Experimental Data and Eos Modeling for the Density of Natural Gas and Oil Constituents at Pressures to 40000 Psia and Temperatures to 500 °F

The production of petroleum fluids from very deep reservoirs requires accurate modeling of the fluid density and viscosity at pressures and temperatures (P-T) as high as 40000 psia and 500°F, respectively. Although correlations for the density of the components of natural gas and petroleum fluids are available in the literature, many of these equation-of-state correlations are based on a limited range of experimental data obtained at modest P-T conditions. We have initiated an experimental program to obtain density data that covers the entire P-T range of interest for deep reservoirs for model compounds including methane, propane, n-pentane, n-octane, iso-octane, cyclooctane, n-decane, n-hexadecane, and toluene. These density data, along with available literature data, are used to assess the performance of the SAFT, the perturbed chain SAFT (PC-SAFT), Peng-Robinson (PR), Soave-Redlich-Kwong (SRK), SRK with temperature-dependent volume translation, and the SRK with temperature- and density-dependent volume translation. The preliminary modeling results show that the PC-SAFT equation of state yields very low values of the percent average absolute deviation (AADP) of the density for each model component. For example, AADP values for the density of n-pentane, toluene, and n-decane are 0.82%, 0.59%, and 0.88%, respectively. The AADP obtained with the cubic equations of state are significantly larger; for n-pentane the AADP is 4.38% and 6.62% for the PR and the SRK, respectively. In contrast, the SRK with temperature-dependent volume translation predicted n-pentane density isotherms that cross one another at high pressures; hence, this model was not investigated further. More details will be presented for the experimental and modeling studies described here.