Abstract:
CO2 mixed with NGL is being evaluated as a method to enhance viscous oil
recovery from Schrader Bluff and other oil reservoirs at Milne Point, Alaska. The
sequestration of CO2 is a secondary objective of these proposed projects.
Mixtures of CO2 and NGL with the crude oil show a large three-phase
liquid-liquid-gas region, so three and four-phase flow may occur in the reservoir
when water is alternated with the miscible injectant. A compositional EOS simulator
has been used to simulate the oil recovery for both three-phase and four-phase flow
cases. The objective was to understand how important it is to simulate four-phase
flow rather than use a three-phase flow approximation. Two methods were used to model
three and four-phase relative permeabilities from two-phase relative permeabilities as
well as to evaluate the sensitivity of the results to the relative permeability
parameters. A two-dimensional vertical cross-section of the reservoir was modeled
with a stochastic permeability field to approximate heterogeneities. These simulations
clearly show that under these conditions, four-phase flow is significant. Four-phase
flow occurs over a significant part of the reservoir and affects both the sweep
efficiency and the injection and production rates when the wells are pressure
constrained and the production pressure corresponds to the three-phase region of the
phase diagram. The results are also very sensitive to the relative permeability
parameters regardless of which relative permeability model is assumed. The project
life is particularly sensitive to the relative permeability and is longer for
four-phase flow than predicted by a three-phase flow approximation because the relative
permeability of each phase is lower when four phases are modeled.
Reference:
B. Guler, P. Wang, M. Delshad, G. A. Pope and K. Sepehrnoori, "Three- and Four- Phase
Flow Compositional Simulations of CO2/NGL EOR," SPE 71485, Proceedings
of the SPE Annual Technical Conference and Exhibition, New Orleans, LA, 30 September - 3
October 2001.
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Last updated: April 25, 2002