Reduced Phase Equilibrium Calculations: New Reduced Parameters, Critical Analysis And Fluid Characterization

Open Access
Author:
Gorucu, Seyhan Emre
Graduate Program:
Petroleum and Natural Gas Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 29, 2013
Committee Members:
  • Russell Taylor Johns, Dissertation Advisor
  • Russell Taylor Johns, Committee Chair
  • Turgay Ertekin, Committee Member
  • Yilin Wang, Committee Member
  • Christopher Griffin, Committee Member
Keywords:
  • flash calculations
  • phase behavior
  • stability analysis
  • phase equilibrium calculations
  • solution of nonlinear equations
  • Newton's method
  • Newton-Raphson
  • Minimization
  • fluid characterization
Abstract:
Phase equilibrium calculations constitute a significant percentage of computational time in compositional simulation, especially as the number of components and phases increases. Reduced methods address this problem by carrying out phase equilibrium calculations using a reduced number of independent parameters. Some researchers have found that reduced methods speed up flash calculations, decrease simulation times, and also improve robustness. We propose new reduced parameters using the two-parameter binary interaction parameter (BIP) formula originally proposed by Li and Johns (2006). We implement the new reduced parameters to two- and three-phase equilibrium calculations. We compare the new reduced two-phase flash calculations with several reduced and conventional techniques in terms of robustness and speed. The new reduced two-phase flash calculations show improved robustness with similar speed as the fastest reduced flash calculations. The new algorithm is also shown to be significantly faster than the conventional methods. We further critically analyze several proposed reduced algorithms and explain why some of the reduced techniques are slower than others. We further compare our new reduced multiphase equilibrium calculations with the reduced multiphase equilibrium calculations of Okuno et al. (2010a). Our results show that the improved robustness in our two-phase flash calculations becomes more significant in the three-phase region indicating a larger radius of convergence. We have also observed that our three-phase flash calculations converge to the correct solution more often than the other reduced technique. Reduced methods may improve accuracy when many components and phases are used in phase equilibrium calculations. Reduced methods, however, may not be able to fit the exact BIPs determined from conventional cubic EOS characterizations. Therefore, one of the remaining questions is accuracy. We carry out fluid characterization steps in a suitable manner for reduced phase equilibrium calculations. We show that for the fluids studied, reduced parameters estimate the experimental data well without compromising speed during phase behavior calculations.