Multiple mixing-cell method for MMP calculations

Kaveh Ahmadi, Russell T. Johns

Research output: Chapter in Book/Report/Conference proceedingConference contribution

15 Scopus citations

Abstract

The minimum miscibility pressure (MMP) is a key parameter governing the displacement efficiency of gas floods. There are several methods to determine the MMP, but the most accurate methods are slim-tube experiments, analytical methods, and numerical simulation/cell-to-cell methods. Slim-tube experiments are important to perform because they use actual crude oil, but they are costly and time consuming. Analytical methods use the method of characteristics (MOC), are very fast, and help to understand the structure of gas floods. MOC, however, relies on finding the unique and correct set of key tie lines in the displacements, which can be difficult. Slim-tube simulation methods and their simplified cell-to-cell derivatives can be slow and their MMP estimates clouded by dispersion. This paper presents a simple and accurate multiple mixing cell method for MMP calculations that corrects for dispersion, and is substantially faster than simulation methods. Unlike previous "mixing cell" methods, our cell-to-cell mixing model uses a variable number of cells, and is independent of gas-oil ratio, volume of the cells, excess oil volumes, and the amount of gas injected. The new method relies on robust P-T flash calculations using any cubic equation-of-state (EOS). The calculations begin with only two cells and performs additional cell to cell contacts between resulting equilibrium phase compositions based on which phase has a greater mobility. For two-phase vapor-liquid equilibrium, we assume the vapor moves ahead of its equilibrium liquid. We show for a variety of oil and gas compositions that all key tie lines can be found to the desired accuracy, and that they are nearly identical to those found using analytical MOC methods. Our approach, however, is more reliable and robust than those from MOC because we do not need to approximate nontie-line paths by shocks, and the unique set of key tie lines converge automatically. The MMP using our mixing cell method is estimated from four or five pressure calculations based on a power-law extrapolation of the smallest tie line to zero length. We show through an example that the assumed relative value of the phase mobilities can affect the MMP, which has important implications for the MMP of three-phase liquid hydrocarbon systems. Our multiple mixing cell method can calculate either the MMP or the minimum miscibility for enrichment (MME) independent of the number of components in the gas or oil.

Original languageEnglish (US)
Title of host publicationSPE Annual Technical Conference and Exhibition, ATCE 2008
Pages4943-4953
Number of pages11
StatePublished - Dec 1 2008
EventSPE Annual Technical Conference and Exhibition, ATCE 2008 - Denver, CO, United States
Duration: Sep 21 2008Sep 24 2008

Publication series

NameProceedings - SPE Annual Technical Conference and Exhibition
Volume7

Other

OtherSPE Annual Technical Conference and Exhibition, ATCE 2008
CountryUnited States
CityDenver, CO
Period9/21/089/24/08

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All Science Journal Classification (ASJC) codes

  • Fuel Technology
  • Energy Engineering and Power Technology

Cite this

Ahmadi, K., & Johns, R. T. (2008). Multiple mixing-cell method for MMP calculations. In SPE Annual Technical Conference and Exhibition, ATCE 2008 (pp. 4943-4953). (Proceedings - SPE Annual Technical Conference and Exhibition; Vol. 7).