A New Equation of State of State for Better Liquid Density Prediction of Natural Gas Systems.

Open Access
Author:
Nwankwo, Princess Christiana
Graduate Program:
Petroleum and Natural Gas Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 15, 2014
Committee Members:
  • Michael Adebola Adewumi, Dissertation Advisor
  • Michael Adebola Adewumi, Committee Chair
  • Turgay Ertekin, Committee Member
  • Mku Thaddeus Ityokumbul, Dissertation Advisor
  • Zhibiao Zhao, Committee Member
Keywords:
  • Equation-of-State
  • Thermodynamic properties
  • Phase behavior
  • Natural Gas
  • Gas Compressibility Factor
  • Liquid Densities
Abstract:
The sustained, almost unrelenting excitement in the frontiers of Equations of state (EOS), research which includes their modifications and/or new developments, has been borne out of the need for better reservoir fluid understanding and thermodynamic characterization. Equations of state methods are far less expensive (in terms of material cost and time) than laboratory or experimental forages and the results are interestingly not too far removed from the limits of acceptable accuracy. In most cases, the degree of accuracy obtained, by using various EOS’s, though not appreciable, have been acceptable when considering the gain in time. The possibility of obtaining an equation of state which though simple in form and in use, could have the potential of further narrowing the present existing bias between experimentally determined and popular EOS estimated results spurred the interest that resulted in this study. This research study had as its chief objective, to develop a new equation of state that would more efficiently capture the thermodynamic properties of gas condensate fluids, especially the liquid phase density, which is the major weakness of other established and popular cubic equations of state. The set objective was satisfied by a new semi analytical cubic three parameter equation of state, derived by the modification of the attraction term contribution to pressure of the van der Waal EOS without compromising either structural simplicity or accuracy of estimating other vapor liquid equilibria properties. The application of new EOS to single and multi-component light hydrocarbon fluids recorded far lower error values than does the popular two parameter, Peng-Robinson’s (PR) and three parameter Patel-Teja’s (PT) equations of state. Furthermore, this research was able to extend the application of the generalized cubic equation of Coats (1985) to three parameter cubic equations of state, a feat, not yet recorded by any author in literature.