by the method of characteristics (MOC) provide key
insights into complex foam enhanced-oil-recovery (EOR) displacements and the
simulators that represent them. Most applications of the MOC to foam have
excluded oil. We extend the MOC to foam flow with oil, where foam is weakened
or destroyed by oil saturations above a critical oil saturation and/or weakened
or destroyed at low water saturations, as seen in experiments and represented
in foam simulators. Simulators account for the effects of oil and capillary
pressure on foam using algorithms that bring foam strength to zero as a
function of oil or water saturation, respectively. Different simulators use
different algorithms to accomplish this.
We examine SAG (surfactant-alternating-gas) and continuous foam-flood
(coinjection of gas and surfactant solution) processes in one dimension, using
both the MOC and numerical simulation. We find that the way simulators express
the negative effect of oil or water saturation on foam can have a large effect
on the calculated nature of the displacement. For instance, for gas injection
in a SAG process, if foam collapses at the injection point because of infinite
capillary pressure, foam has almost no effect on the displacement in the cases
examined here. On the other hand, if foam maintains finite strength at the
injection point in the gas-injection cycle of a SAG process, displacement leads
to implied success in several cases. However, successful mobility control is
always possible with continuous foam flood if the initial oil saturation in the
reservoir is below the critical oil saturation above which foam collapses.
The resulting displacements can be complex. One may observe, for instance,
foam propagation predicted at residual water saturation, with zero flow of
water. In other cases, the displacement jumps in a shock past the entire range
of conditions in which foam forms. We examine the sensitivity of the
displacement to initial oil and water saturations in the reservoir, the foam
quality, the functional forms used to express foam sensitivity to oil and water
saturations, and linear and nonlinear relative permeability models.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
8 March 2009
- Meeting paper published:
12 June 2009
- Revised manuscript received:
25 December 2009
- Manuscript approved:
2 March 2010
- Published online:
19 August 2010
- Version of record:
15 March 2011
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