Volume-Translated, Modified Peng-Robinson Equation of State for Coalbed Gas/Water Mixtures

Monday, October 17, 2011
Exhibit Hall B (Minneapolis Convention Center)
A. M. Abudour, S.A. Mohammad, R.L. Robinson Jr. and K. A. M. Gasem, School of Chemical Engineering, Oklahoma State University, Stillwater, OK

Simulations of enhanced coalbed methane (CBM) recovery and CO2 sequestration operations require reliable phase equilibrium models capable of describing accurately the vapor-liquid equilibria (VLE) behavior and the phase densities of coalbed gases (methane, nitrogen and CO2) and water. A suitable model needs to be applicable over the range of conditions encountered in coalbed reservoirs, which are near-critical or supercritical. Our recent studies have indicated that the modified Peng-Robinson equation of state (MPR EOS) provides good representation of the phase behavior of these systems. Moreover, when equipped with volume translation and scaling-law behavior correction, the MPR EOS is capable of predicting volumetric properties of the individual CBM components within 2% absolute average deviation.

 In this work, the MPR EOS with volume translation and scaling-law behavior correction was extended to mixtures for the prediction of phase densities comprised of mixtures of methane, nitrogen, CO2 and water. The volume-translation and scaling correction to the EOS has yielded satisfactory predictions for the mixtures. To further validate the MPR EOS, the phase densities of selected mixtures were measured experimentally on a volumetric apparatus and the EOS was tested with the newly acquired data.

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