SPE Journal
Volume 15,
Number 3,
September 2010,
pp. 689-703
Summary
CO2 flooding at low temperatures often results in three or more
hydrocarbon phases. Multiphase compositional simulation must simulate such
gasfloods accurately. Drawbacks of modeling three hydrocarbon phases are the
increased computational time and convergence problems associated with flash
calculations. Use of a reduced method is a potential solution to these
problems.
We first demonstrate the importance of using three-phase flash calculations
in compositional simulation by investigating difficulties with two-phase
equilibrium approximations proposed in the literature. We then extend an
algorithm for reduced two-phase flash calculations to three-phase calculations
and show the efficiency and robustness of our algorithm. The reduced
three-phase flash algorithm is implemented in a multiphase compositional
simulator to demonstrate the speed-up and increased robustness of simulations
in various case studies.
Results show that use of a two-phase equilibrium approximation in reservoir
simulation can result in a complete failure or erroneous simulation results.
Simulation case studies show that our reduced method can decrease computational
time significantly without loss of accuracy. Computational time is reduced
using our reduced method because of the smaller number of equations to be
solved and increased timestep sizes. We show that a failure of a flash
calculation leads directly to reduced timestep sizes using the UTCOMP
simulator.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
30 July 2009
- Revised manuscript received:
9 September 2009
- Manuscript approved:
29 September 2009
- Published online:
7 April 2010
- Version of record:
22 September 2010
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