SPE Journal
Volume 16, Number 4, December 2011, pp. 743-750

SPE-129709-PA

Limitations of Current Method-of-Characteristics (MOC) Methods Using Shock-Jump Approximations To Predict MMPs for Complex Gas/Oil Displacements

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DOI  More information 10.2118/129709-PA http://dx.doi.org/10.2118/129709-PA

Citation

  • Ahmadi, K., Johns, R.T., Mogensen, K., and Noman, R. 2011. Limitations of Current Method-of-Characteristics (MOC) Methods Using Shock-Jump Approximations To Predict MMPs for Complex Gas/Oil Displacements. SPE J.  16 (4): 743-750. SPE-129709-PA. http://dx.doi.org/10.2118/129709-PA.

Discipline Categories

  • 6.2.2 Fluid Modeling, Equations of State
  • 6.2.1 Phase Behavior and PVT Measurements
  • 6.4.2 Gas-Injection Methods
  • 6.4.7 Miscible Methods

Keywords

  • MMP, MOC, Method of Characteristics, Mixing cell, Miscibility

Summary

An accurate minimum miscibility pressure (MMP) is one of the key factors in miscible-gasflood design. There is a variety of experimental and analytical methods to determine the MMP, but the most-reliable methods are slimtube experiments, 1D slimtube simulations, mixing-cell models, and the fast key-tie-line approach using the method of characteristics (MOC). Direct comparisons of all these methods generally agree well, but there are cases in which they do not. No explanation has yet been given for these anomalies, although the MMP is critically important to recovery.

The focus of this paper is to explain when current MOC results assuming that shocks exist from one key tie line to the next may not be reliable, and how to identify when this is the case. We demonstrate, using fluid characterizations from Middle East oils, that the MMPs using this MOC method can be more than 6.500 psia greater than those calculated using a recently developed mixing-cell method. The observed differences in the MMP increase substantially as the API gravity of the oil decreases, likely the result of the onset of L1-L2-V behavior. We show that the key tie lines determined using this MOC method do not control miscibility for such cases. We explain the reasons for these differences using simplified pseudoternary models and show how to determine when an error exists. We also offer a way to correct the MMP predictions using the MOC for these complex gas/oil displacements without solving for the complete compositional path.

© 2011. Society of Petroleum Engineers

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History

  • Original manuscript received: 31 May 2010
  • Meeting paper published: 25 April 2010
  • Revised manuscript received: 23 April 2011
  • Manuscript approved: 3 May 2011
  • Published online: 25 October 2011
  • Version of record: 23 December 2011